Shakedown modeling of unsaturated expansive soils subjected to wetting and drying cycles

Hossein Nowamooz,Kai Li,Cyrille Chazallon

doi:10.1051/e3sconf/20160908007

Hossein Nowamooz, Kai Li + Show 1 more

Open Access

https://doi.org/10.1051/e3sconf/20160908007

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Abstract

It is important to model the behavior of unsaturated expansive soils subjected to wetting and drying cycles because they alter significantly their hydro-mechanical behavior and therefore cause a huge differential settlement on shallow foundations of the structure. A simplified model based on the shakedown theory (Zarka method) has been developed in this study for unsaturated expansive soils subjected to wetting and drying cycles. This method determines directly the stabilized limit state and consequently saves the calculation time. The parameters of the proposed shakedown-based model are calibrated by the suction-controlled oedometer tests obtained for an expansive soil compacted at loose and dense initial states, and then validated for the same soil compacted at intermediate initial state by comparing the model predictions with the experimental results. Finally, the finite element equations for the proposed shakedown model are developed and these equations are implemented in the finite element code CAST3M to carry out the full-scale calculations. A 2D geometry made up of the expansive soil compacted at the intermediate state is subjected to successive extremely dry and wet seasons for the different applied vertical loads. The results show the swelling plastic deformations for the lower vertical stresses and the shrinkage deformations for the higher vertical stresses.

Highlights

Unsaturated expansive soils contain clay minerals such as smectite with the high capacity of water absorption
The initial state is closer to the reversible line which need less suction cycles to obtain the equilibrium state
Several models are developed for the complex hydromechanical behavior of the expansive soils submitted to the successive wetting and drying cycles, but these models are based on the traditional incremental method in elasto-plasticity leading to a very large calculation time

Summary

Introduction

Unsaturated expansive soils contain clay minerals such as smectite with the high capacity of water absorption. Several authors [15,16,17,18,19] applied this method to study the cyclic mechanical behavior of soils They introduced a series of transformed internal variables to characterize the mechanical system and constructed a local geometry in transformed internal parameter plane to estimate the stabilized limit state and its associated plastic components. This direct determination of the steady solutions in shakedown analysis is able to replace classic step-by-step method and needs less model parameters. Finite element code, the plastic strain field and the inelastic displacement field are calculated for a 2D geometry consisted of the intermediately compacted expansive soil and subjected to successive wetting and drying cycles

Analytical modeling of expansive soils based on shakedown concept

Plastic Shakedown during suction cycles

Elastic behaviour at the equilibrium state

Calibration of the parameters for the shakedown-based model

Numerical simulation of the in-situ behavior of an expansive soil

Conclusion