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Dr Behzad Fatahi

Biography

Dr. Fatahi has worked as a consulting and site geotechnical and railway engineer and has completed doctorate studies in Soft Soil Geomechanics from the University of Wollongong in Australia. Behzad is currently a full-time Assistant Professor/Lecturer of Geotechnical and Railway Engineering at the University of Technology Sydney, and Geotechnical Engineer at Coffey Geotechnics Pty Ltd, Sydney Office.

Behzad has immensely contributed to the idea of green corridors for railway lines. He has developed a novel model considering the coupled flow-deformation equations in soil to simulate influence of native vegetation of railway and road formation. He is a Chartered Professional Engineer. Since 2006, Dr. Fatahi has published over 20 peer reviewed Journal and Conference papers on the topic of green corridors for roads and railway lines. Dr. Fatahi was named 'Australasia Young Railway Engineer of Year 2007' by Engineers Australia and Railway Technical Society of Australasia. Behzad was also awarded the first prize at the Young Geotechnical Professional's Night in 2006, which is a prestigious geomechanics award from the Australian Geomechanics Society and Engineers Australia. He was also a first prize-winner at UOW's Higher Degree Research Conference in 2005 in the category "Frontier Technologies for Building and Transforming Australian Industries".

Dr. Fatahi is the reviewer of several international geotechnical journals. He has been involved in many ground improvement projects in Australia and overseas. His research and practical interests include Ground Improvement Techniques for Roads and Railway Lines, Viscous Behaviour of Clays, Bioengineering, Soil-Structure-Interaction, and Unsaturated Soil Mechanics.

Professional

  • Engineers Australia, MIEAust, CPEng
  • National Professional Engineers Register (NPER)
  • Australian Geomechanics Society (AGS)
  • Railway Technical Society of Australasia (RTSA)
  • International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE)
  • American Society of Civil Engineers (ASCE)
Image of Behzad Fatahi
Senior Lecturer, School of Civil and Environmental Engineering
Core Member, Centre for Built Infrastructure Research
Associate Member, Centre for Technology in Water and Wastewater
B.Sc (UT), M.Sc, PhD (UoW)
Member, National Professional Engineers Register
Chartered Engineer, Institution of Engineers, Australia
Chartered Engineer, National Professional Engineers Register
Member, Institution of Engineers, Australia
 
Phone
+61 2 9514 7883
Room
CB11.11.223

Research Interests

Geotechnical engineering; soft soil engineering, ground improvement techniques; bioengineering; embankment dam design and construction; numerical modelling in geomechanics; Soil-Structure Interaction; and secondary consolidation of clay

Can supervise: Yes
- PhD - MEng - BEng

48360, Geotechnical Engineering
48330, Soil Behaviour
49119, Problematic Soils and Ground Improvement Techniques
49254, Advanced Soil Mechanics and Foundation Design
49118, Applied Geomechanics,
48310, Introduction to Civil Engineering

Book Chapters

Indraratna, B., Fatahi, B. & Khabbaz, H. 2007, 'Finite Element Modelling of Soil-Vegetation Interaction' in T. Schanz (ed), Theoretical and Numerical Unsaturated Soil Mechanics, Springer, Germany, pp. 211-223.
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Behaviour of soils in the vadose zone is closely linked to water balance between ground and atmosphere. It seems that transpiration is the most uncertain and difficult to evaluate of all the terms in the soil water balance. The key variable to estimate the transpiration rate is the rate of root water uptake, which depends on the hydrological, geological and meteorological conditions. A mathematical model for the rate of root water uptake incorporating the root growth rate, ground conditions, type of vegetation and climatic parameters, has been developed. A conical shape is considered to represent the geometry of the tree root zone. Using this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. Field measurements taken from literature published previously are compared with the authors++ numerical model. The predicted results obtained from the numerical analysis, compared favourably with the field measurements, justifying the assumptions upon which the model was developed. The analysis also indicates that soil suction and settlement increase over the time, with the effect being more significant in the first stages of transpiration.

