Abstract
The stress-strain response of compacted silty sand with over-consolidated stress history often exhibit distinct peak stress before reaching the critical stress type of response when subjected to suction-controlled triaxial shearing. Such heavily consolidated soil also tends to simultaneously manifest initial compression which transitions into dilational type volumetric response. Modelling such strain-softening type response, especially emulating the smooth transition from peak to critical state is a challenge. In this paper a previously developed generalized plasticity constitutive model, called MPZ (Modified Pastor-Zienkiewicz) is fine-tuned and calibrated using a set of suction-controlled consolidated drained triaxial tests conducted on compacted silty sand specimens. Firstly, the saturated and unsaturated silty sand characteristics and the experimental test program are briefly introduced. Secondly, the calibration of each component of the constitutive model, namely critical state, dilatancy, peak state, loading direction, water retention curve and bounding function are briefly explained. Furthermore, the material parameters are estimated, model performance is displayed, and finally discussed. Preliminary simulations show that the MPZ model is able to mimic overall suction controlled triaxial test response of compacted silty sand decently well by taking into account the changes in density, pressure and suction. However, the peak states are not accurately modelled for low-high suction levels which needs further modifications in proposed model.
Highlights
The compacted soils remain in unsaturated condition almost throughout the year and suction plays a key role in obtaining the unsaturated soil response
Fig.1. shows the actual photograph of the double-walled triaxial equipment modified to accommodate the unsaturated soil testing that was used in conducting a series of suction-controlled consolidated drained triaxial tests following conventional triaxial compression (CTC) stress path
Generalized plasticity (GP) constitutive models are characterised by introducing the phenomenological features in a hierarchical manner, i.e., progressing from simple to complex models, acquiring generality as they are further developed
Summary
The compacted soils remain in unsaturated condition almost throughout the year and suction plays a key role in obtaining the unsaturated soil response. The over consolidated soils tend to show post-peak softening type stress-strain response accompanied by initial compression followed by dilation type volumetric response. Accommodating these two distinct and different types of stress-strain and volume change response in soil-models is a challenge for researchers. A generalized plasticity model, named MPZ (Modified Pastor-Zienkiewicz) [8,10], capable of reproducing unsaturated states is used to reproduce the response of suction-controlled consolidated drained triaxial experimental tests conducted by [7]. Both matric suction and net stress are constant throughout the strain-controlled shearing stage
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