Abstract

Recent advances, not only in fluid flow but also in soil mechanics, have allowed the understanding and forecasting of common engineering problems such as slope stability, soil shrinkage and soil collapse. However, owing to limited access to data or more sophisticated numerical tools, the modeling of soil behavior is usually carried out considering simpler constitutive models which cannot predict some important features of unsaturated soils. This study is focused on the numerical modeling of unsaturated soils, adopting four constitutive models based on theories of elasticity and plasticity. For each model, a numerical simulation of a circular footing resting over a soil that is subject to drying and wetting processes is analyzed. Through the comparison of results, it is possible to highlight the use of more sophisticated constitutive models for unsaturated soil behavior, particularly forecasting the phenomenon of pore collapse during wetting processes.

Highlights

  • Several developments in soil mechanics have been progressively generalized in order to incorporate the effects of new phenomena and new variables to fit real soil behavior

  • The soil mechanics theory was extended by the consideration of unsaturated soils in which the pore space is occupied by water and air

  • Such feature is different from the Barcelona Basic Model (BBM), in the case that the horizontal axis is given by the mean net stress that can be negative

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Summary

Introduction

Several developments in soil mechanics have been progressively generalized in order to incorporate the effects of new phenomena and new variables to fit real soil behavior. Fredlund and Morgenstern [4] proposed that, for a proper understanding of the shear strength of unsaturated soils, it was necessary to consider two independent stress variables: the suction and the net stress. Taking into account those variables, Alonso et al [5] introduced the Barcelona Basic Model (BBM) to represent both the strength and the deformability of unsaturated soils. A generalized effective stress that includes the suction effect on the soil mechanical behavior and allows the recovery of the effective stress concept in saturated conditions is adopted. The presented numerical tests highlight the key differences between relatively simple and more comprehensive models to represent the behavior of soil foundations under drying and wetting processes

Constitutive relations
Mechanical constitutive model
Fluid-flow constitutive model
Stress equilibrium equation
Solution
Numerical tests
Findings
Conclusions

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