Effect of input signal type and time delay in sensors on wave velocity in rock specimens

Abstract

Accurate determination of wave velocity is critical to evaluating small-strain stiffness and helps identify anisotropy in rocks. The time delay in transducers and the selection of input signal types influence the computed wave velocity. Four types of input signals are used to obtain the travel time by determining the first arrival time and computing the peak-to-peak time for granite and sandstone specimens, and the phase velocity is computed by subtracting the time delay occurring in transducers from the travel time. The results show that the first arrival time and the peak-to-peak time tend to overestimate and underestimate, respectively, the velocity and a tone burst signal comprising a 5-cycle sine burst is most appropriate to gather the reliable velocity in laboratory-scale experiments. The estimation of anisotropy in granite and sandstone is well defined when a tone-burst signal is used. The accuracy of wave velocity measurement technique using first-propagated tone-burst signal is investigated by comparing the wave velocity measured by using reflected signals. The velocity measurement proposed by this study is useful to accurately estimated rock properties such as uniaxial compressive strength, poison ratio, elastic modulus, and shear modulus.