The burst resistance mechanism of anchored rock using new energy-absorbing material

Abstract

Rockburst is a common disaster in deep underground engineering, which seriously impacts project construction safety. Understanding its causes and burst resistance mechanism is of significance for rockburst prevention and mitigation. We developed a new type of high strength, large elongation, and strong energy-absorbing material, and conducted comparative tests on both basic and anchored rock specimens with such material. We analyzed the rockburst process, energy release and peak stress of the rock, and force and deformation withstood by the energy-absorbing bolts. The experimental results show that the energy reduction rate of the rocks reinforced by energy-absorbing bolts is more than 80%, compared with that of the basic rock. The force exerted on the energy-absorbing bolts increases suddenly when the rockburst occurs, and the strength utilization rates of the energy-absorbing bolts under strain rockburst and impact rockburst conditions are 73.3% and 61.2%, respectively. Rockburst also causes non-uniform shear deformation of the anchor bolt. Based on the rockburst energy criterion, the peak stress of the anchored rock is 2.2 times and 2.5 times the uniaxial compressive strength of the rock, respectively, under strain rockburst and impact rockburst conditions. The energy required for rockburst is 396.0 and 478.4 kJ/m3, respectively. The energy-anchoring bolts can effectively reduce the likelihood of rockburst. The results can provide a reference for support design for burst-prone rock in underground engineering.

1. Introduction

As underground engineering projects progress deeper and deeper, the construction process is often faced with complex conditions such as high stress and strong disturbance [1−4]. As a result, dynamic geohazards such as rockburst from surrounding rock continue to occur [5−7], posing a serious threat to the project construction and the safe and efficient exploitation of energy resources. Understanding rockburst mechanisms and associated control techniques is foundational to rockburst prevention and mitigation [8−10].

In terms of using experimental study to understand rockburst mechanisms, WANG et al [11] conducted uniaxial cyclic loading-unloading tests on rocks, established the maximum stored elastic strain index, and predicted the possibility of rockburst. GONG et al [12] carried out uniaxial cyclic loading-unloading experiments on different rocks, established a peak-strength strain energy storage index, and assessed the tendency of rockburst. GAO et al [13] performed uniaxial compression tests on coal-rock composites and studied the relationship between the degree of burst and the elastic strain energy. ZHANG et al [14] conducted biaxial rockburst tests on granite, analyzed the rockburst process using various techniques including visible light image, acoustic emission, and thermal infrared, and revealed the initiation mechanism of rockburst. HUANG et al [15] carried out uniaxial compression experiments on coal-rock composites under different loading rates. They analyzed the influence of loading-unloading rates and stress paths on the occurrence of rockburst. These rockburst tests aforementioned are mainly conducted under uniaxial and biaxial stress conditions. Since underground rocks are in a triaxial stress state, true triaxial experiments with loading and unloading in the laboratory can more realistically replicate the in-situ change of stress state due to excavations of deep rocks.

Regarding experimental studies of rockburst using true triaxial apparatus, HE et al [16] categorized rockbursts into two types: strain rockburst and impact rockburst. They believe that strain rockbursts occur during underground engineering excavations, while impact rockbursts are caused by dynamic impacts such as blasting after the completion of underground engineering structure. Under this principle, they conducted a series of rockburst experiments to study the evolution of rockburst and the characteristics of microstructural damage and to clarify the mechanisms of rockburst [17−20].