Study on Long Wavelength Propagation of Seismic Waves Across Filled Joints Using Resonant Column Experiments

Wave propagation across a jointed rock mass involves transmission and absorption of energy at the joints presentin them. For assessing the modulus of a rock mass during dynamic loading, information on wave propagation across jointed rock mass is inevitable. Joints present in a rock mass can be either frictional joints or filled joints. Gouge materials may present in rock masses that exist at shallow depths and these rock joints are usually referred to as filled joints. The frequency of the incident wave is an important parameter that determines the wave velocities and the amount of energy transmitted across jointed rocks. In this paper, a study on long wavelength propagation of shear and compression waves across filled joints isconductedusing a resonant column apparatus with modifications to method of testing. Experiments were performedon jointed Plaster of Paris samples whose joints are filled with clay material of varying thicknesses. Modifications adopted tothe resonant column apparatus for testingstiffmaterials are explained in this paper. Shear and compression wave velocities were obtained for three different confining pressures.Damping ratios and attenuation coefficients were calculated for all thicknesses of clay material.Wave velocities and damping ratios under various strain levels were obtained and it could be observed that wave velocities get reduced whereas damping ratios get increasedeven with slight increase in thickness of clay material over various strain levels.