Study of rock truss bolt mechanism and its application in severe ground conditions

Instability of underground excavations is an ever-present potential threat to safety of personnel and equipment. Further to safety concerns, in the event of failure, profitability may reduce significantly because of loss of time and dilution of the ore, raising the importance of support and reinforcement design in underground excavations both in civil and mining engineering.<br><br>The truss bolt reinforcement system has been used in controlling the stability of underground excavations in severe ground conditions and preventing cutter roof failure in layered rocks especially in coal mines. In spite of good application reports, working mechanism of this system is largely unknown and truss bolts are predominantly designed based on past experience and engineering judgement.<br><br>In this study, the reinforcing effect of the truss bolt system on an underground excavation in layered rock is studied using non-linear finite element analysis and software package ABAQUS. The behaviour of the rock after installing reinforcement needs to be measured via defining some performance indicators. These indicators would be able to evaluate the effects of a reinforcing system on deformations, loosened area above the roof, failure prevention, horizontal movement of the immediate layer, shear crack propagation, and cutter roof failure of underground excavations. To understand the mechanism of truss bolt system, a comparative study is conducted between three different truss bolt designs. Effects of several design parameters on the performance of the truss bolt are studied. Also, a comparison between the effects of truss bolt and systematic rock bolt on different stability indicators is made to highlight the different mechanism of these two systems.<br><br>In practice, site conditions play a vital role in achieving an optimum design for the reinforcement system. To study the effects of position of the bedding planes and thickness of the rock layers, several model configurations have been simulated. By changing the design parameters of truss bolt, effects of thickness of the roof layers are investigated and a number of optimum truss bolt designs for each model configuration are presented.<br>