P-wave velocity measurements can be used to evaluate the rock mass quality. Multiple factors including joint spacing can potentially affect P-wave velocity. This paper explores P-wave velocity variations as a function of joint spacing in Andesite rock samples. Samples were collected from boreholes from a dam site under construction. Physical and lithological properties of the samples were determined; artificial joints of 2 and 5 cm spacing were also created in the samples. In order to perform measurements of the P-wave velocity in samples, transducers were attached to the both ends of the samples while applying the ultrasonic waves. The results show a good correlation between the wave velocity number of joints and their spacing. They indicate that the decrease of wave velocity depends primarily on the joint spacing rather than the number of joints.
