Experiment and Failure Analysis of Rock-Like Material Affected by Different Excavation Depths

Yuan Tian,Xinyu Liu,Zhende Zhu,Yanxin He,Miao Chen

doi:10.1155/2021/6633367

Abstract

In order to increase the understanding of the strength and failure mechanism of rock mass during tunnel excavation, a series of uniaxial compression tests were conducted on mortar specimen with cracks and holes by using a rock mechanics servo-controlled testing system. And by monitoring the experimental process, the initiation, propagation, and coalescence process of cracks were observed and characterized. According to the experimental results, the influences of the excavation depth on the mechanical parameters and fracture characteristics of mortar specimens with single hole and the ones with single-hole crack were analyzed in detail. In the specimens with single hole, the peak strength decreases with the increase of hole depth, but the peak strain and elastic modulus have no obvious linear correlation with the hole depth. And the position and angle of initial crack change differently with the increase of the hole depth. The position of initial crack moves from the side of the hole to the top of the hole. When the hole depth exceeds 50%, the crack initiation angle is no longer inclined to the axial stress direction, but parallel to the axial stress direction. In the specimens with single prefabricated crack, the wing-shaped secondary cracks are generated at the tip of the precrack, and the antiwing-shaped secondary cracks are generated at the tip when approaching the peak stress. However, in the specimens with single-hole crack, no antiwing-shaped crack appears. And when the hole depth reaches 80%, two wing-shaped cracks appear at the precrack tip. One of the new wing-shaped cracks appears in the direction of the extension line of the precrack.

Highlights

Since the mining of the earth resources has a long history, coal and mineral resources at shallow depths have gradually been exhausted [1]
Yang [4] conducted a series of uniaxial compression tests on red sandstone specimens with two prefabricated elliptical holes and analyzed the influences of the coplanar angle and ligament angle on the mechanical parameters and fracture process
In a large number of studies, in order to understand the mechanical properties and fracture characteristics of rock mass affected by excavation, the method of prefabricated hole and crack in rock-like material is usually used in the laboratory

Summary

Introduction

Since the mining of the earth resources has a long history, coal and mineral resources at shallow depths have gradually been exhausted [1]. Fakhimi et al [8] conducted biaxial compression tests on sandstone with single hole to simulate the failure of brittle rock during underground excavation In this experiment, the axial force and displacement were monitored, and microcracks were detected by acoustic emission technology. Researchers have conducted many experimental studies, using optical microscopes [12], the scanning electron microscope [13,14,15], the acoustic emission detection methods [16,17,18], the X-ray CT images [19, 20], and other different technologies to reveal the fracture process and the failure mechanism of microcrack propagation. In a large number of studies, in order to understand the mechanical properties and fracture characteristics of rock mass affected by excavation, the method of prefabricated hole and crack in rock-like material is usually used in the laboratory. Laboratory uniaxial compression tests were conducted to obtain the strength and deformation characteristics of the tunnel rock mass that change with the vertical load

Experimental Material and Loading Procedure

Discussion

Findings

Conclusions