Seismic response of rock joints under obliquely incident wave

Seismic response of joints which are found to be ubiquitous in rock masses is of great interest to rock engineers, geophysicists and seismologists. In the past years, wave propagation across rock joints has been the subject of extensive theoretical and experimental investigations. However, so far, studies especially the experimental works were mainly focused on the one-dimensional issues, i.e. normally incident wave propagation across rock joints. For the obliquely incident cases which are more common in nature, the shear deformational behavior of rock joints is involved, wave alternation occurs and the following wave superposition in the adjacent materials is complex. These issues arouse broad concerns and give rise to the significance of related researches, and at the same time, bring great difficulties for realization of the corresponding laboratory experiments. Given this situation, as an extension of the previous studies, this thesis is targeted to investigate the seismic response of rock joints under obliquely incident wave. The research scope is not limited to the propagation characteristics of the seismic waves, but also covers the mechanical behaviour of the joints and the evolution of the stress/velocity fields in the adjacent rock materials. Specially speaking, analytical solutions for wave propagation across rock joints are first derived in the time domain. It is demonstrated to be effective to obtain reflected and transmitted waves under different incident waveforms without additional mathematical methods. The mechanical analysis along the joint in the derivation process provides an inversion method to obtain the joint properties from the emerged waves in the following experimental work. To understand the wave propagation in the vicinities of the joint under obliquely incident wave, the lag times among passing waves at an arbitrary point are determined based on the analyses on the beam paths. Afterwards, wave superposition is conducted according to the lag times among each wave to obtain the stress/velocity field in the adjacent materials. Meanwhile, based on the mechanical analysis on the wave front, an indirect wave separation method is proposed for laboratory experiments. A new setup including the impact loading system, the moving and confining frame and the data acquisition scheme is established, based on which laboratory investigation is conducted on the joints which are artificially made by filling the quartz sand layer with different thickness under three types of water content conditions. The stresses on the two sides of the joint are compared to verify the stress continuity assumption in the displacement discontinuity model (DDM). The deformational behaviour of the joints under different incident angles is investigated. It is found that both the normal and shear deformational behaviours become more compliable with the increase of the joint thickness. In light of the discrepancy found in the loading and unloading rates, a broken line model is proposed to describe the deformational behaviour observed during the tests. By comparing the reflected and transmitted waves emerged from the joints obtained by the theoretical analyses and experiments, it is demonstrated that the theoretical results based on the broken line model agree well with the experimental results.