Resonant column apparatus tests and DEM analyses of intact and fractured rock specimens

This paper is to evaluate the rock dynamic properties and the effects of joints/discontinuities on wave propagation. To this end, laboratory tests are carried out in the Resonant Column Apparatus (RCA), a testing equipment usually adopted for soil dynamic testing. Particular attention is devoted to the determination of the shear modulus at small strains and the damping ratio of rock materials. Also, rock specimens with artificial joints with either smooth or rough surfaces are considered. Three-dimensional analyses with the Discrete Element Method (DEM) are performed to evaluate the experimental results obtained. The DEM model reproduces the testing equipment and mimics the RCA tests. The group velocity dispersion, occurring when a wave crosses a joint or a set of joints, is investigated by means of both RCA tests and DEM analyses. Measured and computed transfer functions are compared for all the specimens tested and considerations about the damping ratio are derived. A correction procedure is developed to estimate the rock dynamic properties by numerical simulations on aluminium specimens. The group wave velocity reduction, due to the presence of joints, as obtained from laboratory tests, is also analysed by the scattering matrix method.