No abstract

The internal damage of red-bed soft rock induced by water is pervasive. The accumulation, growth, and localization of damage is a multi-scale process that can lead to significant strength loss in red-bed soft rock. Yet, research on the critical state of deterioration process considering multi-scale failure is limited due to high degree of system freedom. Renormalization group theory is an effective approach to find critical point of phase transition in a disordered system. To apply renormalization group theory in red-bed soft rocks, this article firstly analyzed their microstructures. Then, the granular unit model and stripy unit model are proposed to describe the self-similar characteristics of red-bed soft rocks. The calculation results based on renormalization group theory are consistent with the experimental results. The critical reductions of strength induced by water are 60% in light-yellow silty mudstone and 80% in grey silty mudstone. In addition, the critical state of damage propagation caused by stress is also studied and the analytical solution is derived. Results show that the renormalization group theory can effectively couple the micro damage and strength deterioration which provides guidance to the engineering.

The purpose of this article is to investigate the rheological deformation behavior of soft rocks subject to the combination of externally applied compressive pressure and water-softening effects. To achieve this goal, a series of mechanical tests on soft rocks were performed by using a customized meso-mechanical triaxial test system consisting of a bidirectional servo confining pressure loading subsystem and a water pressure chamber. The system has the capability of simulating the actual compressive stress and water environment of soft rocks in engineering practice. The experimental results show that, under compressive stresses, water-softening effects could significantly increase the deformation rate of the soft rocks, ultimately lead to a larger deformation of the rocks. To further understand the combination of compressive pressure and water-softening effects on the deformation behavior of the soft rocks, an elastoplastic damage model was developed. It shows that the model can reproduce the experimentally observed deformation behavior of soft rocks. In addition, it reveals that, with the rock–water interaction, the deformation process of the compressed soft rocks can be described as the change from the attenuation state to the steady state of rheological deformation.