Conference Papers

Nguyen, L., Fatahi, B. & Khabbaz, H. 2014, 'Modelling Behaviour of Cemented Clay capturing cementation degradation', GeoShanghai International Conference 2014, Shanghai, China, May 2014 in GEOTECHNICAL SPECIAL PUBLICATION NO. 238, ed Jie Han, Anand Puppala,Shuilong Shen, Sadik Oztoprak, Jie Huang, American Society of Civil Engineers, United States of America., pp. 168-177.
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Le, T., Fatahi, B. & Khabbaz, H. 2014, 'Numerical solution to predict visco-plastic model parameters of soft clay during excess pore water pressure dissipation', Delft, the Netherlands, June 2014 in Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, ed Michael A. Hicks, Ronald B. J. Brinkgreve, Alexander Rohe, Taylor and Francis Group, London, UK, pp. 175-180.
Parsa Pajouh, A., Fatahi, B., Khabbaz, H. & Vincent, P. 2014, 'Evaluating Proposed Solutions for Equivalent Plane Strain Modeling of PVD Assisted Preloading', Sustainable Civil Infrastructures: Innovative Technologies and Materials: GeoHubei 2014, China, July 2014 in Advances in Transportation Geotechnics and Materials for Sustainable Infrastructure (GSP 250): GeoHubei 2014, ed Bulut, R. and Hsu, S.C., ASCE, USA, pp. 9-16.
In this study, a numerical code has been developed using FLAC 2D to model the prefabricated vertical drain (PVD) assisted preloading process considering the smear zone, and evaluate the efficiency of the proposed equations for the conversion of permeability coefficient from axisymmetric state to plane-strain condition. A laboratory PVD assisted preloading test has been conducted employing a fully instrumented large Rowe cell to verify the developed numerical code. The results of the numerical plane-strain and axisymmetric simulations have been compared using four methods of permeability conversion from axisymmetric to plane-strain condition.
Azari, B., Fatahi, B., Khabbaz, H. & Vincent, P. 2014, 'Elastic Visco-Plastic Behaviour of Soft Soils Improved with Preloading and Vertical Drains', Sustainable Civil Infrastructures: Innovative Technologies and Materials: GeoHubei 2014, China, July 2014 in Pavement Performance Monitoring, Modeling, and Management (GSP 254):GeoHubei 2014, ed Steyn, W. J., Chen, X., and Nam, B., ASCE, USA, pp. 17-24.
In this study, a numerical solution adopting an elastic visco-plastic model with nonlinear creep function incorporated in the consolidation equations has been developed to investigate the time dependant behaviour of soft soil deposits improved with vertical drains and preloading. The employed elastic visco-plastic model is based on the framework of the modified Cam-Clay model capturing soil creep during excess pore water pressure dissipation. Besides, nonlinear variations of creep strain rate with stress and time and permeability variations during the consolidation process are considered. The developed numerical model is validated against Ska-Edeby test fill with the available long-term settlement and excess pore water pressure monitoring results for the soft clay deposit improved with vertical drains assisted preloading. Practicing engineers can adopt the developed code and guidelines to predict the long term performance of embankments on soft soil improved using preloading.
Khabbaz, H., Lin, E.X. & Fatahi, B. 2014, 'A Parametric Study on Shoring Structures with Multi-row Anchors in Layered Soil', Sustainable Civil Infrastructures: Innovative Technologies and Materials: GeoHubei 2014, China, July 2014 in Earthwork Project Management, Slope Stability Analysis, and Wave-Based Testing Techniques (GSP 252): GeoHubei 2014, ed Chen, S.E., Chang, D.T., and Lee, Y., ASCE, USA, pp. 81-88.
This paper examines two numerical methods commonly used in shoring design, namely the beams on elastic foundation method using WALLAP and the finite element method (FEM) using PLAXIS. Numerous design parameters are also investigated to study the effects of the parametric variations on each method. The shoring model analysed in this study is based on a deep excavation project in Sydney central business district. One of the significant findings of this study is that the results obtained from both WALLAP and PLAXIS show marginal numerical errors, which in turn need to be examined closely. Generally, the beams on elastic foundation method is more conservative than the FEM. In comparison with the FEM, the soil modulus has more significant effects than the shear strength parameters in the beams on elastic foundation method. Moreover, the resulting shear forces, bending moments and lateral displacements of the shoring are less sensitive to the variation of the soil friction angle than the cohesion. The findings of this study can be taken into consideration by practicing civil engineers, when designing appropriate shoring systems in urban areas.
Fatahi, B., Sadeghi Hokmabadi, A. & Samali, B. 2014, 'Seismic Performance Based Design for Tall Buildings Considering Soil-Pile- Structure Interaction', GeoShanghai 2014 (Advances in Soil Dynamics and Foundation Engineering GSP 240), Shanghai, May 2014 in GeoShanghai 2014 (Advances in Soil Dynamics and Foundation Engineering GSP 240), ed Liang, R.Y., Qian, J., and Tao, J., ASCE, USA, pp. 333-342.
Soil-Structure Interaction (SSI) plays a significant role in seismic response of the structures by altering the dynamic properties of the system and increasing the lateral deflection which in turn could change the performance level of structures. In this study, in order to experimentally investigate the influence of different types of foundations on SSI phenomena, a series of shaking table tests has been conducted considering four different cases, namely: (i) fixed-base structure representing the situation excluding the soil-structure interaction; (ii) structure supported by shallow foundation on soft soil; and (iii) structure supported by floating pile foundation in soft soil, and (iv) structure supported by end-bearing pile foundation in soft soil. Benchmark earthquakes including the 1995 Kobe, the 1994 Northridge, the 1968 Hachinohe, and the 1940 El Centro earthquakes are adopted. Results indicate that presence and type of pile foundations change the dynamic characteristics and behaviour of the superstructure which should be considered in predicting the damage level of structural and non-structural elements.
Ho, L.H., Fatahi, B. & Khabbaz, H. 2014, 'One-Dimensional Consolidation of Unsaturated Soil Deposit with Various Initial Conditions', GeoShanghai 2014 (Soil Behavior and Geomechanics GSP 236), Shanghai, May 2014 in GeoShanghai 2014 (Soil Behavior and Geomechanics GSP 236), ed Zhang, S., Chu, J., and Bulbut, R., ASCE, USA, pp. 145-155.
This study presents a novel analytical solution for one-dimensional (1-D) consolidation for unsaturated soils using the Eigen function expansion method to solve inhomogeneous governing equations of air and water phases. Eigen functions and eigenvalues are parts of the general solution and can be obtained based on the proposed boundary condition. Additionally, the Laplace transform method is adopted to solve the first-order differential equations. Once equations with transformed domain are all obtained, the final solutions, which are proposed to be functions of time and depth, can be achieved by taking an inverse Laplace transform. The mathematical procedure accentuates a non-uniform initial condition, in which initial excess pore pressures are linearly decreasing with depth. Dimensionless parameters and that control the gradients of distributions of initial excess pore-air and pore-water pressures, respectively, are introduced in this paper. A worked example is provided to investigate effects of and on the consolidation behaviour of unsaturated soils.
Ho, L.H., Fatahi, B. & Khabbaz, H. 2014, 'Analytical solution for one-dimensional consolidation of unsaturated soil deposit subjected to step loading', Unsaturated Soils: Research & Applications (UNSAT2014), Sydney, July 2017 in Unsaturated Soils: Research & Applications (UNSAT2014), ed Khalili, N., Russell, A., and Khoshghalb, A., Taylor & Francis Group, London, pp. 1763-1769.
This paper discusses a simple yet precise analytical solution for one-dimensional (1-D) consolidation of an unsaturated soil deposit subjected to a step loading. This solution is derived from nonlinear governing equations of flow using eigenfunction expansions and Laplace transform techniques. In addition, the mathematical development adopts one-way drainage condition for the unsaturated soil, in which the top boundary is permeable to the air and water phases whereas the base is impervious to these phases. Eigenfunctions and eigenvalues are parts of the general solution and can be obtained based on the proposed drainage boundary condition. Furthermore, uniformly distributed initial pore pressures can be used to determine the initial generalised Fourier coefficients. The Laplace transform method is adopted to solve the first-order differential equations. Once the equations with transformed domain are obtained, the final solutions, which are proposed to be functions of time (t) and depth (z), can be achieved by taking an inverse Laplace transform. A worked example is provided to present the consolidation characteristics of unsaturated soils based on the proposed solution. Significance of air to water permeability ratio on the excess pore-water and pore-air pressure dissipation and compression is investigated and discussed.
Fatahi, B., Le, T. & Khabbaz, H. 2013, 'INFLUENCE OF SOIL CREEP ON STABILITY OF EMBANKMENT ON SOFT SOIL', International conference on Grownd Improvement and Ground Control: ICGI 2012, Wollongong, Australia, October 2012 in Ground Improvement and Ground Control, ed Indraratna, B., Rujikiatkamjorn, C., Vinod, J., Research Publishing, SINGAPORE, pp. 485-490.
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As a result of the scarcity of land for construction, number of projects to construct man-made islands or to expand lands over soft grounds keeps increasing. Consolidation and creep are significant in the soft soil and hence, their long term deformation must be taken into account in engineering design and practice. Soil creep has significant impacts on the stability of the structures constructed on the soft ground. In this paper, a case study of an embankment constructed in stages in north Boston over a thick layer of Boston Blue Clay is numerically investigated in order to consider the effects of the soil creep. The behaviour of the ground is simulated using a finite element program associated with and without soil creep. A parametric study on the soil creep ratio is conducted to evaluate its effects on the predictions of the excess pore water pressure and lateral displacement. It is observed that the increase in the value of creep index causes the increases in both of the horizontal displacements and excess pore water pressures of the ground. In addition, the factor of safety against slope instability decreases with the creep ratio. Thus, the effects of soil creep should be earnestly considered in predicting the ground performance under embankments.
Fatahi, B., Le, T. & Khabbaz, H. 2013, 'Influence Of Insitu Stresses On Deformation And Stability Of Embankments On Deep Clays', Ground Improvement And Ground Control: Transport Infrastructure Development and Natural Hazards Mitigation, Wollongong, Australia, October 2012 in Proceedings of the International Conference on Ground Improvement and Ground Control, ed Indraratna, B., Rujikiatkamjorn, C., Vinod, J., Research Publishing, Singapore, pp. 491-496.
Time dependent behavior of soft soils under embankments is one of the challenging problems in geotechnical engineering, since soft ground has been utilised for development. This paper presents a numerical study of the influence of the initial stress state on the ground lateral deformation and pore water pressure by revisiting a case study of an embankment constructed on Boston Blue Clay. The insitu stress state is usually determined by the coefficient of lateral earth pressure at rest (K0), but there are various correlations to estimate the value of K0. In this paper, a numerical parametric study is conducted to investigate the effect of K0 on the vertical and horizontal displacements, the excess pore water pressures, and the factor of safety of the embankment. The results show that the value of K0 has notable influences on the predictions of horizontal and vertical displacements, but minor effects on the predicted pore water pressures. The choice of the lateral earth pressure coefficient at rest also has impact on the long term stability of the embankment. Thus, it is emphasised that the initial stress state should be concerned regarding the stability of the embankment for analysing the performance of embankments constructed on deep soft soils.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2013, 'Inelastic lateral seismic response of building frames under influence of bedrock depth variations incorporating soil-structure interaction', 22nd AUSTRALIAN CONFERENCE ON THE MECHANICS OF STRUCTURES AND MATERIALS, Sydney, Australia, December 2012 in From materials to structures: Advancement through innovation, ed Samali, B., Attard, M.M., Song, C., CRC press/Balkema, Netherlands, pp. 587-592.
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In this study, a fifteen storey moment resisting building frame is selected in conjunction with a soft clayey soil, representing soil class Ee, according to Australian Standards. Different bedrock depths including 10 m, 20 m, and 30m are employed in the numerical modelling using finite difference software FLAC 2D. The above mentioned frame has been analysed under two different boundary conditions: (i) fixed-base (no soilstructure interaction), and (ii) flexible-base (considering soil-structure interaction). Inelastic dynamic analyses under influence of different earthquake records for three mentioned bedrock depths are conducted, and the results in terms of inelastic lateral deflections and inter-storey drifts for the above mentioned boundary conditions are compared and discussed. The results indicate that the bedrock depth variations play a significant role in inelastic lateral seismic response of the building frame under the influence of soil-structure interaction. As the bedrock depth increases, lateral deflections and inter-storey drifts of the structures increase. The mentioned effects can change the performance level of the structures from life safe to near collapse or total collapse.
Azari, B., Fatahi, B. & Khabbaz, H. 2013, 'Long-term Viscoplastic Behaviour of Embankments Built on Improved Soft Soil Using Vertical Drains', STABILITY AND PERFORMANCE OF SLOPES AND EMBANKMENTS III, San Diego, California, March 2013 in GEOCONGRESS 2013, ed Meehan, C.L., Pradel, D., Pando, M.A., Labuz, J.F, American Society of Civil Engineers, Reston, Virginia, pp. 2124-2132.
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In this paper, a nonlinear elastic visco-plastic model is incorporated in the general consolidation equation to investigate the time dependent performance of embankments constructed over deep soft soil deposits stabilised with prefabricated vertical drains (PVDs) and preloading. To model vertical and radial consolidation processes, a finite difference formulation is implemented for fully coupled axisymmetric consolidation. The developed numerical model is validated against V+sby test fill with the available long-term settlement monitoring results for the soft clay deposit improved with PVDs assisted preloading. Practicing engineers can adopt the developed code and guidelines to predict the long term performance of embankments on soft soil consolidated using preloading.
Le, T., le, p.v., Khabbaz, H. & Fatahi, B. 2013, 'Stability and Deformation of Sheet Pile Walls for Protecting Riverside Structures in the Mekong River Delta', STABILITY AND PERFORMANCE OF SLOPES AND EMBANKMENTS III, San Diego, California, March 2013 in GEOCONGRESS 2013, ed Meehan, C.L., Pradel, D., Pando, M.A., Labuz, J.F, American Society of Civil Engineers, Reston, Virginia, pp. 1349-1358.
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Regions of the Mekong River Delta consist of soft soil, which causes significant issues on the stability and deformation of the surrounding structures, especially the riverside structures. Sheet pile walls are considered as one of the effective methods used to support the riverside structures against soil sliding and flooding. This paper presents a precise study on the stability and deformation of sheet pile walls constructed along the riverside areas in the Mekong River Delta. An approach founded on the limit equilibrium method is proposed to solve the equilibrium equations of lateral forces and moments. The proposed approach allows the designed depth of embedment to be determined by the factor of safety. Additionally, it is a simple method to analyze the performance of sheet walls in multi-layered ground conditions. A program code is written to implement the proposed method. In this paper, in order to evaluate the stability and deformation of the walls, the prediction results obtained by the developed method are compared to the results by finite element analysis. Furthermore, the results show that the predicted maximum lateral movement of the wall is in reasonable agreement with the field measurement.
Nguyen, L., Fatahi, B. & Khabbaz, H. 2013, 'Predicting behaviour of cemented clay considering strength reduction due to high confining pressure', GeoMontreal 2013, Montreal, Canada, September 2013 in GeoMontreal 2013, ed Chapuis, R., Canadian Geotechnical Society, Montreal, Canada, pp. 1-6.
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A predictive constitutive model referred to as Cemented Cam Clay (CCC) model developed by the authors is presented in this paper to precisely predict the behaviour of cemented clay capturing the effect of cementation degradation during loading. When the confining pressure increases, the effect of cementation gradually diminishes due to the breakdown of cementation bonds as observed in laboratory experiments. The proposed model includes a non-associated plastic potential function and elasto-plastic stress-strain relationship inspired by the framework of the critical state concept. The main feature of the proposed model is the formulation of the failure envelope which describes the beneficial effect of cementation at low pressure range. As the confining pressure continues to increase, it gradually merges with the critical state line indicating a degradation of cement bonding. The proposed model is validated through comparison of the model predictions with the results of an array of triaxial tests conducted on Ariake cemented clay.
Nguyen, Q., Fatahi, B. & Khabbaz, H. 2013, 'Three dimensional numerical simulation to predict performance of laterally loaded piles on clay-sand layered slope', GeoMontreal2013, Montreal, Quebec, September 2013 in GeoMontreal2013, ed Technical Committees, GeoMontreal2013, Montreal, Canada, pp. 1-6.
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Predicting the deformation of the laterally loaded piles constructed on a slope is one of the challenging issues in foundation engineering. Numerical modelling is an efficient method to investigate the effects of the distance from the pile centreline to the slope crest on the performance of laterally loaded piles considering the shear plastic deformations of the ground. In this paper, finite element software, ABAQUS, has been employed to simulate the performance of some piles subjected to lateral loads in the sloping ground including sand and clay layers. Appropriate subroutines have been adopted to simulate the soil-pile interface, capable of incorporating the gapping and sliding in the soil-pile interfaces for both sand and clay layers. The numerical results are used to predict the lateral load-deformation of piles for various cases and validated through comparison with an array of full scale field measurements.
