Brittle rock mass failure in deep tunnels: The role of infilled structural plane with varying dip angles

Filled rock discontinuities are commonly encountered in underground engineering excavations, and their mechanical behavior has a significant impact on the stability of surrounding rocks. However, their performance under three-dimensional stress conditions has rarely been explored in the past. In this study, we summarized the typical failure characteristics of filled structural planes in deep-buried tunnels and conducted laboratory true triaxial tests on granite specimens to investigate the effect of dip angle and infill thickness on the failure characteristics of high-stress brittle surrounding rocks. The study monitored the characteristics of vertical stress-displacement, acoustic emission, acceleration, and failure process of granite specimens during the loading process and revealed the failure mechanism of brittle rock masses under the influence of infill thickness and structural plane dip angle. The results showed that the dip angle of structural planes has a significant influence on the failure mode of rock masses in deep tunnels. There exists a critical range of dip angles, within which the rock mass undergoes shear slip failure along the pre-existing structural plane, manifested by rock spalling near the structural plane. Beyond this critical range, the rock mass experiences strain-type brittle failure, characterized by violent rock ejection. Furthermore, the filling of structural planes can change the failure mode of rock masses and lead to more severe damage when the friction coefficient of the structural plane falls below a specific threshold. Additionally, it was revealed that a perpendicular ejection force exists on the free surface of the rock mass under loading, which is approximately vertical to the normal direction and is the primary factor responsible for the formation of vertical parallel cracks within the rock mass. The findings of this work are of paramount importance for comprehending the failure characteristics of deep-buried tunnels containing infilling joints. •Triaxial tests on granite with a structural plane reveal impact of dip angle and infill thickness on brittle rock failure.•The dip angle of structural planes can significant affect the rock mass failure in deep tunnels.•When friction coefficient dips below a threshold, filling structural planes alters rock failure mode, intensifying damage severity.•Perpendicular ejection force during loading on rock mass free surface is the primary driver of vertical parallel crack formation