Prediction of Strength and Modulus of Jointed Rocks Using P-wave Velocity

Abstract

Strength and deformation characteristics of jointed rocks are important parameters for the design of many civil and mining engineering structures. These parameters are difficult to obtain from direct testing of jointed rocks; hence it is usual practice to derive them through indirect approaches. In the present study, an attempt is made to obtain rough estimates of strength and modulus of jointed rocks through P wave velocity. Jointed specimens of a model rock were prepared for laboratory testing. Joints at different orientations and comprising of different joint roughness coefficients were used (JRC $$=$$ 2–4, 12–14 and 14–16). Ultrasonic P-wave velocity and UCS tests were conducted on the specimens. The effect of joint orientation and joint wall roughness on P-wave velocity was studied. An index, Joint Factor was used to quantify the effect of joint attributes on strength and modulus of jointed rock. It was observed that P-wave velocity is closely linked with Joint Factor. This study suggests a correlation to obtain Joint Factor Jf from P-wave velocity. P-wave velocity may be measured in the field and Jf may be computed through the suggested correlation. The computed Jf may then be used to get the strength and modulus values of jointed rocks. Charts are also suggested to roughly assess the shear strength parameters, cmass and ϕmass of the jointed rock.