Parsa-Pajouh, A, Fatahi, B & Khabbaz, H 2016, 'Experimental and numerical investigations to evaluate two-dimensional modeling of vertical drain-assisted preloading', International Journal of Geomechanics, vol. 16, no. 1.View/Download from: UTS OPUS or Publisher's site
© 2015 American Society of Civil Engineers. In this study, the efficiency of proposed formulations for plane-strain modeling of vertical drain-assisted consolidation was evaluated. For this aim, the vertical drain-assisted preloading process was experimentally simulated using a fully instrumented large-scale Rowe cell. Nine pore-water-pressure transducers were installed in various locations to measure the changes in pore-water pressure during the test. Two pressure/volume controllers were connected to an infinite-volume controller to provide continuous water flow. Soft clays with predefined properties were used to form the intact and smear zones. A numerical code was developed by using the finite-difference program FLAC 2D to simulate the consolidation test. A numerical study was conducted to evaluate the efficiency of the proposed solutions for converting the axisymmetric state to a plane-strain condition and was subsequently compared with corresponding numerical analysis. From the results, it is observed that some of the proposed methods resulted in more accurate predictions of settlement and changes of pore-water pressure in the early stages of the consolidation process, whereas other proposed methods performed more accurately in the later stages of consolidation. Thus, three-dimensional modeling with actual soil-permeability properties to simulate the time-dependent behavior of soft soil improved with vertical drains is recommended.
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.View/Download from: UTS OPUS or Publisher's site
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.
Parsa-Pajouh, A, Fatahi, B, Vincent, P & Khabbaz, H 2014, 'Trial Embankment Analysis to Predict Smear Zone Characteristics Induced by Prefabricated Vertical Drain Installation', Geotechnical and Geological Engineering, vol. 32, no. 5, pp. 1187-1210.View/Download from: UTS OPUS or Publisher's site
© 2014, Springer International Publishing Switzerland. In this study, FLAC finite difference software has been adopted to simulate the performance of the ground improved using prefabricated vertical drains assisted preloading, considering smear zone characteristics. The numerical code has been applied to predict smear zone properties employing a back calculation procedure using the results of several case studies. The construction of a trial embankment is proposed as a reliable method to predict the smear zone characteristics. The proposed back calculation method is applied to estimate the minimum required degree of consolidation and consequently the minimum required preloading time, resulting in a reliable estimation of the smear zone permeability and extent. Three preloading case studies considering both conventional preloading and vacuum assisted preloading have been simulated to verify the numerical code and to conduct the parametric study using the back calculation procedure. According to the results, the properties of the smear zone can be back-calculated reliably, when at least 33 % degree of consolidation due to trial embankment construction is achieved.
Parsa Pajouh, A, Fatahi, B, Khabbaz, H & Vincent, P 2014, 'Evaluating Proposed Solutions for Equivalent Plane Strain Modeling of PVD Assisted Preloading', Advances in Transportation Geotechnics and Materials for Sustainable Infrastructure (GSP 250): GeoHubei 2014, International Conference on Transportation Geotechnics (ICTG), ASCE, China, pp. 9-16.View/Download from: UTS OPUS or Publisher's site
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.
Parsa Pajouh, A, Fatahi, B & Khabbaz, H 2013, 'Numerical Analysis to Quantify the Influence of Smear Zone Characteristics on Preloading Design in Soft Clay', Challenges and innovations in geotechnics. Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, International Conference on Soil Mechanics and Geotechnical Engineering, Presses des Ponts, Paris, France, pp. 2573-2576.View/Download from: UTS OPUS
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.
Parsa Pajouh, A, Fatahi, B & Khabbaz, H 2011, 'Numerical Back Analysis of Smear Zone Properties for Vertical Drain Assisted Preloading in Soft Soils', ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, International Conference on Advances in Geotechnical Engineering, Curtin University, Perth, Australia, pp. 561-566.View/Download from: UTS OPUS
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.
Parsa Pajouh, A., Fatahi, B. & Khabbaz, H. 2010, 'Uncertainties of Smear Zone Characteristics in the Design of Preloading with Prefabricated Vertical Drains', The 4th International Conference on Geotechnical Engineering and Soil Mechanics (ICSESM 2010), International Conference on Geotechnical Engineering and Soil Mechanics, Iranian Geotechnical Society (IGS), Tehran, Iran, pp. 1-8.View/Download from: UTS OPUS
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.