Ho, L.H., Fatahi, B. & Khabbaz, H. 2013, 'Exact Solution to Predict Excess Pore Pressures and Settlement of Unsaturated Soil Deposit due to Uniform Loading', Hilton Bonaventure Montreal Hotel, September 2013 in GEO Montreal 2013, ed Robert, C., Canadian Geotechnical Society, Montreal, Quecbec, pp. 1-6.
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This paper explains a simple yet precise analytical solution for the nonlinear governing equations for one-dimensional (1D) consolidation of an unsaturated soil deposit using eigenfunction expansions and Laplace transform techniques. The mathematical development adopts two-way drainage condition for the unsaturated soil, in which the permeable top and base boundaries allow free dissipation of pore-air and pore-water pressures under uniform loading. Eigenfunctions and eigenvalues are parts of the general solution and can be obtained based on the proposed drainage boundary condition. Furthermore, uniformly distributed initial pore pressures can be used to determine the initial generalised Fourier coefficients. Besides, Laplace transform method is adopted to solve the first-order differential equations. Once the equations with transformed domain are obtained, the final solutions, which are proposed to be functions of time (t) and depth (z), can be achieved by taking an inverse Laplace transform. A worked example is provided to present the consolidation characteristics of unsaturated soils based on the proposed solution. Significance of air permeability to water permeability ratio on the excess pore water and air pressure dissipation rates is investigated and discussed.
Khabbaz, H., Shrestha, B. & Fatahi, B. 2013, 'Parametric Study On Behavior Of Reinforced Soil Walls With Combined Horizontal And Vertical Geosynthetics', 2013 AGS Symposium, Sydney, Australia, October 2013 in Retaining Structures: Recent Advances and Past Experiences - PROCEEDINGS OF THE 2013 AGS SYMPOSIUM, ed H. Khabbaz and C. Rujikiatkamjorn, The Australian Geomechanics Society, Australia, pp. 173-181.
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The reinforced soil system employing geogrids, as a cost effective reinforcement technique, has come to play an important role in a variety of civil and geotechnical engineering applications. In regular reinforced soil wal1s, the reinforcements are usually laid horizontally in the soil. In this study, the behaviour of reinforced soil retaining walls with combined horizontal and vertical reinforcements are investigated experimentally as well as numerically. The results, indicating the effects of vertical reinforcement inclusion, are compared to conventional reinforcing types under static and dynamic loads. The performance of retaining walls employing vertical reinforcement in conjunction with horizontal reinforcement is convincing from the results of the shake table tests conducted by the authors. In this paper, PLAXIS, well-known geotechnical software, is used for conducting a series of pararoetric studies on behaviour of reinforced soil walls under construction and subject to earthquake loading, incorporating the vertical reinforcement. The vertical reinforcement layout and its strength are among the major variables of the investigation. The geometry of the model, soil properties and reinforcement characteristics have been kept identical in all different cases selected for parametric studies. The performance of the wall is presented for the facing deformation and crest surface settlement, lateral earth pressure, tensile force in the reinforcement layers and acceleration amplification. The vertical ctefOlIDation, horizontal deflection, reinforcement force and earth pressure develop drastically under earthquake loading compared to the end of construction. The results show that these variables are considerably reduced when incorporating the vertical reinforcement in the system. In addition, the findings suggest better performance and higher structural safety for reinforced soil walls, when employing this proposed orthogonally horizontal-vertical geosynthetics.
Sadeghi Hokmabadi, A., Fatahi, B. & Samali, B. 2013, 'Seismic Response of Superstructure on Soft Soil Considering Soil-Pile-Structure Interaction', Challenges and innovations in geotechnics, Paris, France, September 2013 in Challenges and innovations in geotechnics. Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, ed Pierre DELAGE, Jacques DESRUES, Roger FRANK, Alain PUECH, Franscois SCHLOSSER, Presses des Ponts, Paris, France, pp. 547-550.
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This paper presents results of shaking table tests and three dimensional numerical simulations to investigate the influence of Soil-Pile-Structure Interaction (SPSI) on the seismic response of mid-rise moment resiting buildings supported by end-bearing pile foundations. Three different cases have been considered, namely: (i) fixed-base structure representing the situation excluding the soil-structure interaction; (ii) structure supported by shallow foundation on soft soil; 8nd (iii) structure supported by end-bearing pile foundation in soft soil. Comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil-structure interaction induces significant increase in the lateral deflections and inter-storey drifts of the structures on both shallow and end-bearing pile foundations in comparison to the fixed base structures. This increase in the lateral deformations and in turn inter-storey drifts can change the performance level of the structure during earthquakes which may be safety threatening.
Parsa Pajouh, A., Fatahi, B. & Khabbaz, H. 2013, 'Numerical Analysis to Quantify the Influence of Smear Zone Characteristics on Preloading Design in Soft Clay', International Conference on Soil Mechanics and Geotechnical Engineering, Paris, France, September 2013 in Challenges and innovations in geotechnics. Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, ed Pierre DELAGE, Jacques DESRUES, Roger FRANK, Alain PUECH, Franscois SCHLOSSER, Presses des Ponts, Paris, France, pp. 2573-2576.
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In this paper, the effects of uncertainties of smear zone charateristics induced by installation of. fabricated vertical drains on the preloading design are numerically investigated, FLAC 2D finite difference software with additional developed subroutines has been employed to conduct the numerical simulations. The finite difference analyses have been verified using a case study. Furthermore, a comprehensive parametric study is conducted to investigate the influence of iimear zone permeability and extent on the model predictions. Results of this study indicate that the assumplive properties for smear zone characteristics may result in inaccurate predictions of ground deformations and pore water pressures. This may lead to early removal of the surcharge in the construction process causing excessive post construction settlement. It is recommended to practising engineers to use results of trial preloading to back calculate the required smear zone characleristics in the early stages of embankment construction to optimize the design.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2012, 'Effects of soil dynamic properties and bedrock depth on seismic response of building frames incorporation soil-structure interaction', the 5th Asia-Pacific Conference on Unsaturated Soils Theory and Practice, Thailand, November 2011 in Proceedings of the 5th Asia-Pacific Conference on Unsaturated Soils Theory and Practice, ed Jotisankasa, A; Sawangsuriya, A; Soralump, S; Mairaing, W, Kasetsart University, Thailand, pp. 597-603.
In this study, a ten storey moment resisting building frame, resting on a shallow foundation,is selected in conjunction with three soil types with the shear wave velocities less than 600m/s, representing classes Ce, De and Ee, according to AS 1170.4. Different bedrock depths including 10m, 20m, and 30 m are employed in the numerical modelling using finite difference software FLAC 2D. Fully nonlinear dynamic analysis under influence of different earthquake records is conducted, and the results of the three different cases are compared and discussed. The results indicate that the dynamic properties of the subsoil such as shear wave velocity as well as bedrock depth play significant roles in seismic response of the building frames under the influence of soil-structure interaction. As the shear wave velocity of the subsoil decreases and bedrock depth increases, lateral deflections and inter-storey drifts of the structures increase. The mentioned effects can change the performance level of the structures from life safe to near collapse or total collapse. Therefore, the conventional design procedure excluding SSI is no longer adequate to guarantee the structural safety for the building frames resting on soft soil deposits.
Rujikiatkamjorn, C., Indraratna, B. & Fatahi, B. 2012, 'Numerical prediction of unsaturated ground behavior influenced by vegetation and vacuum consolidation', The 5th Asia-Pacific Conference on Unsaturated Soils Theory and Practice, Thailand, November 2011 in Proceedings of the 5th Asia-Pacific Conference on Unsaturated Soils Theory and Practice, ed Jotisankasa, A; Sawangsuriya, A; Soralump, S; Mairaing, W, Kasetsart University, Thailand, pp. 851-856.
Bioengineering including native vegetation is an ancient method of improving the stability of slopes. In modern railway engineering, this technique is re-captured for increasing the soil stiffness and shear strength of subgrade beneath rail tracks. Currently this practice has become increasingly popular in Australia for stabilising railway corridors built over expansive clays and compressive soft soils. This paper looks at the stabilisation role by suction generated by both the natural vegetation and the artificial vacuum application using the numerical analysis. For demonstrating the role of native vegetation, a mathematical model for the rate of root water uptake was incorporated in the analysis. The soil moisture content distribution and the soil matric suction profile adjacent to the tree were numerically captured based on the general effective stress theory of unsaturated soil. For vacuum application, the equivalent plane strain theory was employed to simulate radial consolidation and artificially applied suction. The performance of both techniques on track constructed on soft formation was discussed and compared in terms of settlement and associated pore pressure.
Fatahi, B., Tabatabaiefar, S., Sadeghi Hokmabadi, A. & Samali, B. 2012, 'Significance of bedrock depth in dynamic soil-structure interaction analysis for moment resisting frames', SECOND INTERNATIONAL CONFERENCE ON PERFORMANCE-BASED DESIGN IN EARTHQUAKE GEOTECHNICAL ENGINEERING, Italy, May 2012 in SECOND INTERNATIONAL CONFERENCE ON PERFORMANCE-BASED DESIGN IN EARTHQUAKE GEOTECHNICAL ENGINEERING, ed MAUGERI, M; SOCCODATO, C, Associazione Geotecnica Italiana - Roma, Italy, pp. 1396-1406.
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In this study, a fifteen storey moment resisting building frame, resting on a shallow foundation, is selected in conjunction with two clayey soils with the shear wave velocities less than 600m/s, representing soil classes De and Ee, according to AS 1170.4. Different bedrock depths including 10m, 20m, and 30 m are employed in the numerical modelling using finite difference software FLAC 2D. Fully nonlinear dynamic analysis under the influence of different earthquake records is conducted, and the results of the three different cases are compared and discussed. The results indicate that the dynamic properties of the subsoil such as shear wave velocity as well as bedrock depth play significant roles in seismic response of the building frames under the influence of soil-structure interaction. As the bedrock depth increases, lateral deflections and inter-storey drifts of the structures increase. These effects can change the performance level of structures from life safe to near collapse or total collapse. Therefore, the conventional design procedure excluding SSI is not adequate enough to guarantee the structural safety for the building frames resting on soft soil deposits.
Fatahi, B., Khabbaz, H. & Fatahi, B. 2012, 'Application of Polypropylene and Carpet Fibres to Improve Mechanical Properties of Cement Treated Clay', PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM, Brussel, May 2012 in International Symposium on Ground Improvement IS-GI, ed Technical Committee, SIMSG, Brussel, pp. 303-308.
In this study, the influence of two types of fibre reinforcement, namely polypropylene and carpet waste fibres, on mechanical properties of cement treated kaolinite is investigated. The results of unconfined compressive strength testing of 63 cylindrical samples of cement treated kaolinite with varied cement and fibre contents are analysed to discern the relationships between these parameters and the key mechanical properties, including unconfined compressive strength and stiffness of treated soil. The fibre reinforcement increases the peak strength. The initial Young's modulus of the fibre reinforced cement treated kaolinite increases by adding polypropylene whereas slightly decreases when adding carpet fibres. The improvement of mechanical properties was far more pronounced with the introduction of polypropylene than carpet waste fibres. The implication of these findings is a cost effective and environmentally friendly alternative compare to increasing cement content in soil to achieve the required mechanical properties, particularly where the strength is a governing consideration.
Khabbaz, H., Fatahi, B. & Nucifora, C. 2012, 'Finite Element Methods against Limit Equilibrium Approaches for Slope Stability Analysis', 11th Australia - New Zealand Conference on Geomechanics - Ground Engineering in a Changing World, Melbourne, Australia, July 2012 in 11th Australia - New Zealand Conference on Geomechanics - Ground Engineering in a Changing World (ANZ 2012) Conference Proceedings, ed G Narsilio, A Arulrajah, and J Kodikara, Geomechanical Society and New Zealand Geotechnical Society, Melbourne, Australia, pp. 1293-1298.
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A number of powerful numerical models, including limit equilibrium and finite element (FE) methods, have been developed for slope stability analysis in recent decades. The limit equilibrium method contains several limitations, yet is considered the most common approach. However, the advancement of technology has increased the use of the finite element method as it embraces a wider range of features. The limit equilibrium software, SLOPE/W, and the FE program PLAXIS are two common software programs currently employed in geotechnical engineering. Slope analysis using the limit equilibrium method involves a series of slip surfaces dividing ground into vertical slices, and using the static equilibrium equations to calculate the factor of safety (FOS) and stresses for each slice. PLAXIS requires the input of soil properties and elastic-plastic parameters of elements. In this study the properties of a heterogeneous slope, consisting of general fill embankment over soft, slightly overconsolidated clay is implemented in each program. The FOS of slopes is determined for subsequent design requirements, and results are analysed and comparisons are conducted. The effect of Young++s modulus on the FOS is also discussed. Recommendations are provided based on the results and previously published findings. The contribution of this paper is beneficial to geotechnical engineers, as it discusses the suitability and limitations of each method and assesses reliability of model outputs for slope stability analyses.
Mirlatifi, S. & Fatahi, B. 2012, 'Numerical Analysis of Geosynthetic Reinforced Soil Wall as Bridge Abutment', 11th Australia - New Zealand Conference on Geomechanics - Ground Engineering in a Changing World, Melbourne, Australia, July 2012 in 11th Australia - New Zealand Conference on Geomechanics - Ground Engineering in a Changing World (ANZ 2012) Conference Proceedings, ed G Narsilio, A Arulrajah, and J Kodikara, Geomechanical Society and New Zealand Geotechnical Society, Melbourne, Australia, pp. 1383-1388.
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This paper presents the finite element analysis of a geosynthetic reinforced soil wall as a bridge abutment built in Tehran, and the predictions are compared with the available field measurements. This abutment is analysed using both Limit Equilibrium Method (LEM) for stability analysis and Finite Element Method (FEM) for deformation analysis. Two dimensional plane strain finite element model is adopted for the simulation. Polyvinyl Alcohol (PVA) geogrid with high tensile moduli and low creep characteristics has been adopted in this project to limit the deformation of the bridge abutment. In this model, the backfill soil and geogrids simulated adopting Mohr-Coulomb model, and the elasto-plastic material model that only works in tension, respectively. Bridge abutments can be stabilised by including geosynthetic layers with high tensile moduli satisfying both stability and deformation criteria reducing the construction cost and time, post construction deformations, and future maintenance cost.
Sadeghi Hokmabadi, A., Fatahi, B., Tabatabaiefar, S. & Samali, B. 2012, 'Effects of soil-pile-structure interaction on seismic response of moment resisting buildings on soft soil', 3rd International Conference on New Developments in Soil Mechanics and Geotechnical Engineering, Turkey, June 2012 in 3rd International Conference on New Developments in Soil Mechanics and Geotechnical Engineering, ed C. ATALAR, F. CiNiCiOGLU, B. M. DAS, A. SAGLAMER, E. TOGROL, Near East University Press, Turkey, Turkey, pp. 377-385.
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Dynamic response of structures sitting on soft soils is influenced by the soil properties, and the response is significantly different to the fixed base condition owing to the interaction between the ground and the structure, In order to study this effect, a fifteen storey moment resisting building frame, representing a conventional type of regular mid-rise building frame, resting ,on soil type Ee according to Australian Earthquake action code with the shear wave velocity equal to 150 mls is adopted. The numerical analysis using FLAC2D software is carried out for three different cases, namely: (1) fixed-base structure representing the situation excluding the soil-structure interaction (SSI); (2) structure supported by shallow foundation on soft soil; and (3) structure supported by pile foundation in soft soil. Benchmark earthquakes including the 1995 Kobe, the 1994 Northridge, the 1968 Hachinohe, and the 1940 EI Centro earthquakes are adopted. Results indicate that considering soil-structure interaction in both cases with shallow and pile fouudations is vital, and the conventional desigu procedure excluding soil-structure interaction is not adequate to guarantee the structural safety for the moment resisting buildings resting on the soft soil.
Fatahi, B., Khabbaz, H. & Le, T. 2012, 'Improvement of rail track subgrade using stone columns combined', Advances in Transportation Geotechnics II, Hokkaido, Japan, September 2012 in Proceedings of the 2nd Int'l Conference on Transportation Geotechnics (2nd ICTG) - Advances in Transportation Geotechnics II, ed Seiichi Miura, Tatsuya Ishikawa, Nobuyuki Yoshida, Yoshio Hisari and Nagato Abe, CRC Press - Taylor & Francis Group, London, UK, pp. 202-206.
