Strength of weak floor strata beneath rock pillars

Abstract

A simplified method for stratified floor strata ultimate bearing capacity (UBC) assessing, in room-and-pillar mining conditions, is presented. The physical problem consists of the following two different cases of rectangular rigid pillar of size B×L resting on a two-layer floor system: (a) with the upper weaker layer of thickness H overlying a stronger, infinite rock deposit. It has been assumed that bearing capacity of floor strata may be analyzed as a shallow foundation problem, using the general bearing capacity equation given by Brinch Hansen with appropriate shape, inclination, and surcharge depth factors, or may be treated as a punching failure problem, particularly in a case of relatively strong upper stratum presence. A broad review of available analytical techniques did show that a finite thickness of the upper weaker layer causes a significant increment/decrement in its ultimate bearing capacity in comparison with homogeneous conditions. The proposed approach has been also validated by numerical modeling utilizing FLAC3D the finite difference computer code.