P-Wave Velocity Calculation (PVC) in Rock Mass Without Geophysical-Seismic Field Measurements

Abstract

Ultrasonic studies have been used as low-cost, quickly updated, non-destructive techniques in geology and geo-technique. Conventional geophysical operations that allow measurements of wave velocity in rock mass are costly. In this study, we sought a strategy for calculation of wave velocity in rock mass without these field operations. The velocity of a wave in rock mass is a function of two major factors: the intact rock and joint properties. Wave velocity has the highest value in the intact rock, and decreases in the presence of joints, the poorer the conditions of the joints, the greater the decrease. Therefore, wave velocity can be predicted from a measurement of velocity in the intact rock and the properties of the joints. In this research, we first measured P-wave velocity in selected Andesite intact samples from the boreholes, and then measured the rate of effect of joint spacing, opening, orientation, infilling, and roughness on wave velocity by inducing joints in the rock. Afterwards, the orientations of the joints were recorded through surficial joint studies at 29 stations in field. Moreover, the characteristics of the underground joints (6,530 joints) were determined through geotechnical drillings along 9 boreholes (with a total length of 840 m). Finally, the velocity of the P-wave in the rock mass was calculated in field along the assumed profiles. For validation, we compared our velocity estimations with available field data along seven profiles with a total length of 644 m, coinciding with our assumed profiles. The calculated wave velocity and that measured through geophysical operation in field were in close agreement. Thus, wave velocity in rock mass could be computed at an approximation rate of about 10%.