Stability of Multi-Jointed Roof Rock Beams in Large Underground Openings

The stability of long shallow underground openings depends mainly on the bearing capacity of the lowest roof rock strata. Such strata are usually jointed and may be considered as discontinuous rock beam or plate structures. Their mechanical behaviour has been studied in the past by considering the mechanical analogue of a three-jointed voussoir beam. Provided that the stiffness of the rock joints is high enough, existing analytical solutions may be used for the calculation of the mechanical parameters of the problem. However, roof rock beams usually are crossed with more than three joints which have further low stiffness values. For such beams no analytical solution exists and their mechanical behaviour has been examined numerically. In this paper, the mechanical behaviour of such rock beams is described and simple methodologies for the approximation of their mechanical parameters are presented Further, their stability against snap-through failure mechanism is numerically examined with a distinct element code.