STUDY OF STRENGTH CHARACTERISTICS OF ROCK

Abstract

Rock formations generally occur in triaxial state of stress with a wide range of confining pressure depending upon depth. For the stability analysis of an under ground excavation, foundation of high concrete gravity dams, rock slopes, power projects etc, "fie stresses in rock mass and the strength of rock may play a vital role. Rock Mechanics finds application in mining as well as civil engineering works. The failure criteria used in the mining works can not be directly used in the Civil Enginering Works, however introduction of some modifications can make them viable for use in Civil Engineering Works. The objective of the present work is to examine the strength behaviour of fairly medium strength rocks Ferogeneous Sandstone, Quartz-arenite Sandstorie (having unconfined compressive strength 26.5 MPa and 29.5MPa respectively) and of Quartzite (having unconfined compressive strength 79.5 MPa) under confining pressure ranging from 2.5 to 10.0 MPa. It is found that in this range of confning pressure the increase in strength at failure with the increase in confining pressure is more than the increase in strength as obtained by Hoek and Brown's (1980) Criterion and Bieniawski (1974) Criterion. The modified values of various constants used in Hoek and Brown criterion and in Bieniawski criterion are suggested by the analysis of data with the help of Computer Programme (LST) of "Non Linear Least Square Technique". An attempt has also been made to correlate the values of shear strength (C' & 0') with confining pressure for each rock.