Mechanical behavior and failure characteristics of rock with double holes

Abstract

Holes are common defects in underground engineering structures, which will reduce the strength and stability of surrounding rocks. Understanding the mechanical behavior and damage characteristics of specimens with holes under static loading is important to the safety of underground engineering construction. In this paper, PFC2D is used to study the mechanical properties and failure behavior of the specimens with double holes under uniaxial compression. First, the influence of rock bridge angle on the strength characteristics of the specimens was analyzed. The results show that with an increase in rock bridge angle, the peak stress and elastic modulus decrease first and then increase, and the curves approximately exhibit a ‘V’ shape. When the rock bridge angle is 45°, the peak stress and elastic modulus reach the minimum. Subsequently, the crack propagation, stress field evolution and crack closure mechanism of the double-hole specimens for different stress levels were investigated in detail. The results show that tensile stress concentration exist on the top and bottom of the hole, and compressive stress concentration exist on both sides of the hole in the initial loading stage. The crack initiation position is located near the hole and mainly in the tensile stress concentration area. 7According to the evolution of crack propagation, contact force chain and displacement field around the hole, three typical crack closure forms are proposed, which are mixed tensile and shear (type I), shear (type II) and shear (type III).