Predicting bed separation in roof rocks of rooms

Abstract

Recent years have seen much discussion [ 1-~] of the development of reliable methods for predicting the behavior of rocks and the selection of the parameters of supports for mining-out faces. The authors of these reports concluded that the rocks above workings usually begin to break up when there is a loss of continuity along various natural weakened points induced by shear or cleavage.The distinguishing feature of sedimentary rocks is the presence of weak links along the beds, which are largely responsible for the onset of the development of disintegration; in igneous and metamorphic rocks the weakened sites are block contacts, cracks, and various other defects.From the practical point of view it is important to know not only the sites of possible break-up of the rocks but also the sequence of the processes of further development of these disturbances. The latter must be used in calculating the support capacity of the roof rocks (delineation of the beds and bands, determination of the stresses induced by the additional load imparted by the superincumbent roof rocks, and determination of the interbed friction forces), in selecting the characteristics of the support and the mining system to be used for underground mining operations.For the case of a single room of rectangular cross section, in [ 5] it was shown analytically for the first time that the loss of continuity of weakened interbed rock contacts by shear begins above the wall of the room. Similar results have been obtained for cases of several contiguous rectangular workings [7, 8]. Nevertheless, there is still no method enabling us to investigate by the use of engineering-geologic data the discrete discontinuity of the solid rock and to predict by calculation the stages of development of bed separation in a stratum at weakened contacts and positions.This article deals with the criterial postulates for such a method.We examine a system of contiguous rectangular workings (rooms) (Fig. 1), for which the geometric dimensions (pillar, room spans), the characteristics of the geological cross section of the layered roof, and the mechanical indices of the contact are known. As a result of the calculation we need to determine the sequence of inception and development of bed separation cracks in the roof rocks.