EFFECT OF STRESS LEVEL AND EXCITATION SIZE ON COMPRESSION WAVES IN JOINTED ROCKS

M.S.CHA ¹ and G.C.CHO ²

¹ Graduate Student, Dept. of Civil and Environ. Eng., Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305 701, Republic of Korea

² Associate Professor, Dept. of Civil and Environ, Eng., Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305 701, Republic of Korea
(gyechun@kaist.edu )

The stress levels and the magnitude of excitation rarely affect elastic wave velocities in homogeneous media, such as an intact rock, while elastic wave velocities are more related to the magnitude of the excitation and stress level in particulate materials. Generally the wave velocity measured from the resonant frequency using steady state vibration decreases as the strain amplitude increases. However, a propagating compression wave front travels faster with increasing amplitude of source excitation in participate materials, steepening the shape of the wavelet front. The compression front increases the mean stress in the particulate materials, which affect the stiffness of the medium and the velocity of wave propagation, leading to shock waves. Shock wave propagation in rock masses induced by blasting or any large amplitude source has drawn attention in underground mining and civil engineering. Although the effect of the excitation magnitude and stress level on compression waves can be of concern in seismic investigation practices, adequate laboratory simulations for this phenomenon are rarely performed. Thus, this paper explores experimentally the effects of excitation magnitude and stress level on compression wave velocity in jointed rock...