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This study seeks to identify the effectiveness of ground improvement using stone columns in controlling settlement of soft soils when placed under the dead loads of the rail structure and the large live loads of freight trains. The employed numerical study assesses the relationship between the column position in the track cross section and the overall settlement of the ballasted rail formation. The numerical results show that the overall settlement of the track reduces significantly with the use of stone columns close to the centre of the track and not just under the rail. In addition, application of one layer of geogrids between sub-ballast and sub-grade assists to reduce the maximum settlement of track decreasing the future maintenance costs.
Fatahi, B., Engelbert, D., Mujic, S. & Khabbaz, H. 2012, 'Assessment of Surcharging on Strength and Stiffness of Cement Treated Clays', Grouting and Deep Mixing 2012, Louisiana, USA, February 2012 in Proceedings of the Fourth International Conference on Grouting and Deep Mixing 2012, ed Lawrence F. Johnsen, Donald A. Bruce, Michael J. Byle, AMERICAN SOCIETY OF CIVIL ENGINEERS (ASCE), USA, pp. 272-280.
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Deep soil mixing (DSM) is a ground improvement technique most appropriate in applications aimed at improving properties of soft clay, which is very sensitive to temperature and water content changes. This paper presents an experimental study capturing effects of surcharge application during curing time on the stress-strain behaviour of DSM columns. An investigation has been undertaken into the effects of varying surcharges, applied immediately after mixing, ranging from 40kPa to 120kPa, on the strength and stiffness of cement treated kaolinite clay samples with different cement contents. The results of uniaxial tests are analysed to illustrate how the Young++s modulus and unconfined compressive strength (UCS) are influenced under varying surcharges. Results confirm a promising increase in strength and stiffness with increased preloading. Results are significant, in that desired DSM column strengths can be achieved through a combination of cement and surcharging, as opposed to increasing the cement content; thus significantly reducing the carbon footprint induced by cement production.
Khabbaz, H. & Fatahi, B. 2012, 'GENERAL AND TECHNICAL CONSIDERATIONS FOR IMPLEMENTING HIGH SPEED RAIL SYSTEMS IN AUSTRALIA', ADVANCES IN GEOTECHNICAL ASPECTS OF ROADS AND RAILWAYS, Darling Harbour, NSW, Australia, October 2012 in PROCEEDINGS OF THE 2012 AGS SYMPOSIUM: ADVANCES IN GEOTECHNICAL ASPECTS OF ROADS AND RAILWAYS, ed H. Khabbaz, C. Y. Tey, O. Stahlhut and C. Rujikiatkamjorn, The Australian Geomechanics Society, Australia, pp. 67-78.
Australia has a number of medium speed rail services such as the Prospector, which runs from East Perth to Kalgoorlie, at speeds of up to 160 km/hr. Speeds as high as 210 km/hr have been reached by the tilt train from Brisbane to Rockhampton. Although there are a few medium speed rail systems in Australia, there is not a passenger rail transport with the high transit speeds seen in other countries. This paper presents the feasibility of implementing high speed rail systems in Australia by looking at the main elements that a high speed train is composed of. This paper also reviews the performance of high speed rail systems around the world and the factors contributed to their success made them successful. The main objective of this study is to look at how the solutions from overseas and how the technical requirements particularly the geotechnical aspects of tracks for a high speed rail system can be applied in Australian existing and new tracks. Australia has its own unique demographic, geographic and economic characteristics and the aim is to identify where there are overlaps between Australia++s characteristics and countries with high speed rail systems. High speed rail transport might not necessarily be one the best solutions for the transportation at present in Australia, but it can be what a nation needs to succeed in its future transportation system.
Samali, B., Fatahi, B. & Tabatabaiefar, S. 2011, 'Seismic behaviour of concrete moment resisting buildings on soft soil considering soil-structure interaction', Australasian Conference on the Mechanics of Structures and Materials, Melbourne, Australia, December 2010 in Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australasian Conference on the Mechanics of Structures and Materials (ACMSM21), ed Sam Fragomeni, Srikanth Venkatesan, Nelson T.K. Lam, Sujeeva Setunge, CRC Press/Balkema, The Netherlands, pp. 407-412.
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In this study, the effects of soil-structure interaction (SSI) on the seismic behaviour of reinforced concrete moment resisting building frames are studied using finite difference method. Two types of mid-rise structures, consisting of 5 and 15 stories on soft soil, are selected and analysed. The above mentioned frames are analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction), and (ii) considering soil-structure interaction. To model soil-structure interaction, the soil medium considering soil's non-linear damping and plasticity with interface elements between soil and structure is included. The results of the analyses in terms of structural forces and lateral displacements for the above mentioned boundary conditions for different earthquakes are compared. It is observed that lateral deflections and drifts ofthe structures increase when SSI is included.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2011, 'Effects of Dynamic Soil-Structure Interaction on Performance Level of Moment Resisting Buildings Resting on Different Types of Soil', Pacific Conference on Earthquake Engineering (PCEE) - 'Building an Earthquake Resilient Society', New Zealand, April 2011 in Proceedings of the 2011 Pacific Conference on Earthquake Engineering (PCEE), ed Technical Committee, New Zealand Society for Earthquake Engineering Inc., New Zealand, pp. 1-8.
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In this study, two structural models comprising five and fifteen storey moment resisting building frames are selected in conjunction with three different soil deposits with shear wave velocity less than 600m/s. The design sections are defined after applying dynamic nonlinear time history analysis based on inelastic design procedure using elastic-perfectly plastic behaviour of structural elements. These frames are modelled and analysed employing Finite Difference approach using FLAC 2D software under two different boundary conditions namely fixed-base (no soil-structure interaction), and considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results of inelastic behaviour of the structural models are compared. The results indicate that the inter-storey drifts of the structural models resting on soil types De and Ee (according to the Australian standard) substantially increase when soil-structure interaction is considered for the above mentioned soil types. Performance levels of the structures change from life safe to near collapse when dynamic soil-structure interaction is incorporated. Therefore, the conventional inelastic design procedure excluding SSI is no longer adequate to guarantee the structural safety for the building frames resting on soft soil deposits.
Fatahi, B. & Khabbaz, H. 2011, 'Enhancement of Ballasted Rail Track Performance Using Geosynthetics', Geohunan International Conference, Hunan, China, June 2011 in Advances in Pile Foundations, Geosynthetics, Geoinvestigations, and Foundation Failure Analysis and Repairs (GSP 220) Proceedings of the 2011 GeoHunan International Conference, ed Adam F. Sevi; Jiuyuan Liu; Cheng-wei Chen; Sao-Jeng Chao, ASCE, USA, pp. 222-230.
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The requirement of keeping a competitive edge against other means of transportation has increased the pressure on the railway industry to improve its efficiency and decrease the maintenance costs. In this paper, several solutions are presented to improve rail track foundations including optimum particle ballast grading and confining pressure as well as stabilising tracks overlying soft soils employing different techniques. This study specifically assesses the influence of shoulder ballast and its combination with geosynthetics to reduce the track settlement due to train load. Two dimensional plane strain finite element model is adopted to simulate the track deformation. Furthermore, the potential use of geosynthetics combined with recycled and blended ballast for reduction of rail displacement is addressed. The different location of geosynthetics in rail track substructure is examined. Rail track performance can be improved by including wider shoulder ballast with geosynthetic layer, and recycled and blended ballast reinforced with geosynthetics can be used during maintenance operation to curtail future track deformation.
Shrestha, B., Khabbaz, H. & Fatahi, B. 2011, 'Performance Analysis of Reinforced Soil Foundation Structures With Vertical Reinforcement', International Conference on Geotechnical Engineering for Disaster Mitigation and Rehabilitation, Indonesia, May 2011 in Proceedings of the 3rd International Conference on Geotechnical Engineering for Disaster Mitigation and Rehabilitation (3ICGEDMAR 2011), ed S. P. R. Wardani, J. Chu, S. C. Robert Lo, S. Iai, K. K. Phoon, World Scientific, Singapore, pp. 443-448.
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This study examines the performance of geosynthetic reinforced wall inserting vertical elements in conjunction with conventional horizontal reinforcements. In this system, similar to normal reinforcement, the selected granular material is compacted over the horizontal reinforcement up to the designed height and then another layer of horizontal reinforcement is laid down. Numerical investigations have been carried out using finite element software, PLAXIS. Geosynthetic reinforced soil foundation performance and its characteristics have been simulated with and without vertical reinforcement under static and dynamic loads. Numerical results show that the total settlement decreases by inserting inclined reinforcement in both static and dynamic loading in general, and particularly under seismic loading. A new bearing capacity formula incorporating the contribution of both vertical and horizontal reinforcements is also introduced based on the previously published studies and the outputs of this numerical simulation.
Fatahi, B., Tabatabaiefar, S. & Samali, B. 2011, 'Performance Based Assessment of Dynamic Soil-Structure Interaction Effects on Seismic Response of Building Frames', GEORISK 2011 - Geotechnical Risk Assessmenl & Management, Atlanta, Georgia, USA, June 2011 in PROCEEDINGS OF GEORISK 2011 - Geotechnical Risk Assessment & Management (Geotechnical Special Publication No. 224), ed C. Hsein Juang; Kok Kwang Phoon; Anand J. Puppala; Russell A. Green; Gordon A. Fenton, American Society of Civil Engineers (ASCE), USA, pp. 344-351.
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Soil-Structure Interaction (SSI) has progressed rapidly in the second half of 20th century stimulated mainly by requirements of the nuclear power and offshore industries to improve the seismic safety. In this study, a fifteen storey moment resisting building frame is selected in conjunction with three different soil deposits with shear wave velocity less than 600m/s. The design sections are defined after applying dynamic nonlinear time history analysis based on inelastic design procedure using elastic-perfectly plastic behaviour of structural elements. These frames are modelled and analysed employing Finite Difference approach using FLAC 2D software under two different boundary conditions, namely fixed-base (no soil-structure interaction), and considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results of inelastic behaviour of the structural model are compared. Variations of the shear modulus ratio with the shear strain are included in the nonlinear dynamic analysis. The results indicate that the inter-storey drifts of the structural model resting on soil types De and Ee (according to the Australian standard) substantially increase when soil-structure interaction is considered for the above mentioned soil types. Performance levels of the structures change from life safe to near collapse when dynamic soil-structure interaction is incorporated. Therefore, the conventional inelastic design procedure excluding SSI is no longer adequate to guarantee the structural safety for the building frames resting on soft soil deposits. Design engineers need to address the effects of dynamic SSI precisely in their design especially for construction projects on soft soils.
Azari, B., Fatahi, B. & Khabbaz, H. 2011, 'Application of Creep Ratio Concept for Estimating Post-Constriction Settlement of Deep Soft Clay Deposits', International Conference on Advances in Geotechnical Engineering, Perth, Australia, November 2011 in ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, ed Mohamed A. Shahin & Hamid R. Nikraz, Curtin University, Perth, Australia, pp. 127-133.
Two main different approaches have been previously proposed to predict time dependent behaviour of soft soils. (I) end of primary consolidation is unique although creep starts simultaneously with primary consolidation (Hypothesis A); (II) As creep and primary consolidation commence at the same time and creep is a time dependant phenomenon, then end of primary consolidation cannot be unique (Hypothesis B). In Hypothesis A, soil settlement is divided into two parts: primary consolidation and secondary compression which follows by primary consolidation. In Hypothesis B, soil settlement is estimated based on elasto-viscoplastic constitutive model simulating soil creep and consolidation settlement simultaneously. In this study, details of first approach based on creep ratio ( ) concept is discussed with a worked example to be used by practicing geotechnical engineers.
Le, T., Fatahi, B. & Khabbaz, H. 2011, 'Soil Creep Mechanisms and Inducing Factors', International Conference on Advances in Geotechnical Engineering, Perth, Australia, November 2011 in ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, ed Mohamed A. Shahin & Hamid R. Nikraz, Curtin University, Perth, Australia, pp. 241-246.
Soft soils have been utilised intensively for urbanisation and civil infrastructural development due to the scarcity of proper soils for construction. Soft soils themselves exhibit many engineering problems, such as large settlement which occurs in long time after construction. There are a large number of studies carried out to analyze that time dependent behaviour of soft soils, resulting in the variety of theories and models. The mechanism of creep deformation is the background to propose a model for predicting the long term settlement. However, there has been no unique explanation for the behavior of soils, leading to different theories of settlement analysis and prediction. There exist two main hypotheses for settlement calculation, Hypotheses A and B, distinguished based on different elucidation about creep mechanisms. From the existing research studies, this paper aims to discuss five mechanisms of creep including (i) the breakdown of interparticle bonds, (ii) the jumping of bonds of molecules, (iii) sliding movement among particles, (iv) the water drainage in double pore system, and (v) the structural viscosity. In this study, according to the explanation of creep mechanisms, the difference of the two hypotheses will be provided. This paper also suggests a creep mechanism based on the combinations of the explained mechanisms.
Parsa Pajouh, A., Fatahi, B. & Khabbaz, H. 2011, 'Numerical Back Analysis of Smear Zone Properties for Vertical Drain Assisted Preloading in Soft Soils', International Conference on Advances in Geotechnical Engineering, Perth, Australia, November 2011 in ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, ed Mohamed A. Shahin & Hamid R. Nikraz, Curtin University, Perth, Australia, pp. 561-566.
Installation of prefabricated vertical drains (PVDs) using a mandrel causes disturbance of the clay surrounding the drain, resulting in a smear zone of reduced permeability, which adversely affects consolidation process. There are two important parameters to characterize the smear effects, namely, the smear zone diameter and the permeability ratio. In this study, FLAC finites difference software has been employed to investigate the effects of smear zone characteristics on required time for preloading. The results of a fully instrumented trial embankment in Sunshine Motorway, Queensland, have been used to verify the model, and parametric studies have been conducted on the predicted ground settlement and pore water pressure. According to the results, changes in smear zone parameters can significantly affect the consolidation period. It is observed that the characteristics of smear zone namely size and permeability have a substantial impact on the preloading design to achieve a certain soil strength and stiffness satisfying both bearing capacity and settlement design criteria.
Shrestha, B., Khabbaz, H. & Fatahi, B. 2011, 'Experimental Evaluation of Seismic Deformation Characteristics of Vertical-Horizontal Reinforced Soil Walls', International Conference on Advances in Geotechnical Engineering, Perth, Australia, November 2011 in ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, ed Mohamed A. Shahin & Hamid R. Nikraz, Curtin University, Perth, Australia, pp. 797-802.
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Reinforced soils have been widely used in different construction applications including retaining walls. The performance of retaining walls employing vertical reinforcement in conjunction with horizontal reinforcement is investigated experimentally. This paper presents an experimental study of the seismic performance of vertical-horizontal reinforced soil wall on the simulated earthquake using reducedscale shake table tests. Construction of model retaining walls, instrumentation and results from shaking table tests are described in detail. Two types of reinforced walls, conventional horizontal reinforcement and vertical-horizontal reinforcement, were subjected to large shake of the earthquake motions. The geometry of the model, soil properties and reinforcement characteristics has been kept identical in all tests. The reinforcements used were polymeric geogrids, which were connected to the wrap-facing. Each consecutive horizontal reinforcement layers were connected in tension to each other with the help of vertical connections. The walls were instrumented using transducers to measure wall facing displacement, and accelerations within the soil. The magnitude of lateral displacement under base excitation significantly reduced when vertical reinforcement was included to the wall system.
Shrestha, B., Khabbaz, H. & Fatahi, B. 2011, 'Performance Comparison of Vertical-Horizontal with Conventional Reinforced Soil Walls Using Numerical Modelling', African Regional Conference on Soil Mechanics and G, University of Pretoria, Pretoria, South Africa, July 2011 in Proceedings of the 15th African Regional Conference on Soil Mechanics and Geotechnical Engineering, ed Carlos Quadros and S. W. Jacobsz, IOS Press, Netherlands, pp. 237-242.
Conventional reinforced soil walls have demonstrated acceptable performance during earthquake occurrences. Nevertheless, there is still some potential for enhancing the performance of these walls without increasing the cost significantly. This paper presents an overview on the application of vertical components to the reinforced soil in addition to the horizontal reinforcement. The performance of conventional and the modified reinforced soil walls are evaluated and compared to each other. In this study, a series of 2D models is carried out using PLAXTS, finite element software, to investigate behaviour of these walls. The performance of reinforced walls is evaluated under the seismic loads of Kobe earthquake. The results indicate that the proposed wall with vertical reinforcement has superior performance compared with the conventional method and can reduce the risk of failure during earthquakes.
