Cavity expansion in unsaturated soils exhibiting hydraulic hysteresis considering three drainage conditions

Abstract

SUMMARYCavity expansion theory assists in the interpretation of in situ tests including the cone penetration test and pressuremeter test. In this paper, a cavity expansion analysis is presented for unsaturated silty sand exhibiting hydraulic hysteresis. The similarity technique is used in the analysis. The soil stress-strain behaviour is described by a bounding surface plasticity model. Results of oedometric compression tests, isotropic compression tests and triaxial shear tests for both saturated and unsaturated states are used to calibrate the model. The void ratio, suction, degree of saturation and effective stress are fully coupled in the analysis. The influence of where the initial hydraulic state is located on the soil-water characteristic curve on the cavity wall pressure is investigated and found to be significant. Also, the effects of three different drainage conditions (constant suction, constant moisture content and constant contribution of suction to the effective stress) on cavity wall pressure are studied. It is found that the drainage condition in which the contribution of suction to the effective stress is constant offers a good approximation to the other two. This may simplify interpretation of in situ tests. When testing occurs quickly, meaning a constant moisture content condition prevails, a constant contribution of suction condition can be assumed without loss of significant accuracy. The contribution of suction assumed in the interpretation can be taken as being equal to the in situ value, although this discovery may not be applicable to all soil types, constitutive models and soil-water characteristic curves.

Exact solution for drained spherical cavity expansion in saturated soils of finite radial extent

“…Such a simplified model has also been adopted by Pournaghiazar et al and has been demonstrated to capture well the behavior in drained triaxial tests at large strains. The adopted constitutive model bear many similarities with that of Yang and Russell which originates from Russell and Khalili with minor modification on the compression line which is defined in a log e ~log p ′ plane. The adoption of the ln e ~ln p ′ plane is advantageous when the stresses relevant to the problem span a wide range, such as in cavity expansion .…”

The cone penetration test in unsaturated silty sands

“…Comparing the results for various net confining stress magnitudes reveals that the contribution of suction to cone penetration resistance becomes more significant as the confining stress decreases ( [14]). …”

“…The pressure at the wall of an expanding spherical cavity (σ L ) in a soil is related to the q c measured in a CPT. The findings of [14] for cavity expansions in unsaturated Lyell silty sand are adopted.…”

“…Also shown are the limiting isotropic compression lines (LICLs) determined using a range of laboratory compression testing ( [14]). Results for expanding spherical cavities in saturated Lyell silty sand under drained conditions are shown in Figure 4.…”

Pitfalls in interpretation of cone penetration test data recovered from unsaturated geomaterials

“…The same was not true for an unsaturated silty sand. Yang & Russell (2015 showed that the unsaturated silty sand behaved like a drained material. This is because the air in the pore space permitted volumetric compression to take place around a penetrating cone.…”