Optimizing the reinforcement effect of full-column,untensioned, grouted bolts in bedded mine roofs

Summary The benefits of installing full-column, untensioned, grouted bolts in bedded mine roofs generally include a greater pull-out strength than mechanical, point anchor bolts, a greater axial stiffness, and a greater shear stiffness. The latter characteristic (dowel effect) is helpful in reducing shear slip along planes of separation in the roof and hence roof sag or convergence.This paper reports on analytical and model studies undertaken to determine if there is a positioning of grouted bolts across the span of the opening for which the dowel effect reaches a maximum or optimum value. A variety of loading cases is examined, including uniform and parabolic loading of roof beams resting on rigid or deformable abutments, and it is shown that there should be a greater density of bolts towards the ribs or sides of openings. The precise locations of the bolts for optimizing reinforcement are also shown to depend upon roof span, abutment thickness, elastic moduli of roof and abutment, and beam thickness.