Volume change behavior of two compacted clayey soils under hydraulic and mechanical loadings

The paper presents an experimental study on the volumetric behavior of two compacted soils (Boughrara and Châtaignier clays) through suction-controlled drying-wetting and oedometric tests. During hydraulic loading (drying-wetting tests), the changes in void ratio, degree of saturation, and water content of both materials are plotted against the logarithm of suction, providing relatively comprehensive experimental results to validate recent empirical correlations on the wetting path and to derive the suction yield curve on the drying path. For mechanical loading (oedometric tests), volumetric changes are presented in the log10 (σv)-e plane, and an increase in yield stress and a monotonic decrease in compressibility coefficient λ(s) with suction are observed. These results show the suction hardening effect on soil stiffness, which is further illustrated by the analysis of the pore-size distribution curve. In addition, a new osmotic oedometric cell which takes advantage of the electrical resistivity technique is developed and used to measure the variation of degree of saturation and volumetric water content in oedometric tests, highlighting in particular how the hydraulic parameters change in a different way from the mechanical parameters (void ratio). The Barcelona Basic Model is examined and a new empirical correlation is proposed to determine the yield stress.