Correlation of granite rock properties with longitudinal wave velocity in rock bolt

Abstract

Physico-mechanical rock properties are typically investigated via laboratory tests using core samples. However, sample coring is time consuming and expensive. The longitudinal wave velocity in rock bolts embedded in a rock mass depends on the surrounding rock properties. Hence, the longitudinal wave velocity in rock bolts can be utilized to predict rock properties. This study presents the relationship between granite rock properties and longitudinal wave velocity (vL) in rock bolts to predict rock properties using the longitudinal wave velocity in a rock bolt. Chemical (saline solution) and mechanical (slake durability test) weathering processes are employed to diversify the properties of the rock specimens. Laboratory tests are conducted on rock specimens to measure the physico-mechanical rock properties, including the velocities (vp and vs) associated with constrained and shear moduli, density (p), Young's modulus (E), Poisson's ratio (mu), and porosity (I), compressive strength (fc), and slake durability index (SDI). The measured rock properties are used in the rock mass model, and variations in vL in the rock bolt with different properties are investigated via numerical simulations. Results show that vp, vs, p, E, and fc are correlated significantly with vL (R2 > 0.9), whereas I and SDI are moderately correlated with vL (R2 > 0.7). However, a meaningful correlation between mu and vL is not obtained. The root mean square and mean absolute percentage errors are estimated to validate the correlation equations, and errors are not considered. Results of the t-test show that the calculated t-value is higher than the critical t-value, and the p-value is smaller than the significance level of 0.05, indicating that the correlation coefficient is significant. This study shows that the velocity of longitudinal waves in a rock bolt can be a useful indicator for predicting in-situ rock properties.