Nguyen, L, Fatahi, B & Khabbaz, H 2017, 'Development of a Constitutive Model to Predict the Behavior of Cement-Treated Clay during Cementation Degradation: C3 Model', International Journal of Geomechanics, vol. 17, no. 7.View/Download from: Publisher's site
Nguyen, L & Fatahi, B 2016, 'Behaviour of clay treated with cement & fibre while capturing cementation degradation and fibre failure - C3F Model', International Journal of Plasticity, vol. 81, pp. 168-195.View/Download from: Publisher's site
Crown Copyright © 2016 Published by Elsevier Ltd. All rights reserved. Soil treated with cement becomes brittle because its shear strength decreases rapidly in a post-peak state, which is why in recent years the inclusion of fibre into soil treated with cement has become an increasingly popular research area. This paper presents a constitutive model to simulate the behaviour of the fibre reinforced cement treated soil, referred to as the improved soil composite. In this model, a non-linear failure envelope was formulated to merge with the Critical State Line (CSL) of the reconstituted soil mixture at high levels of stress in order to capture the broken cementation bonds and ruptured fibre. A non-associated plastic potential function and a general stress strain relationship that includes the softening of the composite soil were also proposed to simulate the pre-and-post peak state. Moreover, many researchers focus on the addition of fibre into sand, soft clay, and sand treated with cement, whereas the behaviour of soft clay treated with fibre and cement requires further investigation. Hence, in this study a series of undrained triaxial tests were carried out on natural Ballina clay treated with cement and 0.3%-0.5% of fibre to determine how the amount of fibre and cement affects the behaviour of soft clay. SEM images were also analysed to study the structure of the improved Ballina composite at the micro-structural level. The laboratory results indicated that the combined effects of cementation and fibre reinforcement increased the shear strength and ductility of treated soft clay. Under triaxial conditions the peak shear strength of soft clay treated with cement and fibre increases dramatically due to the formation of cementation bonds and the bridging effect provided by the fibres, and the brittleness caused by the cementation bonds breaking also improves significantly due to the inclusion of fibre. However, when shearing at a high mean effective stress the ceme...
Treating soft clay with cement and fibre has become an effective ground improvement technique for
transport infrastructure. Application of recycled fibres in deep soil mixing columns in soft soil sections
of road and rail projects is being considered by designers and clients as an efficient technique.
However, the combined effect of cement and fibre at failure requires further investigation. As the
effective stresses increase to a sufficiently high stress, the effect of cementation is diminished due to
the degradation of cementation bonds and the fibre exhibits failure due to either complete pull-out or
breakage from the soil matrix. Thus, the failure envelope of the reinforced soil gradually merges with
that of un-reinforced soil at higher stresses. In this paper, a constitutive model is proposed to simulate
the behaviour of the cement treated-fibre reinforced soil based on the Critical State Soil Mechanic and
the Modified Cam Clay model. In particular, the proposed model captures the beneficial effects of
cementation and fibre reinforcement such as the improvement in strength and ductility while the
cementation degradation and the failure mechanism of the fibre are also considered. In addition, a
series of un-drained triaxial tests were conducted to verify the performance of the proposed model.
This paper concludes that adding fibre into the cement treated soil clearly improves its residual
strength, thus, a significant increase in ductility is observed and well simulated. In this study, by
modifying the mean effective stress to include the cementation degradation and the fibre failure
mechanism, the proposed model results in realistic prediction for the behaviour of soil treated with
cement and fibre.
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.View/Download from: Publisher's site
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 stressstrain 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 stressstrain 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.
Nguyen, L, Fatahi, B & Khabbaz, H 2016, 'A Novel Model to Simulate the Behaviour of Cement-Treated Clay under Compression and Shear', Proceedings for the Fourth Geo-China International Conference July 25–27, 2016 | Shandong, China, GeoChina International Conference, ASCE, Shandong, China, pp. 152-158.View/Download from: Publisher's site
© ASCE.Soft clay treated with cement shows an improvement on strength due to the chemical interaction between cement and clay particles. Laboratory results showed that the peak strength of the cement treated clay reduces as the mean effective stress increases due to the effect of cementation degradation. Therefore, in this paper, a constitutive model was developed to simulate the behaviour of cement treated clay. Based on the critical state soil mechanics, the model proposed the non-linear failure envelope for the cement treated clay to merge with the critical state line (CSL) of the un-reinforced clay when the reinforced samples reach a sufficiently high stress levels. Moreover, a modified mean effective stress was proposed to include the contribution of cementation and its cementation degradation. Furthermore, the proposed model was evaluated by comparing the proposed model predictions against the Singapore clay treated with 10% cement available from the literature. The validation suggested that the proposed model can be used to predict the behaviour of cement treated clay very well.
Nguyen, L, Fatahi, B & Khabbaz, H 2014, 'Modelling Behaviour of Cemented Clay capturing cementation degradation', GEOTECHNICAL SPECIAL PUBLICATION NO. 238, GeoShanghai International Conference, American Society of Civil Engineers, Shanghai, China, pp. 168-177.View/Download from: Publisher's site
Nguyen, L, Fatahi, B & Khabbaz, H 2013, 'Predicting behaviour of cemented clay considering strength reduction due to high confining pressure', GeoMontreal 2013, GeoMontreal, Canadian Geotechnical Society, Montreal, Canada, pp. 1-6.
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.
Sri Ravindrarajah, R, Do, T, Nguyen, L & Aoki, Y 2010, 'Effect of clogging on the water permeability of pervious concrete', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australasian Conference on the Mechanics of Structures and Materials (ACMSM21), Australasian Conference on the Mechanics of Structures and Materials, CRC Press/Balkema, Melbourne, Australia, pp. 873-876.View/Download from: Publisher's site
Use of pervious concrete for pavement construction provides benefits such as reducing the stormwater run-off and recharging the ground water. This paper discusses the results of an experimental investigation into the effect of pore structure clogging and compaction on the water permeability of pervious concrete. The water permeability of pervious concrete was studied under falling head. The results showed that the clayey materials presence in the percolating water had seriously reduced the water permeability of pervious concrete. High-pressure water cleaning was found to partially recover the water permeability of pervious concrete. Since compaction causes pore structure modification, it should not be used with pervious concrete to ensure high water permeability of pervious concrete.