The seepage characteristics of fractured rock mass under compression and shear are one of the important factors affecting the stability of rock mass engineering. In order to understand the effect of shear action on the variation of joint surface aperture and reveal the mechanism of shear action on the seepage behavior of joint surface, in this paper, laboratory tests and numerical simulations were used to study the shear flow in the rough rock joints. Based on the results of shear tests in the laboratory, a numerical seepage model considering the contact mode of joints surface was established by introducing contact mode into the elastic deformation of rock, and the changing trend of the fluid flow characteristics in the shear process was studied. The results show that the numerical model can restore the stress distribution and contact region evolution, and the inhomogeneous distribution and evolution of the apertures are closely related to the distribution and evolution of the fluid flow velocity inside the fracture, with the area of higher flow velocity showing a distribution trend perpendicular to the flow direction. This model can be used to predict the effect of shear on rock seepage in underground projects with fracture surfaces under complex stress conditions, and it is a guide for the study of shear-flow models with rough connection surfaces.

Laboratory shear test is an important and widely used method to investigate the shear behavior of rock joints, and the preparation of joint specimens is a key factor that influences test results. In order to study the shear mechanism of rough rock joints with different morphologies in the laboratory, an innovative three-dimensional (3D) engraving technique was employed to produce specimens with rough joints. Intact sandstone and cement mortar blocks were used as model materials. The engraving parameters were determined to ensure a satisfactory engraving precision and to save as much time as possible for an engraving process. Three Barton profiles with joint roughness coefficient (JRC) values of 2.8, 10.8, and 18.7 were selected as the morphology prototypes for automatically engraving the model material blocks to obtain rough joint specimens. Shear tests were then conducted under four normal stress levels in the laboratory. In addition, numerical simulations on joints with the same physico-mechanical properties, surface morphology, and boundary conditions as the joint tested in the laboratory were performed. The failure characteristics, shear behavior curves, and shear strength obtained from numerical and experimental studies were analyzed considering the effect of joint materials, joint roughness, and applied normal stress. The shear mechanism of rough joints was investigated, and the analysis indicated that the results of shear tests by simulation and experiment were similar. The results revealed that it is feasible to make rough joints by engraving either real rocks or commonly used model materials (e.g., cement mortar).

Excavation in rock masses always encounters safety problems from rock fracture seepage in water-rich areas, which needs to be paid much attention, especially for fractured rocks under complicated stress state. For this reason, the permeability of fractured sandstone and granite is experimentally investigated under cyclic loading-unloading confining stress and axial stress. The variation of permeability coefficient and seepage flow with increasing and decreasing the confining stress and axial stress are comprehensively analyzed. Results show that the changing patterns of permeability with loading-unloading cycles of confining stress for both fractured sandstone and granite are similar. The permeability is most sensitive to the initial loading-unloading stages. After several loading-unloading cycles, the confining stress has little effect on permeability. The seepage flow decreases as the confining stress is unloaded to the same level in the loading process, indicating a hysteresis effect on the recovery of seepage capacity. The seepage properties under cyclic loading-unloading the axial stress are quite different from those under the confining stress. The permeability of fractured sandstone is most sensitive to the first cycle of loading-unloading of axial stress. The irrecoverable shear slide between fractures under the axial stress causes dilatancy or contraction, which makes the permeability coefficient to consecutively decrease at the subsequent cycles. The permeability of granite first decreases during the first loading of axial stress, while this trend is disordered at the subsequent stages no matter loading or unloading the axial stress. This is because of the accumulation of breakage fragments between fractures, which further disturbs the seepage flow. These findings may be useful for further understanding the seepage properties of fractured granite and sandstone under complex loading-unloading history.

The deformation control of surrounding rock is a crucial aspect in the design and construction of tunnels that traverse weak geological formations. This study developed a three-dimensional numerical model of tunnel excavation that accounts for the hysteresis of initial support, based on a highway tunnel under construction in Ganzhou, China. The rationality of the numerical model was verified through on-site measurements, and orthogonal tests were conducted to analyze the impact of construction parameters on the deformation of surrounding rock. The research findings indicate that the pipe-roof can be divided into four longitudinal sections according to the distribution of stress state: the tension section ahead of the entrance casing arch, the compression section behind the tunnel face, the tension section ahead of the tunnel face, and the compression section at the rear end of the pipe-roof. The grouting reinforcement can restrict the generation and development of plastic zone in the arch of surrounding rocks, which reduce the vault settlement significantly. The primary and secondary order of the impact on tunnel vault settlement, side wall convergence and surface uplift are excavation method, pipe-roof grouting radius, initial support thickness, pipe-roof layout range.