Estimating the degree of reinforcement of horizontally bedded roofs strengthened by non-tensioned,full-column grouted bolts

Summary Roof sag or convergence during mining of horizontally bedded strata is accompanied by relative shear displacements along the separation planes. These displacements and therefore the roof convergence can be reduced by mobilizing the shear stiffness and resistance of full-column, non-tensioned bolts installed across the layers. Ultimately, if sufficient bolts are installed, there would be a negligible difference between the deflection of the bolted layers and that of a single layer of the same total thickness.In this paper a limiting equilibrium method is presented for determining the degree to which ideal reinforcement is reached.A number of examples are used to illustrate the use of the method for estimating the degree of reinforcement of a given rock bolt pattern, or for determining the bolt pattern required to attain a required degree of reinforcement. Both uniform and non-uniform loadings of the roof strata are considered.