Design principle for truss-bolt system and its application to deep coal mine roof reinforcement

Abstract

From the view of the safety and economical problems, the controlling of stability for fractured surrounding rock roof is one of the principal problems for deep underground coal mining engineering. A theoretical design method of the truss-bolt system for reinforcing underground fractured rock roof in coalmines is presented. The mechanical analysis of the system is considered in the models for the tie-rods and inclined roof bolts as well as three upper and lower bounds. The arching actions exerted by lateral behavior of the inclined bolts in reinforcing cracked roof are analyzed. The global-resistance concerning the lateral and axial behaviors of the inclined bolts in a truss-bolt-supported roadway is examined by using the classical theory of nonlinear beam under bending and tension. Based on the mechanical models, the design formulas concerning the lateral forces of bolts, tensions of tie-rod in truss system are given; and the reinforcement behaviors have been proposed. The analytical formulas for both lower and upper bounds for truss pre-tightening forces are put forward. Furthermore, the analytical equations for designing axial forces and dimensions of bolts in the system are presented. In order to make the truss-bolt design intelligent and effective, computer-aided design (CAD) software codes for coalmine truss-bolt reinforcement are developed. A case study for Suncun coal mine roadway supporting engineering is presented. This coalmine is considered as one of the deepest underground coal mining projects with buried depth of 1310 m in China. The in-situ tests show that the fractured roof is reinforced effectively; and the validity of study is proved.