Study on water–rock interaction failure mechanism and constitutive model of mudstone damaged by pre-peak disturbance

Abstract

The mudstone disturbed by engineering has been damaged to varying degrees before the peak strength, which is often ignored in the existing research. To reveal the failure mechanism and mechanical characteristics of mudstone under the combined action of water and damage. Firstly, this study proposed a pre-peak damage variable (Da) to characterize the degree of damage before peak stress. Then, triaxial tests were conducted to assess the mechanical properties under different Da and the water–rock interaction. The failure mechanisms of mudstone were revealed from both macro and micro perspectives. Finally, a statistical damage constitutive model for mudstone was constructed, and the rationality of the model was verified using experimental results. The results indicate: (1) The reduction of strength parameters caused by engineering disturbance and water rock coupling is the main reason for the instability of mudstone slope after construction. (2) Mudstone strength decreases gradually and then sharply with increasing Da. The Da reduces mudstone strength by 10%-20% on the original conditions. The Da firstly reduces the cohesion, and then the friction angle. (3) The undamaged mudstone mainly exhibits a multiple-failure-plane mode, while damaged mudstone consists of a single-failure-plane mode. The reason is that the damage zone of mudstone is more likely to infiltrate water molecules, leading to lubrication and softening of the mineral particle skeleton, resulting in a single fracture surface failure mode. (4) The constitutive model for mudstone considering the water weakening and Da effectively describes the stress–strain relationship of damaged mudstone under the water–rock interaction. The research provides new insights into the evolution of soft rock damage considering disturbances and water weakening.