A new high-pressure triaxial apparatus for inducing and tracking hydro-mechanical degradation of clayey rocks

This paper presents the development of a new high-pressure triaxial apparatus specifically prepared for inducing and tracking the degradation of clayey rocks. Total suction—used to induce the hydraulic degradation—is applied with vapor transfer technique by controlling the relative humidity of air in contact with the material. The evolution of the degradation process along different hydro-mechanical stress paths is continuously tracked with bender elements, as well as with air or water permeability measurements on partially saturated or saturated states, respectively. Relevant test results on a low porosity clayey rock (Lilla claystone, Spain) are presented to evaluate the main capabilities of the new equipment. The results bring up the high sensitivity to water of the material, which is evidenced by the important reduction of shear wave velocity induced on first wetting and drying at low confining stress, as well as by the significant increase in the air permeability of the degraded material (around four orders of magnitude larger than the intact material). Test results also showed clear differences in the volume change and shear strength behavior of undisturbed, saturated, and degraded samples, highlighting the relevance of degradation on macroscopic behavioral features.