Development of experimental technique on seismic response of rock joints

The application of a split Hopkinson pressure bar technique has been an active research topic to determine dynamic properties of rock materials, however, subjected of less attention on rock joints. One possibility is the configuration of long bars is especially suitable for the one-dimensional longitudinal wave propagation, which is difficult to investigate non-welded rock joints exposed to an obliquely incident wave, and further consider the frictional slip and the shear wave generation and propagation. The study discusses modified Hopkinson bars that conceive the design concept, and introduces a two-dimensional rock physical model to simulate a seismic wave across an inclined rock joint and allow the frictional slip and P- and S-waves propagation simultaneously. In the two-dimensional configuration, a granite plate as the specimen is mounted on an aluminum table. The table surface consists of half-buried balls, and the top of each ball contacts the polished bottom of the specimen to minimize the friction. An artificial rock joint is determined in 20 degree with respect to the front end of the specimen. A granite plate, with the same cross-sectional area as the specimen, is designed as the striker plate and immediately launched by a couple of identical springs to impact the front end and generate seismic wave. The specimen is pre-compressed by an axial compression system to make the plate subjected to coupled static and dynamic loads. Two groups of LVDTs are arranged perpendicular and parallel to the joint to measure its normal deformation and slip displacement, respectively. The incident, reflected and transmitted waves are recorded by two groups of strain gauge rosettes attached along the two sides of the joint, and the normal and shear stress distributions along the joint can be obtained.