Fatahi, B., Tabatabaiefar, S. & Samali, B. 2010, 'Influence Of Soil Characteristics On Seismic Response Of Mid-Rise Moment Resisting Buildings Considering Soil-Structure Interaction', Seismic Engineering Design for Management of Geohazards, Sydney, NSW, Australia, October 2010 in Seismic Engineering Design for Management of Geohazards - Proceedings of the 2010 Symposium, ed Cholachat Rujikiatkamjorn, Jessica McUveen, Roberta Lamont and Mike Haysler, The Australian Geomechanics Society, NSW, Australia, pp. 67-74.
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In this study, a fifteen storey moment resisting building frame, representing the conventional types of regular mid-rise building frames, resting on a shallow foundation, is selected in conjunction with three soil types with the shear wave velocity less that 600m/s, representing classes Ce, De and Ee, according to AS 1170.4. Characteristics of the employed soils have been extracted from the available geotechnical investigation reports of various projects. Furthermore, the structure is modelled considering the three mentioned types of the subsoil medium underneath employing the Finite Difference approach using FLAC 2D software. Three strong ground motion records adopted by the international community as benchmark earthquakes are used. These are the 1968 Hachinohe, the 1995 Kobe and the 1994 Northridge earthquakes. Fully nonlinear dynamic analysis under influence of different earthquake records is conducted, and the results of the three different cases are compared and discussed. The results indicate that the dynamic properties of the subsoil play a significant role in seismic response of the building frames under the influence of soil-structure interaction. As the shear wave velocity of the subsoil decreases, lateral deflections and inter-storey drifts of the structures increase which can change the performance level of the structures from life safe to near collapse or total collapse.
Tabatabaiefar, S., Samali, B. & Fatahi, B. 2010, 'Effects of Dynamic Soil-Structure Interaction on Inelastic Behaviour of Mid-Rise Moment Resisting Buildings on Soft Soils', Australian Earthquake Engineering Society Conference, Perth, Western Australia, November 2010 in AEES Conference 2010 - Australian Earthquake Engineering Society 2010 Conference, ed Kevin McCue, Sharon Anderson, Australian Earthquake Engineering Society, Perth, Australia, pp. 1-11.
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In this study, a ten storey moment resisting building frame, representing the conventional type of regular mid-rise building frames, resting on shallow foundation, is selected in conjunction with a clayey soil, representing subsoil class Ee, as classified in the AS 1170.4. The structural sections are designed after applying dynamic nonlinear time history analysis, based on both elastic method, and inelastic procedure using elastic-perfectly plastic behaviour of structural elements. The frame sections are modelled and analysed, employing Finite Difference Method using FLAC 2D software under two different boundary conditions: (i) fixed-base (no Soil-Structure Interaction), and (ii) considering Soil-Structure Interaction (SSI). Fully nonlinear dynamic analysis under influence of different earthquake records is conducted and the results of the two different cases for elastic and inelastic behaviour of the structural model are extracted and compared respectively. The results indicate that the lateral deflection increments for both cases are substantially dominating and can change the performance level of the structures from life safe to near collapse or total collapse. Therefore, conventional elastic and inelastic structural analysis methods assuming fixed-base structure may no longer be adequate to guarantee the structural safety. Therefore, considering SSI effects in seismic design of concrete moment resisting building frames resting on soft soil deposit is essential.
Parsa Pajouh, A., Fatahi, B. & Khabbaz, H. 2010, 'Uncertainties of Smear Zone Characteristics in the Design of Preloading with Prefabricated Vertical Drains', International Conference on Geotechnical Engineering and Soil Mechanics, Tehran, Iran, November 2010 in The 4th International Conference on Geotechnical Engineering and Soil Mechanics (ICSESM 2010), ed Technical Committee, Iranian Geotechnical Society (IGS), Iran, pp. 1-8.
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Installing prefabricated vertical drains using mandrels induces disturbance of the soil surrounding the drain, resulting in a smear zone with the reduced permeability. The required time for pore pressure dissipation in preloading design is strongly associated with the smear zone characteristics. In this study, the effects of smear zone properties on preloading time are numerically investigated. Parametric study is conducted to find out the range of smear zone parameters significantly influencing the consolidation period. It is observed that the characteristics of smear zone namely size and permeability have a substantial impact on the preloading design to achieve certain soil strength and stiffness satisfying both bearing capacity and settlement design criteria.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2010, 'Seismic Behaviour of Steel Moment Resisting Buildings on Soft Soil Considering Soil-Structure Interaction', European Conference on Earthquake Engineering, Ohrid, Macedonia, August 2010 in Proceeding of the 14 European Conference on Earthquake Engineering 2010, ed Technical Committee, Macedonian Association for Earthquake Engineering (MAEE), Macedonia, pp. 1720-1727.
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The 1985 Mexico City and many other recent earthquakes clearly illustrate the importance of local soil properties on the earthquake response of structures. These earthquakes demonstrated that the rock motions could be amplified at the base of the structure. Therefore, there is a strong engineering motivation for a site-dependent dynamic response analysis for many foundations to determine the free-field earthquake motions. The determination of a realistic site-dependent free-field surface motion at the base of the structure can be the most important step in the earthquake resistant design of structures. In this study, the effects of Soil-Structure Interaction on seismic behaviour of steel moment resisting building frames have been studied using Finite Difference Method. Two types of mid-rise structures, including 5 and 15 storey buildings on a soft soil deposit have been selected and analysed under influence of three different earthquake acceleration records. The above mentioned frames been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction), and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural forces and lateral displacements for the above mentioned boundary conditions have been compared and discussed. It is concluded that the dynamic soil-structure interaction plays a significant role in the seismic behaviour of the mentioned building frames including substantial increment in lateral inter-storey drifts of the structures and changing the performance level of the structures from life safe to near collapse or total collapse. Thus, Considering SSI effects in seismic design of steel moment resisting building frames resting on soft soil deposit is essential.
Fatahi, B., Khabbaz, H. & Indraratna, B. 2008, 'Analysis of Matric Suction Effects Induced by Tree Roots on Rail Track Subgrade', Conference on Railway Engineering, Perth, WA, Australia, September 2008 in Conference Proceedings: CORE2008 Conference on Railway Engineering, ed John Goodall, Bill Singleton, RTSA, Australia, pp. 599-610.
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This study investigates the eflects of vegetation on soil matric suction and ground deformation. This paper highlights the inter-related parameters contributing to the development of a conceptual evapo-transpiration and root water uptake equilibrium model that is then incorporated in a comprehensive numerical model. The developed numerical model based on the finite element analysis (ABAQUS) considers fully coupled flowdeformation behaviour of soil. The model formulation is based on the effective stress approach developed for unsaturated soils. Based on the proposed model, the distribution of the matric suction proflle adjacent to the tree has been numerically anaiysed. To validate the model, an array of field measurements conducted at Miram site in Victoria, Australia have been compared with the numerical predictions. Then behaviour of a single tree on improving soil behaviour underneath rail tracks has been described. II is found that root water uptake and associated matric suction stabilise the soft soil beneath railway lines and a pattern of trees grown systematically along rail corridors may olter a cost eltective and environmentally attractive solution for the soft ground improvement in the long-term.
Fatahi, B., Indraratna, B. & Khabbaz, H. 2008, 'Numerical and Experimental Study of Tree Influence on the Ground', Geo congress of the Geo-Institute of ASCE, New Orleans, USA, March 2008 in Proceedings of selected sessions of GeoCongress 2008: Characterisation, Monitoring, and Modelling of GeoSystems, ed Akram N. Alshawabkeh, Krishna R. Reddy, milind V. Khire, American Society of Civil Engineers (ASCE), USA, pp. 694-701.
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A mathematical model for the rate of root water uptake has been developed considering ground conditions, type of vegetation and climatic parameters. The three independent features in the root water uptake model incorporated in detail are soil suction, root distribution and potential transpiration A two dimensional finite element approach has been employed to solve the transient coupled flow and deformation equations in vicinity of a tree. To validale the model, an array off measurements and the data have been compared with the numerical predictions. The predicted results acquired from the numerical analysis have been compared favourably with the field and the associated laboratory measurements, justifying the assumptions, upon which the model has been developed.
Indraratna, B., Khabbaz, H. & Fatahi, B. 2008, 'Conceptual Development and Numerical Modelling of Vegetation Induced Suction and implications on Rail Track Stabilisation', International Conference of International Association for Computer Methods and Advances in Geomechanics, Goa, India, October 2008 in Proceedings of the 12th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG), ed Mahendra N. Jadhav, O. B. Bhendigeri, B. Hanumantha Rao, Anjan Patel, S. Shanthakumar, Suchit D. Gumaste, Sudarshan B.Shinde, Indian Institute of Technology, Bombay, Mumbai, India, pp. 4335-4344.
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The effects of tree roots on soil suction and ground settlement are investigated. This paper highlights the inter-related parameters contributing to the development of a conceptual evapo-transpiration and root water uptake equilibrium model that is then incorporated in a comprehensive numerical model. The developed numerical model based on the finite element analysis (ABAQUS) considers fully coupled flowdeformation behaviour of soil. Field measurements obtained by the authors from a field site in western Victoria and from past literature are used to validate the model. The predicted results show acceptable agreement with the field data in spite of the assumptions made for simplifying the effects of soil heterogeneity and anisotropy. The numerical analysis proves that the proposed root water uptake model can reliably predict the region of maximum matric suction away from the tree axis. The paper also compares the natural favourable effect of tree roots with the stabilising mechanisms of geosynthetic vertical drains subjected to vacuum pressure. Although this analogy is only justified for shallow vertical drains, the comparison still emphasises the obvious economical advantages of native vegetation.
Fatahi, B., Indraratna, B. & Khabbaz, H. 2007, 'Enhanced numerical analysis of ground behaviour influenced by tree root suction', Australia New Zealand Geomechanics conference, Brisbane, Australia, October 2007 in Common Ground: Proceedings of the 10th Australia and New Zealand Conference on Geomechanics, ed Jay Ameratunga, Brett Taylor, Matthew Patten, Coffey Geotechnics, Australia, pp. 142-147.
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Tree roots provide three stabilising functions: (a) reinforcement of the soil, (b) dissipation of excess pore pressures, (c) establishing sufficient matric suction to increase the shear strength. This paper looks at the way that vegetation influences soil moisture content distribution, and ground settlement. A theoretical model previously developed by the authors for the rate of tree root water uptake together with an associated numerical simulation is used in this study. Field measurements taken from literature published previously are compared with the authors' numerical model. The predicted results obtained from the numerical analysis, compared favourably with the field measurements, justifying the assumptions upon which the model was developed.
Fatahi, B., Indraratna, B. & Khabbaz, H. 2007, 'Analyzing Soft Ground Improvement Caused by Tree Root Suction', Geo-Denver 2007: New Peaks in Geotechnics, Denver, Colorado, USA, February 2007 in Advances in Measurement and Modeling of Soil Behavior : Proceedings of Sessions of Geo-Denver 2007, ed Don J. DeGroot, Cumaraswamy Vipulanandan, Jerry A. Yamamuro, Victor N. Kaliakin, Poul V. Lade, Mourad Zeghal, Usama El Shamy, Ning Lu, Chung R. Song, American Society of Civil Engineers (ASCE), USA, pp. 1-10.
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Bioengineering aspects of native vegetation are currently being evolved to improve soil stiffness, slope stabilisation, and erosion control. Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressures, and increasing the shear strength by induced matric suction. This paper looks at the way that vegetation influences soil matric suction, shrinkage, and ground settlement. A theoretical model previously developed by the authors for the rate of tree root water uptake together with an associated numerical simulation is used in this study. A conical shape is considered to represent the geometry of the tree root zone. Based on this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. Field measurements taken from previously published literature are compared with numerical predictions for further validation. The predicted results compared favourably with the measured results, justifying the assumptions upon which the model was developed. It is desirable to consider the influence zone of tree roots and the improved soil properties in modern geotechnical designs, benefiting from native vegetation.
Fatahi, B., Indraratna, B. & Khabbaz, H. 2006, 'Modelling of soil improvement induced by tree root suction', Sydney Chapter Symposium, Sydney, Australia, October 2006 in Soft Ground Engineering: Proceedings of the Sydney Chapter 2006 Symposium, ed Henk Buys, Paul Hewitt, Richard Moyle, Engineers Australia, ACT, Australia, pp. 155-166.
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Indraratna, B., Fatahi, B. & Khabbaz, H. 2006, 'Parametric Study on Suction Effects Induced by Tree Roots on Ground Conditions', Geo congress of the Geo-Institute of ASCE, Atlanta, Georgia, USA, February 2006 in GeoCongress 2006: Geotechnical Engineering in the Information Technology Age, Proceedings of GeoCongress 2006, ed Don J. DeGroot, Jason T. DeJong, J. David Frost, Laurie G. Baise, American Society of Civil Engineers (ASCE), USA, pp. 158-163.
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A model developed for the rate of tree root water uptake is applied numerically based on finite element analysis, to investigate the effects of the soil, tree and atmospheric parameters on the ground behaviour. The influences of potential transpiration rate, permeability coefficient, and the maximum root length density are studied and quantified. Although the rate of transpiration increases the soil matric suction and the ground settlement, permeability (saturated) decreases the matric suction generated and the corresponding settlement. The maximum root density also affects the change in peak matric suction as demonstrated in the paper.
Indraratna, B., Fatahi, B. & Khabbaz, H. 2006, 'Numerical Prediction of Vadose Zone Behaviour Influenced by Vegetation', International Conference on Unsaturated Soils, Arizona, USA, April 2006 in Proceedings of the 4th International Conference of Unsaturated Soils, ed Gerald A. Miller, Claudia E. Zapata, Sandra L. Houston, Delwyn G. Fredlund, American Society of Civil Engineers (ASCE), USA, pp. 2256-2267.
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Bioengineering aspects of native vegetation are currently, and rapidly, being evolved to improve soil stiffness, slope stabilisation, and erosion control. Apart from the reinforcement effect, tree roots establish sufficient matric suction to increase the shear strength and stiffness of the soil. This paper looks at the way, vegetation influences soil matric suction, shrinkage, and ground settlement. A mathematical model for the rate of root water uptake that considers ground conditions, type of vegetation and climatic parameters, has been developed. Based on this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. The model formulation is based on the general effective stress theory of unsaturated soils. Field measurements taken from literature published previously are compared with the authors' numerical model. The predicted results calculated using the soil, plant, and atmospheric parameters contained in the numerical model, compared favourably with the measured results, justifying the assumptions upon which the model was developed.
Fatahi, B. & Indraratna, B. 2006, 'Sensitivity analysis to examine tree root effectiveness in soft ground stabilisation', European Conference on Numerical Methods in Geotechnical Engineering, Austria, September 2006 in Proceedings of the 6th European Conference on Numerical Methods in Geotechnical Engineering, ed Helmut F. Schweiger, Balkema, Taylor & Francis Group, Netherlands, pp. 735-741.
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ABSTRACT: Native vegetation in Australia is becoming increasingly popular for stabilising railway corridors built over soft soils. A model previously developed to measure the rate of tree root water uptake and a computer model are used to investigate the effect of a wide range of soil, tree, and atmospheric parameters on partially saturated ground. First, sensitivity analysis is used to investigate the affect of different parameters on the maximum initial rate of root water uptake, and then a reference example is simulated using finite element analysis. The influence of parameters such as time, potential transpiration rate and its distribution factor, wilting point suction, the coefficient of permeability, and the distribution of root length density are studied. Soil suction and settlement was found to increase over time, with the effect being more significant in the first stages of transpiration. The most sensitive parameters are wilting point suction, the coefficient of saturation permeability at higher values, the rate of potential transpiration at lower values, and vertical root distribution when the coefficient is high.

