Investigation into shear performance of rockbolts under static and dynamic loading conditions

摘要

A large proportion of reinforcing elements in jointed rock mass can fail in shear. In the deep mines and rockburst-prone conditions, the bending and shear failure of rockbolts is also prevalent. This phenomenon has drawn greater attention and corresponding research has been conducted to investigate the shear performance of rockbolts. Nevertheless, the load transfer mechanism and the interaction between the rockbolts and rock mass were still not fully understood. Knowing both static and dynamic shear capacity of rockbolts and support systems is highly required to design the underground support rationally.The aim of this research is to provide a detailed analysis of shear behaviour of rockbolts using the laboratory tests and numerical modelling method approaches. Rockbolt and rock interaction, particularly near the shear joints, was investigated in this research. Four main parts were included in this thesis: static loading tests, numerical simulation under the static loading, dynamic loading tests, and numerical simulation under dynamic loading.A double shearing test (DST) system was used to examine the performance of rockbolt shearing. Testing was undertaken on certain strength concrete to simulate the rock mass. The laboratory test results reveal that rock strength, rockbolt diameters and installation angle, all affect the shear resistance of DST system by analysing the shear load-displacement relationships and the energy absorption abilities. It was found that rockbolts can increase the tension and shear properties of the surrounding rock mass. By comparing the DST results under static and dynamic loading conditions, it was found that the energy absorption ability of rockbolts is lower than under static loading condition. Thus, the dynamic performance of rockbolt is slight different with the static performance, which needs caution during the design of underground support in rockburst-prone condition.The numerical modelling technique was adopted to obtain the stress and strain developed along the bolt and surrounding materials under the shear load. FLAC3D was used for the static double shear tests, and ABAQUS Explicit was used for dynamic double shear tests. Parametric studies were investigated by the numerical simulation methods. This compensated the disadvantage of laboratory study, and could determine the commonly-used size of rockbolt performance that was not achieved in a laboratory study.