In tunnel engineering, it is important to understand the influence of schistose structure on the failure strength of chlorite schist. To explore the strength control factors of chlorite schist, this paper firstly analyzes the mineral composition and meso structure of chlorite schist of different weathering states. The results show that the mineral composition of chlorite schist is changed during the weathering process, and that chlorite is an anisotropic rock mass. Next, a series of uniaxial compressive tests were conducted on chlorite schist samples with different bedding angles (the angle between bedding plane and loading direction; θ=0°, 15°, 30°, 45°, 60°, 75°, and 90°), moisture conditions (dry and saturated), and weathering states (strongly weathered and weakly weathered). Based on the test data, the authors discussed the change laws of the rock strength with bedding angle, weathering state, and moisture condition. The main results are as follows: Chlorite schist is a low-anisotropy rock mass, whose compressive strength exhibited a V-shaped trend with the growing bedding angle; the schistose structure is the internal cause of the deformation and the anisotropic or transversely isotropic strength of the schist; the schistose structure is reshaped and further damaged by external factors (e.g. water softening and weathering effects) in engineering. The research findings help to improve the rock stability and support design in tunnel engineering.
In burst-prone deep underground engineering, seismic waves generated from a near-field ground motion event may play a critical role in causing localized rockburst damage. Accurate estimation of near-field ground motions around excavations is important for seismic hazard risk assessment and dynamic rock support design in underground engineering. During the excavation of an underground cavern, stress redistribution in the surrounding rock leads to the formation of damage zones, including the excavation damage zone (EDZ) and excavation fracture zone (EFZ). The poor properties of the rock in the damage zones cause the wave velocities of the rock mass to decrease and the dynamic wave interaction to change, thereby affecting the ground motions around the excavation. This paper studies the near-field ground motion behavior and reveals the control effect of the seismic wave velocity in the damage zones on the near-field ground motions by the aid of the finite fracturing source model (FFSSM). The research results provide a new knowledge of the influence of excavation disturbance on the ground motion distribution around the excavation, and provide new ideas for the seismic hazard risk assessment and prevention in underground engineering.
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