Journal Articles

Sadeghi Hokmabadi, A., Fatahi, B. & Samali, B. 2014, 'Assessment of soil-pile-structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations', Computers and Geotechnics, vol. 55, no. 1, pp. 172-186.
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The role of the seismic soil+pile+structure interaction (SSPSI) is usually considered beneficial to the structural system under seismic loading since it lengthens the lateral fundamental period and leads to higher damping of the system in comparison with the fixed-base assumption. Lessons learned from recent earthquakes show that fixed-base assumption could be misleading, and neglecting the influence of SSPSI could lead to unsafe design particularly for structures founded on soft soils. In this study, in order to better understand the SSPSI phenomena, a series of shaking table tests have been conducted for three different cases, namely: (i) fixed-base structure representing the situation excluding the soil+structure interaction; (ii) structure supported by shallow foundation on soft soil; and (iii) structure supported by floating (frictional) pile foundation in soft soil. A laminar soil container has been designed and constructed to simulate the free field soil response by minimising boundary effects during shaking table tests. In addition, a fully nonlinear three dimensional numerical model employing FLAC3D has been adopted to perform time-history analysis on the mentioned three cases. The numerical model adopts hysteretic damping algorithm representing the variation of the shear modulus and damping ratio of the soil with the cyclic shear strain capturing the energy absorbing characteristics of the soil. Results are presented in terms of the structural response parameters most significant for the damage such as foundation rocking, base shear, floor deformation, and inter-storey drifts. Comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil+structure interaction amplifies the lateral deflections and inter-storey drifts of the structures supported by floating pile foundations in comparison to the fixed base structures. However, the floating pile foundations contribute to the reduction in the lateral displacements in comparison to the shallow foundation case, due to the reduced rocking components.
Khabbaz, H. & Fatahi, B. 2014, 'How to Overcome Geotechnical Challenges in Implementing High Speed Rail Systems in Australia', Geotechnical Engineering Journal of the SEAGS & AGSSEA, vol. 45, no. 1, pp. 39-47.
Although there are a few medium speed rail systems in Australia, there is not a passenger rail transport with the high transit speed, seen in other countries. This paper firstly summarises lessons learnt from other countries, experienced high speed rail (HRS) for many years. Then, the challenges associated with implementing HSR systems in Australia are explained. The main challenges include selection and design of proper tracks, geographical issues, environmental concerns, economics and project costs and construction procedures. The second part of the paper presents the effective solutions to the geotechnical challenges associated with HSR systems. Various approaches are presented to improve the ballast layer properties and enhance the track formation bearing strength, stiffness, resiliency and dynamic properties. Employing concrete slab (ballast-less) tracks is also taken into consideration for HSR systems, and their performance is compared to ballasted tracks.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2014, 'Numerical and Experimental Investigations on Seismic Response of Building Frames under Influence of Soil-Structure Interaction', Advances in Structural Engineering, An International Journal, vol. 17, no. 1, pp. 109-130.
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In this study, an enhanced numerical soil-structure model has been developed which treats the behaviour of soil and structure with equal rigour. The proposed numerical soil-structure model has been verified and validated by performing experimental shaking table tests. To achieve this goal, a series of experimental shaking table tests were performed on the physical fixed based (structure directly fixed on top of the shaking table) and flexible base (considering soil and structure) models under the influence of four scaled earthquake acceleration records and the results were measured. Comparing the experimental results with the numerical analysis predictions, it is noted that the numerical predictions and laboratory measurements are in a good agreement. Thus, the proposed numerical soil-structure model is a valid and qualified method of simulation with sufficient accuracy which can be employed for further numerical soil-structure interaction investigation studies. Based on the predicted and observed values of lateral deflections of fixed base and flexible base models, lateral deflections of the flexible base model have noticeably amplified in comparison to the fixed base model. As a result of the lateral deflection amplifications, it is observed that the performance level of the scaled structural model changed significantly which could be safety threatening.
Nguyen, L., Fatahi, B. & Khabbaz, H. 2014, 'A constitutive model for cemented clays capturing cementation degradation', International Journal of Plasticity, vol. 56, pp. 1-18.
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Laboratory experiments show that the effect of cementation on clays gradually diminishes as the confining pressure increases (particularly at high confining pressures) due to the degradation of cementation bonds. The main aim of this paper is to propose a constitutive model for cemented clays, referred to as the Cemented Cam Clay model (CCC), to simulate the cementation degradation during loading. The failure envelope of the proposed model is formulated to describe the behaviour of the cemented clay at a low pressure range similar to over-consolidated soils, while it merges with the Critical State Line of reconstituted sample gradually as the confining pressure continues to increase. In order to examine the stress+strain behaviour of cemented clays, an energy dissipation equation is developed inspired by the Modified Cam Clay model. The characteristics of the proposed model, including a non-associated plastic potential function and elasto-plastic stress+strain relationship, are presented in light of the Critical State concept. Validity of the proposed constitutive model derived from the modified energy equation is evaluated against triaxial test results for cemented clays available in literature.
Fatahi, B., Tabatabaiefar, S. & Samali, B. 2014, 'Soil-structure interaction vs Site effect for seismic design of tall buildings on soft soil', Geomechanics and Engineering: An International Journal, vol. 6, no. 3, pp. 293-320.
In this study, in order to evaluate adequacy of considering local site effect, excluding soil-structure interaction (SSI) effects in inelastic dynamic analysis and design of mid-rise moment resisting building frames, three structural models including 5, 10, and 15 storey buildings are simulated in conjunction with two soil types with the shear wave velocities less than 600 m/s, representing soil classes De and Ee according to the classification of AS1170.4-2007 (Earthquake actions in Australia) having 30 m bedrock depth. Structural sections of the selected frames were designed according to AS3600:2009 (Australian Standard for Concrete Structures) after undertaking inelastic dynamic analysis under the influence of four different earthquake ground motions. Then the above mentioned frames were analysed under three different boundary conditions: (i) fixed base under direct influence of earthquake records; (ii) fixed base considering local site effect modifying the earthquake record only; and (iii) flexible-base (considering full soil-structure interaction). The results of the analyses in terms of base shears and structural drifts for the above mentioned boundary conditions are compared and discussed. It is concluded that the conventional inelastic design procedure by only including the local site effect excluding SSI cannot adequately guarantee the structural safety for mid-rise moment resisting buildings higher than 5 storeys resting on soft soil deposits.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2014, 'An empirical relationship to determine lateral seismic response of mid-rise building frames under influence of soil-structure interaction', The Structural Design of Tall and Special Buildings, vol. 23, no. 7, pp. 526-548.
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n this study, to determine the elastic and inelastic structural responses of mid-rise building frames under the influence of soil+structure interaction, three types of mid-rise moment-resisting building frames, including 5-storey, 10-storey and 15-storey buildings are selected. In addition, three soil types with the shear wave velocities less than 600m/s, representing soil classes Ce, De and Ee according to AS 1170.4+2007 (Earthquake action in Australia, Australian Standards), having three bedrock depths of 10m, 20m and 30m are adopted. The structural sections are designed after conducting nonlinear time history analysis, on the basis of both elastic method and inelastic procedure considering elastic-perfectly plastic behaviour ofstructural elements. The frame sections are modelled and analysed, employing finite difference method adopting FLAC2D software under two different boundary conditions: (a) fixed base (no soil+structure interaction) and (b) considering soil+structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted, and the results in terms of the maximum lateral displacements and base shears for the above mentioned boundary conditions for both elastic and inelastic behaviours of the structural models are obtained, compared and discussed. With the results, a comprehensive empirical relationship is proposed to determine the lateral displacements of the mid-rise moment-resisting building frames under earthquake and the influence of soil+structure interaction.
Sadeghi Hokmabadi, A., Fatahi, B. & Samali, B. 2014, 'Seismic response of mid-rise buildings on shallow and end-bearing pile foundations in soft soil', Soils and Foundations, vol. 54, no. 3, pp. 345-363.
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The seismic behaviour of structures built on soft soil is influenced by the soil properties, and the response is significantly different from the fixed-base condition owing to the interaction between the ground and the structure. In this study, in order to investigate the influence of the foundation type on the response of structures, considering soil+structure interaction, a series of experimental shaking table tests has been conducted for three different cases, namely, (i) a fixed-base structure representing the situation excluding the soil+structure interaction; (ii) a structure supported by a shallow foundation on soft soil; and (iii) a structure supported by an end-bearing pile foundation in soft soil. A laminar soil container has been designed and constructed to simulate the free-field soil response by minimising the boundary effects. Simulating the superstructure as a multi-storey frame during the shaking table tests makes the experimental data unique. A fully nonlinear three-dimensional numerical model employing FLAC3D has been adopted to perform a time history analysis and to simulate the performance of the structure considering the seismic soil+structure interaction. Hysteretic damping of the soil is implemented to represent the variation in the shear modulus reduction factor and the damping ratio of the soil with cyclic shear strain. Free-field boundary conditions have been assigned to the numerical model and appropriate interface elements, capable of modelling sliding and separation between the pile and the soil elements, is considered. A comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil+structure interaction amplifies the lateral deflections and inter-storey drifts of structures supported by end-bearing pile foundations in comparison to fixed-base structures. However, pile foundations contribute more to the reduction in lateral displacements than shallow foundations due to the reduced rocking components. Consequently, the choice of foundation type is dominant and should be included when investigating the influence of SSI on the response of superstructures during shaking excitations, which is significantly important in the performance-based design of structures.
Ho, L.H., Fatahi, B. & Khabbaz, H. 2014, 'Analytical solution for one-dimensional consolidation of unsaturated soils using eigenfunction expansion method', International Journal for Numerical and Analytical Methods in Geomechanics, vol. 38, no. 10, pp. 1058-1077.
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This paper introduces an exact analytical solution for governing flow equations for one-dimensional consolidation in unsaturated soil stratum using the techniques of eigenfunction expansion and Laplace transformation. The homogeneous boundary conditions adopted in this study are as follows: (i) a one-way drainage system of homogenous soils, in which the top surface is considered as permeable to air and water, whereas the base is an impervious bedrock; and (ii) a two-way drainage system where both soil ends allow free dissipation of pore-air and pore-water pressures. In addition, the analytical development adopts initial conditions capturing both uniform and linear distributions of the initial excess pore pressures within the soil stratum. Eigenfunctions and eigenvalues are parts of the general solution and can be obtained based on the proposed boundary conditions. Besides, the Laplace transform method is adopted to solve the first-order differential equations. Once equations with transformed domain are all obtained, the final solutions, which are proposed to be functions of time and depth, can be achieved by taking an inverse Laplace transform. To verify the proposed solution, two worked examples are provided to present the consolidation characteristics of unsaturated soils based on the proposed method. The validation of the recent results against other existing analytical solutions is graphically demonstrated.
Fatahi, B., Khabbaz, H. & Indraratna, B. 2014, 'Modelling of unsaturated ground behaviour influenced by vegetation transpiration', Geomechanics and Geoengineering: An International Journal, vol. 9, no. 3, pp. 187-207.
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Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressure and increasing the shear strength by induced matric suction. This paper describes the way vegetation influences soil matric suction, shrinkage and ground settlement in the vadose zone through transpiration. A mathematical model for the rate of root water uptake, including the root growth rate considering ground conditions, type of vegetation and climatic parameters, has been developed. A finite element approach is employed to solve the transient coupled flow-deformation equations. The finite element mesh is built using partially saturated soil elements capable of representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the ground matric suction profile adjacent to the tree is numerically analysed. Current field measurements of soil matric suction and moisture content collected from Miram site located in Victoria State, Australia by the authors are compared with the numerical predictions. The results indicate that the proposed root water uptake model incorporated in the numerical analysis can be used for prediction of ground properties influenced by tree roots.
Fatahi, B. & Tabatabaiefar, S. 2014, 'Fully Nonlinear versus Equivalent Linear Computation Method for Seismic Analysis of Midrise Buildings on Soft Soils', International Journal of Geomechanics, vol. 14, no. 4, pp. 1-15.
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In this study, the accuracy of a fully nonlinear method against an equivalent linear method for dynamic analysis of soil-structure interaction is investigated comparing the predicted results of both numerical procedures. Three structural models, including 5-story, 10-story, and 15-story buildings, are simulated in conjunction with two soil types with shear-wave velocities less than 600?m/s. The aforementioned frames were analyzed under three different conditions: (1) fixed-base model performing conventional time history dynamic analysis under the influence of earthquake records, (2) flexible-base model (considering full soil-structure interaction) conducting equivalent linear dynamic analysis of soil-structure interaction under seismic loads, and (3) flexible-base model performing fully nonlinear dynamic analysis of soil-structure interaction under the influence of earthquake records. The results of these three cases in terms of average lateral story deflections and interstory drifts are determined, compared, and discussed. It is concluded that the equivalent linear method of the dynamic analysis underestimates the inelastic seismic response of midrise moment resisting building frames resting on soft soils in comparison with the fully nonlinear dynamic analysis method. Therefore, a design procedure using the equivalent linear method cannot adequately guarantee the structural safety for midrise building frames resting on soft soils.
Parsa Pajouh, A., Fatahi, B., Vincent, P. & Khabbaz, H. 2014, 'Analyzing consolidation data to predict smear zone characteristics induced by vertical drain installation for soft soil improvement', Geomechanics and Engineering: An International Journal, vol. 7, no. 1, pp. 105-131.
