A New Model to Predict Mudstone Failure Behavior from Brittle to Ductile Caused by Confining Pressures

Understanding the failure behavior and mechanisms of mudstone is very important for engineering applications. While confining pressures play an important role in mudstone deformation, the limitations of laboratory conditions and mudstone sample preparation preclude scaled models of the mechanisms of deformation transition from brittle to ductile, especially for high confining pressures. In this study, dry indurated mudstone of the Kuqa depression in North China acted as the prototype rock for a numerical model. We performed numerical experiments for different confining pressures. Overall, the numerical model captured the stress–strain behavior and failure modes demonstrated by triaxial loading experiments from the laboratory at low confining pressures. Subsequently, the mudstone failure modes were predicted for high pressures. A new model to predict brittle–ductile failure behavior is proposed based on the understanding of the mudstone failure mechanism. The model showed the following. (i) For brittle failure stages, a shear dilatancy fracture is developed at low confining pressures. The rock failure modes undergo a high-angle shear fracture and a high-angle conjugate shear fracture. (ii) For brittle–ductile transition failure stages, a shear compaction fracture appears in rock deformation at high confining pressures. The fracture modes are exhibited as low-angle shear fractures and low-angle conjugate shear fractures.