Propagation properties of stress waves in one-dimensional geo-block medium

Deep rock mass is a block-hierarchical structure. Pendulum-type wave ( wave) discovered in Russian deep mines is a new type nonlinear and elastic wave, which is induced by the motion of geo-blocks under external pulse (such as deep seismic, rock burst and confined nuclear explosion) and different from the traditional longitudinal or transverse waves. In order to confirm the existence of the wave, the propagation properties of stress wave in blocks medium as well as the influences of the block materials, dimensions and geo-structures are studied. Based on the multipurpose testing system developed by the authors, one-dimensional low-speed impact tests are carried out on six granite and cement mortar blocks and continuum block models with different characteristic dimensions, respectively. For both block and continuum models, three-dimensional acceleration amplitudes of each sub-block (measured points) increase almost linearly with the increase of the vertical impact energies. For block models, three-dimensional acceleration amplitudes of each sub-block attenuates exponentially (one order) with the increase of the disturbed sub-block, and the decay coefficients are independent on impact energies. The increasing impact energies only increase the amplitude of the spectral density, and have nearly no effect on the 3D local maximal frequencies. The more the number of the blocks and the larger the external pulse, the more obvious of the tendency that the dominant frequencies develop toward low frequency region. Through comparison of the model test data with the in-situ measurements (critical energy for emergence of wave, amplitude and velocity, and the maximum spectral frequencies, etc.), the low-frequency and low-velocity waves occurring in blocks models are validated as wave. Based on the analysis of spectral densities time histories of 3D accelerations of five block models, the frequencies corresponding to the local maximums of spectral density curves of three-directional acceleration time histories satisfy quantitative canonical sequences of , which extends the conclusions of in-situ tests. The effects of material and dimension of model blocks are not obvious, and the above laws are not validated by continuum block medium. Finally, the visco-elastic interlayer and rigid blocks, concentrated mass as well as elastic blocks analytical models are established for theoretical analysis of acceleration time histories. The calculate results agreed well with the test data, and the effects of the parameters of interlayer are discussed.