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In this paper, the effects of variability of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are investigated employing analytical and numerical approaches. Conventional radial consolidation theory has been adopted to conduct analytical parametric studies considering variations of smear zone permeability and extent. FLAC 2D finite difference software has been employed to conduct the numerical simulations. The finite difference analyses have been verified using three case studies including two embankments and a large-scale laboratory consolidometer with a central geosynthetic vertical drain. A comprehensive numerical parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Furthermore, the construction of the trial embankment is recommended as a reliable solution to estimate accurate smear zone properties and minimise the post construction settlement. A back-calculation procedure is employed to determine the minimum required waiting time after construction of the trial embankment to predict the smear zone characteristics precisely. Results of this study indicate that the accurate smear zone permeability and extent can be back-calculated when 30% degree of consolidation is obtained after construction of the trial embankment.
Tabatabaiefar, S. & Fatahi, B. 2014, 'Idealisation of soil-structure system to determine inelastic seismic response of mid-rise building frames', Soil Dynamics and Earthquake Engineering, vol. 66, no. 1, pp. 339-351.
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In this study, a novel and enhanced soil+structure model is developed adopting the direct analysis method using FLAC 2D software to simulate the complex dynamic soil-structure interaction and treat the behaviour of both soil and structure with equal rigour simultaneously. To have a better judgment on the inelastic structural response, three types of mid-rise moment resisting building frames, including 5, 10, and 15 storey buildings are selected in conjunction with three soil types with the shear wave velocities less than 600 m/s, representing soil classes Ce, De and Ee, according to Australian Standards. The above mentioned frames have been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction) and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural displacements and drifts for the above mentioned boundary conditions have been compared and discussed. It is concluded that considering dynamic soil-structure interaction effects in seismic design of moment resisting building frames resting on soil classes De and Ee is essential.
Fatahi, B. & Tabatabaiefar, S. 2014, 'Effects of Soil Plasticity on Seismic Performance of Mid-Rise Building Frames Resting on Soft Soils', Advances in Structural Engineering, An International Journal, vol. 17, no. 10, pp. 1387-1402.
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In this study, the effects of Plasticity Index (PI) variation on the seismic response of mid-rise building frames resting on soft soil deposits are investigated. To achieve this goal, three structural models including 5, 10, and 15 storey buildings are simulated in conjunction with a clayey soil representing soil class Ee according to the classification of AS1170.4-2007 (Earthquake actions in Australia) and then varying the Plasticity Index. Structural sections of the selected frames were designed according to AS3600-2009 (Australian Standard for Concrete Structures) after undertaking dynamic analysis under the influence of four different earthquake ground motions. The frame sections are modelled and analysed, employing finite difference method adopting FLAC 2D software under two different boundary conditions: (i) fixed base (no Soil-Structure Interaction), and (ii) flexible base considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results in terms of maximum lateral displacements and inter-storey drifts for the above mentioned boundary conditions are obtained, compared, and discussed. Base on the results of the numerical investigations, it becomes apparent that as the Plasticity Index of the subsoil increases, the base shears of mid-rise building frames resting on soft soil deposits increase, while the lateral deflections and corresponding inter-storey drifts decrease. It is concluded that reduction of the Plasticity Index could noticeably amplify the effects of soil-structure interaction on the seismic response of mid-rise building frames.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2013, 'Lateral seismic response of building frames considering dynamic soil-structure interaction effects', Structural Engineering and Mechanics, vol. 45, no. 3, pp. 311-321.
In this study, to have a better judgment on the structural performance, the effects of dynamic Soil-Structure Interaction (SSI) on seismic behaviour and lateral structural response of mid-rise moment resisting building frames are studied using Finite Difference Method. Three types of mid-rise structures, including 5, 10, and 15 storey buildings are selected in conjunction with three soil types with the shear wave velocities less than 600m/s, representing soil classes Ce, De and Ee, according to Australian Standard AS 1170.4. The above mentioned frames have been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction), and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural lateral displacements and drifts for the above mentioned boundary conditions have been compared and discussed. It is concluded that the dynamic soil-structure interaction plays a considerable role in seismic behaviour of mid-rise building frames including substantial increase in the lateral deflections and inter-storey drifts and changing the performance level of the structures from life safe to near collapse or total collapse. Thus, considering soil-structure interaction effects in the seismic design of mid-rise moment resisting building frames, particularly when resting on soft soil deposit, is essential.
Fatahi, B., Le, T., Le, M. & Khabbaz, H. 2013, 'Soil creep effects on ground lateral deformation and pore water pressure under embankments', Geomechanics and Geoengineering: An International Journal, vol. 8, no. 2, pp. 107-124.
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Analysing the behaviour of the soft ground under embankments is a challenging task and is of significant interest to practising geotechnical engineers. This paper revisits a well known case study of an embankment of Boston Blue Clay, which was thoroughly instrumented and measured with piezometers, settlement rods and inclinometers over a long time period during and after construction. The soil parameters were very comprehensively collected by both in situ and laboratory tests in several major test programs. The behaviour of the ground considering the modified Cam-Clay model including and excluding soil creep is simulated using finite element method. The analysed data are verified with field measurements and a parametric study is conducted to evaluate the influence of creep index on excess pore water pressures generated and the displacement of the ground under the embankment. It is observed that both horizontal displacements and excess pore water pressures of the ground under the embankment increased by the creep index. Thus effects of soil creep should be precisely considered in predicting the ground performance under embankments.
Fatahi, B., Fatahi, B., Le, T. & Khabbaz, H. 2013, 'Small-strain properties of soft clay treated with fibre and cement', Geosynthetics International, vol. 20, no. 4, pp. 286-300.
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To improve the dynamic properties of soft soil, the cement treatment technique combined with fibre reinforcement can be employed. In this study, the effects of two types of fibres (polypropylene and recycled carpet) on the hardening process and small-strain properties of cement-treated kaolinite and bentonite clays are investigated. Cement-treated clay specimens were prepared using cement contents of 5%, 10% and 15% by weight of dry soil for the kaolinite samples, and 30%, 40% and 50% for the bentonite samples. To investigate and understand the influence of different fibre types and contents, three different percentages of fibre content were adopted: 0.1%, 0.2% and 0.5% polypropylene fibres, and 0.5%, 0.75% and 1% carpet fibres. The results of bender element tests on 126 cylindrical samples of cement-treated clay with various cement and fibre contents were analysed to discern the relationships between fibre and cement content and the small-strain mechanical properties, including the shear wave velocity and maximum small-strain shear modulus of the treated soil. The influence of fibres and cement contents on the hardening time of treated soil has also been investigated.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2013, 'Seismic Behavior of Building Frames Considering Dynamic Soil-Structure Interaction', International Journal of Geomechanics, vol. 13, no. 4, pp. 409-420.
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The seismic excitation experienced by structures is a function of the earthquake source, travel path effects, local site effects, and soilstructure interaction (SSI) influences. The result of the first three of these factors is referred to as free-field ground motion. The structural response to free-field motion is influenced by the SSI. In particular, accelerations within structures are affected by the flexibility of the foundation support and variations between the foundation and free-field motions. Consequently, an accurate assessment of inertial forces and displacements in structures can require a rational treatment of SSI effects. In the current study, to depict these effects on the seismic response of moment-resisting building frames, a 10-story moment-resisting building frame resting on a shallow foundation was selected in conjunction with three soil types with shear-wave velocities of less than 600 m/s, representing Soil Classes Ce, De, and Ee according to an existing Australian Standard. The structural sections were designed after applying dynamic nonlinear time-history analysis, based on both the elastic method, and inelastic procedure using the elastic-perfectly plastic behavior of the structural elements. The frame sections were modeled and analyzed using the finite-difference method andthe FLAC 2D software under two different boundary conditions: (1) fixed-base (no SSI) and (2) considering the SSI. Fully nonlinear dynamic analysis under the influence of various earthquake records was conducted and the results of the two different cases for elastic and inelastic behavior of the structuralmodel were extracted, compared, and discussed. The results indicate that the performance level of themodel resting on Soil Class Ce does not change substantially and remains in the life safe level while the performance level of themodel resting on Soil Classes De and Ee substantially increase from the life safe level to near collapse for both elastic and inelastic cases. Thus, considering SSI effects in the elastic and inelastic seismic design of concrete moment-resisting building frames resting on Soil Classes De and Ee is essential. Generally, by decreasing the dynamic properties of the subsoil such as the shear-wave velocity and shear modulus, the base shear ratios decrease while interstory drifts of the moment-resisting building frames increase relatively. In brief, the conventional elastic and inelastic design procedure excluding the SSI is not adequate to guarantee structural safety for moment-resisting building frames resting on Soil Classes De and Ee.
Fatahi, B., Le, T., Fatahi, B. & Khabbaz, H. 2013, 'Shrinkage Properties of Soft Clay Treated with Cement and Geofibers', Geotechnical and Geological Engineering: an international journal, vol. 31, no. 5, pp. 1421-1435.
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In this study, effects of two types of geofibers, namely polypropylene and recycled carpet, on three dimensional shrinkage properties of cement treated kaolinite and bentonite clays are investigated. Cement treated clay specimens were prepared with cement contents of 5, 10, and 15 % by weight of dry soil for kaolinite samples, and 30, 40 and 50 % for bentonite samples. To investigate and understand the influence of different fiber types and contents, three different percentages of fiber content (i.e. 0.1, 0.2 and 0.5 % polypropylene fibers; and 0.5, 0.75 and 1 % carpet fibers) were adopted. The results of shrinkage tests on 126 cylindrical samples of cement treated clay with various cement and fiber contents were analysed to understand the relationships between these parameters and the shrinkage percentage of treated soil. Results of this study indicate that combination of cement and fiber is effective in reducing the volume change of clayey soils undergoing drying process. In the applied ranges of cement and fiber contents, the influence of cement addition on the shrinkage reduction is more significant than the addition of fibers for the treated kaolinite. However, addition of fibers in curtailing the shrinkage of bentonite clay is more significant than the cement addition.
Fatahi, B. & Khabbaz, H. 2013, 'Optimising The Pattern Of Semi-Rigid Columns To Improve Performance Of Rail Tracks Overlying Soft Soil Formation', Australian Geomechanics Journal, vol. 48, no. 3, pp. 89-97.
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With Australia facing a rapid increase in population in the next 30 years, the government is being proactive in handling the forecasted growth. The release of 201 0 Metropolitan Transport Plan by the New South Wales (NSW) Government shows that the State ofNSW will see an increase in commuter travel by rail. The NSW rail system is one of the most complex networks in the world and due to population growth, the network will require further expansion with construction of new railway lines partly on weak and marginal ground and win also require more frequent train running on existing lines. This study seeks to identifY the effectiveness of semi-rigid inclusion ground improvement techniques particularly stone columns and deep soil mixing in controlling settlement of soft soils when placed under the dead loads of the rail structure and the large live loads of freight trains. The employed numerical study assesses the relationship between the column position in the track cross section and the overall settlement of the ballasted rail formation. The numerical results show that the overall settlement of the track reduces significantly with the use of columns close to the centre of the track and not just under the rail. In addition, application of one layer of geogrids between sub-ballast and sub-grade assists to reduce the maximum settlement of track decreasing the future maintenance costs.
Fatahi, B. & Khabbaz, H. 2013, 'Influence of fly ash and quicklime addition on behaviour of municipal solid wastes', Journal Of Soils And Sediments, vol. 13, no. 7, pp. 1201-1212.
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Many closed municipal solid waste landfill sites are near urban areas and there are high expectations to improve geotechnical properties of these sites for re-development. Construction on closed landfill sites is generally a challenging task due to compl
Fatahi, B., Khabbaz, H. & Fatahi, B. 2012, 'Mechanical characteristics of soft clay treated with fibre and cement', Geosynthetics International, vol. 19, no. 3, pp. 252-262.
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In this study, the influence of three types of fibre; polypropylene, recycled carpet and steel, on the mechanical properties of cement-treated clay is investigated. Cement-treated clay specimens were prepared with cement contents of 5%, 10% and 15% by weight of dry soil, and cured for 14 days. To investigate and understand the influence of different fibre types and contents, three different percentages of fibre content were adopted. The results of unconfined compression tests on 90 cylindrical samples of cement-treated clay with varied cement and fibre contents are analysed to discern the relationships between these parameters and the key mechanical properties, including unconfined compressive strength and stiffness of treated soil. Furthermore, indirect tension test results of a further 90 treated soil samples have been used to determine the influence of fibre and cement content on the tensile strength of the treated soil. The fibre reinforcement increases the peak compressive strength. The addition of fibres increases the residual strength and changes the brittle behaviour of the cement-treated clay to that of a more ductile material. The tensile strength of the cement-treated clay is increased by adding carpet and steel fibres, but small quantities of polypropylene fibres do not influence the tensile strength.
Fatahi, B., Basack, S., Premananda, S. & Khabbaz, H. 2012, 'Settlement prediction and back analysis of Young's modulus and dilation angle of stone columns', Australian Journal of Civil Engineering, vol. 10, no. 1, pp. 67-78.
Ground improvement using stone columns is one of the most suitable methods for deformation control of soft soils. The use of stone columns can improve the bearing capacity, reduce settlement, accelerate consolidation process and enhance slope stability as well as resistance to liquefaction. Settlement prediction of the ground infl uenced by the large stiffness difference between the columns and the surrounding soil and the induced arching is discussed in this paper. Plate load test is one of the common methods to be used for quality control of stone column reinforced ground. The test results can be used to back calculate some of the design parameters of the stone column. A finite element based procedure to estimate the Young++s modulus and dilation angle of stone column material using plate load test results is proposed. The employed fi nite element model is axisymmetric and suitable for a cylindrical stone column. The field measurements after calibration have been in good agreement with numerical results for predicting deformations. The procedure developed in this study can be adopted by practicing engineers to estimate the Young' modulus and dilation angle of stone columns by conducting a plate load test.
Sadeghi Hokmabadi, A., Fatahi, B. & Samali, B. 2012, 'Recording inter-storey drifts of structures in time-history approach for seismic design of building frames', Australian Journal of Structural Engineering, vol. 13, no. 2, pp. 175-179.
