Study of compressive strength of jointed rockmass

Abstract

Rock masses are hardly present in intact state in nature but are most commonly found in jointed form. In-situ test for determining the behaviour of jointed rock mass is costly and time consuming, hence attempts are being made by researchers to predict the strength and deformation behaviour of jointed rock masses under controlled laboratory conditions. Considering its implications experimental study has been undertaken for determining strength characteristics of jointed rock mass. Models have been prepared using plaster of paris and different degree of anisotropy have been induced by inducing joints in them at orientation (β) varying from 0° to 90°. The parameters studied are-
i) Variation of compressive strength ratio (σcr= σcj/σci) of Plaster of Paris under unconfined conditions with joint factor.
ii) Variation of jointed cohesion (Cj), friction angle Φj and roughness parameters r=tanΦj.
where, σcj = Uniaxial compressive strength for intact mass. σcj = Uniaxial compressive strength for jointed mass. n = Inclination parameter r = Joint strength The values for cohesion Cj for jointed specimen of Plaster of Paris was found to be 0.16 MPa and the value of friction angle Φj was found to be 39°. Hence the roughness parameter ( r= tan Φj ) comes out to be. 809 for the specimen of Plaster of Paris tested. The optimum value of uniaxial compressive strength (σ ci ) evaluated from the above test was found to be 11.00 MPa. Comparison also has to be made between the observed experimental values and the empirical relations given by various researchers previously.