Mechanical behaviour of expansive soils after several drying and wetting cycles

Abstract

This paper presents results from an experimental study performed on natural and compacted expansive soils in different loose and dense states using principally osmotic oedometers. The loose soils showed significant shrinkage, while the dense soils produced a swelling accumulation during the suction cycles. These cycles induced an equilibrium stage, which indicates an elastic behaviour of the samples under suction cycles. At the end of suction cycles, a loading/unloading test was performed on all samples at different constant suctions to define LC (loading collapse) yield curve as well as the newly defined SC (saturation curve) yield curve. Generally, the suction cycles for the looser soils approached the LC and SC yield curves while they became the same at the equilibrium state. For the denser soils producing the swelling strain accumulation, the unique LC and SC curves were activated together. Additionally, we found that at the equilibrium stage, both initially loose and dense samples presented the same mechanical parameters. In other words, the LC or SC yield curves superimposed for different initial states of the samples at the equilibrium stage. Moreover, these compression curves provided sufficient data to propose a simplified model for the mechanical behaviour of the swelling soils at the equilibrium stage.

Keywords:

• expansive clay
• swelling
• shrinkage
• cyclic test
• equilibrium stage
• mechanical behaviour
• modelling

Acknowledgement

One part of this work on the natural soil was carried out within the framework of the national research project: Analysis of Shrinkage-Swelling Phenomenon Influence on the Structures (ARGIC) financed by the French National Agency of Research (ANR).