SHEAR AND DILATION BEHAVIOR OF ROCK-JOINTS

Abstract

Strength characteristics of rock mass are greatly influenced by the presence of discontinuities. Intact rocks jointed in comparison of fractured rock mass shows high permeability, higher deformation characteristics and low shear strength along the plane of discontinuity. Thus the study of strength parameters becomes very important for the analysis of effect of joints on rock mass. In case of rough joint surfaces shear displacement is accompanied by vertical displacement or dilation and it is one of most important parameter which should be considered while designing any structure in jointed rocky strata. As it is very difficult to study the behaviour of actual rock joint in laboratory and field, artificial rock joint model are being used by researchers in order to estimate the behaviour of actual rocky strata. The aim of this research is also to study the shear and dilation behaviour of artificial regular rock joint (prepared by Plaster of Paris). Samples of rock- joints are prepared at an asperity angle of 15◦ and 30◦ of Plaster of Paris at a moulding water content of 50% by weight. Direct shear tests were conducted after 14 days of air curing under CNL condition in conventional direct shear machine. Shear stress offered and dilation measured for 30◦ asperity sample was more than that of 15◦ asperity sample at the same normal stress. It has also been noted down that peak shear displacement not only increases with normal stress for same asperity angle joint but also increases with increase in asperity angle at same normal stress. UDEC (Universal Distinct Element Code) was found suitable in predicting peak shear stress when compared conventional criteria’s given by Barton, 1973, Patton, 1966 as they are over predicting the results. When UDEC is compared with Barton-Bandis equation, 1981 and Asadollahi’s equation, 2010 for predicting peak shear displacement it has been found that UDEC is predicting comparable values while these equation are under predicting the result.