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The growing trend in the application of direct displacement-based or performance-based design, lays more emphasis on the precise prediction of design parameters such as the inter-storey drift controlling the performance level of the structure. Practising engineers employ different methods to record the inter-storey drifts in time-history approach mainly based on the maximum lateral deformation of the structure. In this study, a 15-storey concrete moment resisting building is designed using time-history analysis. Then reliability and accuracy of each method in predicting the maximum inter-storey drifts under the influence of three earthquake records, namely 1995 Kobe, 1994 Northridge and 1940 El Centro earthquakes, are investigated. Results clearly indicate that to choose the most critical drift to evaluate the performance level of structures, the absolute maximum drift over time should be calculated. Other methods based on the maximum storey deflection may result in unconservative design.
Le, T., Fatahi, B. & Khabbaz, H. 2012, 'Viscous Behaviour of Soft Clay and Inducing Factors', Geotechnical and Geological Engineering: an international journal, vol. 30, no. 5, pp. 1069-1083.
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As a result of the scarcity of land for construction, a number of projects to construct manmade islands or to expand lands over soft grounds keeps increasing. Creep behaviour of soft ground has been considered as a challenging issue for engineers and researchers for many years. A number of studies have focused on the method to predict the creep deformation of the ground under a construction site. However, there is no unified theory to clearly explain the mechanism of soil creep deformation of soils. Results of the critical review in this paper indicate that the causes of soil creep can be categorised into five main groups, namely (a) the breakdown of the interparticle bonds, (b) sliding between the soil particles, (c) water flow from micro-pores to macro-pores (d) the deformation due to the structural viscosity and (e) the deformation due to the jumping of bonds. This paper presents these mechanisms in details with an effort to recommend an enhanced explanation for the creep compression mechanisms of clays.
Fatahi, B., Le, T. & Khabbaz, H. 2012, 'Effects Of Initial Stress State On Performance Of Embankments On Soft Soils', Australian Geomechanics Journal, vol. 47, no. 3, pp. 77-88.
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Analysing the behaviour of soft soil under embankment loads is a challenging task for geotechnical engineers. This numerical study revisits the case study of an embankment constructed on Boston Blue Clay, considering the model incorporating the influence of soil creep on the ground lateral defonnation and pore water pressure. Then a numerical parametric study is conducted to investigate the influence of the lateral earth pressure coefficient at rest (Ko) calculated on the different available correlations on the vertical and horizontal displacements, pore water pressures, and the of safety of the embankment. The results indicate that although the value of Ko influences the predicted horizental and vertical displacements notably, it has minor effects on the predicted pore water pressures. The lateral earth pressure coefficient influences the long term stability of the embankment and thus the effects of the initial stress field on the stability of embankments should be taken into consideration, while assessing the perfonnance of embankments constructed on soft soils. It is recommended to determine the in situ horizontal stresses using accurate methods such as self-boring pressuremeter to predict the behaviour of embankments on the soft ground precisely.
Tabatabaiefar, S., Fatahi, B. & Samali, B. 2012, 'Finite Difference Modelling Of Soil-Structure Interaction For Seismic Design Of Moment Resisting Building Frames', Australian Geomechanics Journal, vol. 47, no. 3, pp. 113-119.
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The importance of Soil-Structure Interaction (SSI) both for static and dynamic loads has been well established and the related literature spans at least 30 years of computational and analytical approaches for solving soil-structure interaction problems. Since the 1990s, great effort has been made to substitute the classical methods of design by new ones based on the concept of performance-based seismic design. Also, the necessity of estimating the vulnerability of existing structures and assessing reliable methods for their retrofit have greatly attracted the attention of engineering comunities in most seismic zones throughout the world. In the present study, in order to draw a clear picture of soil characteristics effects on seismic response of moment resisting building frames, a ten storey moment resisting building frame, resting on shallow foundation, is selected in conjunction with three soil types with shear wave velocities less than 600 m/s, representing soil classes Ce, De and Ee, according to Australian Standard AS 1170.4. The structure is modelled considering the three mentioned types of the soil deposits employing Finite Difference approach using FLAC 2D software. Fully nonlinear dynamic analyses under influence of different earthquake records are conducted, and the results of the different cases are compared and discussed. The results indicate that as shear wave velocity and shear modulus of the subsoil decrease, inter-storey drifts and subsequently the necessity of considering SSI effects in seismic design of moment resisting building frames increase. In general, by decreasing the subsoil stiffness, the effects of soil-structure interaction become more dominant and detrimental to the seismic behaviour of moment resisting building frames. These effects substantially alter performance level of the building model resting on soil classes De and Ee from life safe to near collapse. Consequently, structural safety for the mentioned building frames could not be ensured by employing the conventional design procedure excluding SSI.
Sadeghi Hokmabadi, A., Fakher, A. & Fatahi, B. 2012, 'Full scale lateral behaviour of monopiles in granular marine soils', Marine Structures, vol. 29, no. 1, pp. 198-210.
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Monopiles are used in piers as mooring or berthing dolphins. This article reports the results of full-scale lateral loading tests on monopiles constructed as dolphins in the Pars Special Economic Energy Zone in southern Iran. The length and diameter of the monopiles were approximately 40 m and 2 m, respectively. Lateral loading tests of such large monopiles are not commonly undertaken, thus there is limited data available. This research developed a lateral analysis of piles computer code to examine analytical methods for pile analysis. Appropriate models were introduced resulting in accurate predictions in the analysis of lateral loaded piles. The results showed that traditional p-y curves and strain wedge models calculate larger pile head deflection in comparison to the field test data and therefore local calibration is essential.
Fatahi, B., Khabbaz, H. & Basack, S. 2011, 'Effects Of Salinity And Sand Content On Liquid Limit And Hydraulic Conductivity', Australian Geomechanics Journal, vol. 46, no. 1, pp. 67-76.
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Soil conditions of construction sites have become worse than ever due to the overpopUlation in the metropolitan areas throughout the world. Likewise, the prevention of environmental risks due to individual activities is one of the most important subjects in the geo-environmental problems. Saline soils may induce several problems in geotechnical engineering projects such as infrastructure embankments, road construction and clay liners. Effect of the various concentrations of sodium chloride (NaCl) on several different soils including bentonite, kaolinite and fine sand mixtures has been evaluated. In addition, influence of salinity and the period of submergence on the hydraulic conductivity of soil samples collected from a certain area of east coast of India was investigated. The results show that the liquid limit of the mixtures generally decreases with an increase in the salt concentration. liquid limit decreased significantly with an increase in NaCl concentration up to a certain level. However, a further increase in the concentration does not induce any significant decrease in liquid limit. Furthermore, the soil hydraulic conductivity increase with the salt concentration and with increase in the period of submergence, the hydraulic conductivity of the soil increases asymptotically.
Sadeghi Hokmabadi, A., Fakher, A. & Fatahi, B. 2011, 'Seismic strain wedge model to analyse single piles under lateral seismic loading', Australian Geomechanics Journal, vol. 46, no. 1, pp. 31-41.
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One of the most effective methods of analysing a single pile and pile groups under lateral loading is Strain Wedge Model (SWM). SWM has a number of advantages in comparison with traditional p-y curves, but this model could traditionally only be used to analyse piles under monotonic loads. In the present paper, SWM has been modified to consider dynamic lateral loading. Based on this new method, called Seismic Strain Wedge Model (SSWM), a computer code has been developed for lateral analysis of piles. Using this computer code, some case studies have been analysed and the results show good agreement with test data. This paper introduces SSWM as a simple and powerful solution to analyse piles under lateral seismic loading.
Fatahi, B., Engelbert, D., Mujic, S. & Khabbaz, H. 2011, 'Effects of preloading on soft clay improvement using deep soil mixing', Australian Geomechanics Journal, vol. 46, no. 3, pp. 63-71.
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Poor performing soils, particularly soft clays, are more prevalent around lakes and coastal environments, where demand for construction is generally higher. It is therefore critical that snitable ground improvement techniques be developed and refined to ensure these sites perform satisfactorily under applied structural loads. There is a clear trend in geotechnical construction to further develop technologies such as Deep Soil Mixing (DSM), using cement, lime, fly ash or bottom ash, with an aim to improve the mechanical properties of problematic soils. In this study, the influence of surcharge (10 kPa to 120 kPa) applied during curing on soil-cement columns is investigated using two different clay types, namely kaolinite and bentonite. Preload provides confinement and pre-compression during curing, which in tum increases the bearing capacity of the treated ground. The results of unconfined compressive strength tests are analysed to illustrate how the mechanical properties of the clays composed of differing cement content are influenced under varying surcharges applied instantly after mixing. The results indicate that mechanical properties of cement treated soft clays, including strength and stiffness can be enhanced through the application of surcharge immediately after construction, during the curing phase. This could potentially provide a cost effective and enviromnentally friendly alternative by reducing the required cement content being added to soil to achieve a given strength.
Fatahi, B., Khabbaz, H. & Ho, L.H. 2011, 'Effects of geotextiles on drainage performance of ballasted rail tracks', Australian Geomechanics Journal, vol. 46, no. 4, pp. 91-102.
Naturally soft soils are mostly found around coastal regions, where the construction of ballasted rail tracks is required to have a more thorough consideration regarding filtration. Any poor filter design on weak ground inevitably leads to a critical change in ballast characteristics. It is noticeable that such a change results in several issues including significant migration of finer particles about the subballast-subgrade iuterface and the deficiency of subballast filtration. These problems eventually reduce the drainage ability orthe rail sub-system and may cause severe damage which can only be remedied by frequent and costly track maintenance. It is therefore important that geosynthetics such as geotextiles are introduced to the rail track system as an additional filter layer, which is able to retain the desirable filtering characteristics. This paper investigates the impact of non-woven geotextiles on filtration behaviour of sub ballast in the laboratory, while adopting different granular filter (subballast) thicknesses varying from 0 mm to 50 mm. The research findings demonstrate a notable difference in the cumulative fine loss per unit volume within a given period of time between two distinctive tests - with and without geotextiies, thus emphasising the beneficial application of this geosynthetic material. Empirical estimation of permeability and properties of subballast, including grading curves after testing, are carefully carried out and the results are presented in this paper. The results indicate tbat the thickness of granular subballast can be significantly reduced by including geotextiles. This paper, in turn, evaluates the potential combination of the track substructure and geotextiles to achieve the optimum filter design and more importantly, alleviate the cost of track maintenance.
Fatahi, B., Khabbaz, H. & Indraratna, B. 2010, 'Bioengineering ground improvement considering root water uptake model', Ecological Engineering, vol. 36, no. 2, pp. 222-229.
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Bioengineering features of native vegetation are currently being evolved to enhance soil stiffness, slope stabilisation and erosion control. The effects of tree roots on soil moisture content and ground settlement are discussed in this paper. Matric suction induced by tree roots is a key factor, governing the properties of unsaturated soils, directly imparting stability to slopes and resistance for yielding behaviour. A mathematical model for the rate of root water uptake that considers ground conditions, type of vegetation and climatic parameters has been developed. This study highlights the inter-related parameters contributing to the development of a conceptual evapo-transpiration and root moisture uptake equilibrium model that is then incorporated in a comprehensive numerical finite element model. The developed model considers fully coupled-flow-deformation behaviour of soil. Field measurements obtained by the Authors from a site in Victoria, South of Australia, are used to validate the model. In this study, the active tree root distribution has been predicted by measuring soil organic content distribution. The predicted results show acceptable agreement with the field data in spite of the assumptions made for simplifying the effects of soil heterogeneity and anisotropy. The results prove that the proposed root water uptake model can reliably predict the region of the maximum matric suction away from the tree axis.
Fatahi, B., Khabbaz, H. & Indraratna, B. 2009, 'Parametric studies on bioengineering effects of tree root-based suction on ground behaviour', Ecological Engineering, vol. 35, no. 10, pp. 1415-1426.
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Using native vegetation to improve soil stiffness, stabilise slopes and control erosion is a rapidly evolving process. A theoretical model previously developed by the authors for the rate of tree root water uptake together with an associated numerical simulation is used to study the effects of a wide range of soil, tree, and atmospheric parameters on partially saturated ground. The influence of different parameters on the maximum initial rate of root water uptake is investigated through parametric and sensitivity analyses. Field measurements taken from previously published literature are compared with numerical predictions for validation. The rate of selected parameters such as potential transpiration and its distribution, suction at wilting point, the coefficient of permeability and the distribution of root length density are studied in detail. The analysis shows that the rate of potential transpiration increases the soil matric suction and ground settlement, while the potential transpiration rate has an insignificant effect on the distribution of soil suction. Root density distribution factors affect the size of the influence zone. Suction at the wilting point increases the soil matric suction and ground settlement, whereas the saturation permeability decreases the maximum soil matric suction generated. The analysis confirms that the most sensitive parameters, including the coefficients of the tree root system, the transpiration rate, the permeability of the soil and its suction at the wilting point should be measured or estimated accurately for an acceptable prediction of ground conditions in the vicinity of trees.
Fatahi, B., Indraratna, B. & Khabbaz, H. 2007, 'Soft Soil Improvement Induced by Tree Root Suction', Australian Geomechanics Journal, vol. 42, no. 4, pp. 13-18.
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Indraratna, B., Fatahi, B. & Khabbaz, H. 2006, 'Numerical analysis of matric suction effects of tree roots', Proceedings of Institution of Civil Engineers, Geote..., vol. 159, no. 2, pp. 77-90.
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The use of native vegetation in the coastal regions of Australia has become increasingly popular for stabilising railway corridors built over expansive clays and compressive soft soils. The tree roots provide three tabilising functions: (a) they reinforce the soil; (b) they issipate excess pore pressures; and (c) they establish sufficient matric suction to increase the shear strength. The matric suction generated within the tree root zone propagates radially into the soil matrix, as a function of the moisture content change. Considering soil conditions, the type of vegetation and atmospheric conditions, a mathematical model for the rate of root water uptake is developed. A conical shape is considered to represent the geometry of the tree root zone. Based on this model for the rate of root water uptake, the pore water pressure distribution and the movement of the ground adjacent to the tree are numerically analysed. Field measurements taken from the previously published literature are compared with the authors' numerical predictions. It is found that, given the approximation of the assumed model parameters, the agreement between the predicted results and field data is still promising. The study indicates that native vegetation improves the shear strength of the soil by increasing the matric suction, and also curtails soil movements.