Analysis of rockburst triggered by hard rock fragmentation using a conical pick under high uniaxial stress

Abstract

High excavation-induced stress concentration and strong mining/tunneling disturbance are prominent conditions in deep excavations, and often present a coupled process to induce rockbursts. This study aims to reproduce and shed light on the rockburst process triggered by hard rock fragmentation using a conical pick. A true triaxial test apparatus was used to apply confining stress and pick force on cubic rock specimen, where the real-time values of the stresses and pick forces were recorded. A high-speed camera system was equipped to shoot the processes of rock fragmentation and rockbursts. The size of fragments produced in rockburst was analyzed via image processing approach. The results show that the cuttability and the rockburst susceptibility of hard rock under high confining stress are correlated with strength parameter and brittleness index of the rock material. Rockburst process consists of three progressive steps: surface slabbing triggered by pick penetration, rapid ejection and violent burst of chips powered by high confining stress, and final shear failure. The mean size of fragments produced in rockbursts decreases as the rock brittleness increases, which suggests that higher rock brittleness will induce more intense rockbursts. Therefore, the precautions, such as timely backfilling of the adjacent mined-out areas, flexible and energy-absorbing rock supports, and pre-destress ahead of excavation, should be taken to prevent rockbursts in peninsula- or island-type hard rock pillar under high excavation-induced stress.