双圆隧道围岩中两组非贯通节理主导的裂纹扩展行为OA

To investigate the mechanisms of crack propagation and evolution in the surrounding rock of twin-circular tunnels with two sets of joints,biaxial compression tests were performed.Red sandstone specimens with prefabricated double circular holes and fissures at varying inclination angles were used.Acoustic emission(AE)and digital image correlation(DIC)techniques were integrated to systematically study the crack propagation behavior.The results show that the spatial angles between the left and right flaw sets significantly influence crack coalescence patterns and final propagation paths.Anti-wing cracks and oblique secondary cracks primarily facilitate connectivity between flaws,as well as between holes and fissures.The failure path of the multi-flaw system is governed by the weakest link,determined by the geometric morphology and relative positions within the flaw network.Prefabricated fissures significantly reduce the stress threshold for micro-crack initiation.The cumulative AE energy and stress curves display distinct characteristics,such as step-like increases or sharp rises near the peak stress,which reflects a transition in failure mode from sudden to progressive damage.This shift progresses from a tension-dominated mode to a mixed tension-shear mode as the defect complexity increases.In specimens with double holes and six fissures,tensile cracks account for less than 50%of the total,indicating a significant increase in the role of shear mechanisms.This study provides valuable insights into the failure mechanisms of surrounding rock in twin-circular tunnels under complex joint conditions.