Structural healing and decay of sedimentary soft rock in triaxial slide-hold-slide process and its modelling

In order to investigate the thermo-hydro-mechanical behavior of rock masses over long periods of time, slide-hold-slide triaxial tests have been conducted on a sedimentary soft rock under several patterns of effective confining stress conditions and under several thermal conditions. The strength recovery was observed in the re-sliding process after the holding period especially when the confining pressure is relatively low. An elastoplastic model incorporating the healing and decay of the rock structure is proposed to describe the strength recovery in the re-sliding process. The proposed model is based on a critical state soil model and is formulated according to the following concept. Firstly, the effect of density on the stiffness and strength is considered by introducing the modified concept of the subloading surface. Secondly, as the healing of the stiffness and strength occurs together with the increase of the rock structure with the increase of the holding period, the structural healing is modeled by the upper movements of the normally consolidation line and the critical state line in the plane of mean effective stress and void ratio. Thirdly, the structure decreases with the development of plastic strain and this is modeled by the lower movement of the two state lines. Triaxial slide-hold-slide tests are simulated by the proposed model and applicability of the model is discussed.