Roof bolting patterns at three-way entry intersections

The problem considered is the analysis of a three-way mine entry intersection where entries intersect at right angles. A plane view of the right angle three-way intersection is shown. In the analysis entry widths were varied at 14, 20, and 26 ft. Pillars which consist of coal were assumed to be 40 feet wide. The idealized structural model of the region used in the finite element method is shown. The model consists of rock and coal which were assumed to be linearly elastic, homogeneous, and isotropic materials. Material properties used in the calculation are given. The coal seam of eight foot thickness was assumed to be 592 ft. below the surface. The model was divided into 512 three-dimensional hexahedron elements each of which has eight nodes and 24 translational degrees of freedom. The model thus contained 729 nodal points and 2187 degrees of freedom. The computer program NASTRAN developed by NASA was used throughout the analysis. The calculated results indicate that an arching zone is formed above a three-way intersection and a region of vertical tensile stress is developed over a short distance into the roof. The maximum tensile vertical stress and required shear resistance of a three way intersectionmore » are considerably larger than those of the four-way intersection of the same entry width. The tensile vertical stress and required shear resistance increases with decrease of angle of entry inclination. Thus the 30-degrees-inclined intersection is hardest to support among the cases examined. Suspension and reinforce methods of roof supports were studied. Preferable bolting systems for both methods are proposed.« less