The effects of confining pressure on the post-yield deformation characteristics of rocks

Abstract

A research program into the dilatancy of Coal Measures and Coal Measures type rocks, deformed beyond the elastic rangep both up to, at and beyond the point of rupture, is outlined. Detailed descriptions of a 500 ton servo-controlled testing machine, and an apparatus for the laboratory measurement of volumetric strains in rock are given. The results of triaxial, compressive tests, conducted on specimens of seven rock types, compressed axially to strains in excess of ten percent, using this equipment, are presented. A review of the critical state model for soils is given, and a similar model for rocks is proposed, based on the experimental results obtained. The application of the measured volumetric changes of the rocks to the prediction of roadway closure, using yield zone analysis, is considered and the limitations of such analyses when considering stratified deposits discussed in conjunction with several case studies.