In order to study the mechanical properties of rock mass structural planes under cyclic action, a cooperative reinforced cyclic shear configuration is proposed on the basis of investigation of existing cyclic shear equipment. The main functions, equipment composition and technical indicators of the developed multifunctional cyclic shearing device for rock mass structural planes were introduced in detail, and a series of rock mass structural plane tests were carried out. The cyclic shearing device mainly includes three parts: test device, power system, control and acquisition system. The maximum normal compressive stress is up to 60 MPa; the maximum cyclic shear stress is up to 100 MPa. The maximum size of sample can be 150 mm×150 mm×150 mm; The equipment takes more into account the research needs of cyclic shear test of structural plane. The device is designed for various mechanical tests of rock mass structural plane, including uniaxial compression test, the normal cyclic loading and unloading test, the monotonic shear test under various control modes. More importantly, the variable path cyclic shear test of structural plane can be carry out by the equipment. The experimental data are collected smoothly and the curve is smooth, which proves the effectiveness and accuracy of the developed equipment. The cyclic shear tests of rock mass structural plane under multi-factor variables are carried out by using the device. The results show that: The mechanical properties of cyclic shear of the structural plane are closely related to the normal stress, the roughness of the structural plane, the cyclic shear rate and the cycle number. Combined with a three-dimensional scanner, the three-dimensional texture scanning of the sample before and after the test is carried out. Then their three-dimensional digital terrain was established. Finally, the progressive failure process and failure modes of the structural plane in the cyclic shear were studied. The relevant research results will provide technical support for the study of the mechanical failure mechanism and constitutive model of the rock structural surface under the action of cyclic loading.
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Open Access
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Tunnels are integral to transport infrastructure and often face the formidable challenge of traversing active fault zones during construction. The active fault zones indicate potential geological disturbances, leading to structural damage and posing a severe threat to tunnel safety. Therefore, this study aims to propose a method of resisting dislocation of tunnel based on the brittle buffer concept to enhance the structural integrity of tunnels when confronted with displacements induced by fault activities. The method involves strategically filling the space between the primary and secondary linings with brittle and compressible materials, which serve as buffers to absorb and mitigate localized displacements caused by fault activities, thus protecting the tunnel from substantial damage.
To rigorously study and validate the effectiveness of the proposed brittle buffer structure in resisting fault displacements, a comprehensive indoor model experiment was designed and implemented. Scaling down the size according to a 40:1 geometric similarity ratio and using similar materials for the surrounding rock, lining, and buffer structures, tunnel model was cast in the laboratory, simulating fault movements within the model box. The analysis focused on the deformations and failure characteristics of the models under different fault loads, confirming the effectiveness of the brittle buffer structure.
Observations of tunnel deformation and failure modes after fault movements revealed distinct patterns. In the hanging wall of the fault, the brittle buffer structure at the arch top was crushed, accompanied by void formation at the arch bottom. Meanwhile, in the footwall of the fault, the arch top exhibited voiding, whereas the brittle buffer structure at the arch bottom was crushed. This deformation pattern effectively dispersed local shear deformations at the fault location, markedly mitigating damage to the lining. Impressively, under the protection of a 50-mm buffer structure, the lining model showed minimal damage even with a 100-mm displacement, equivalent to a substantial 4-m displacement in practical design scenarios, underscoring the robust performance of the brittle buffer structure in preserving the structural integrity of the tunnel. Furthermore, this study delved into strain monitoring data analysis and revealed a considerable shift in the peak strain of the lining away from the fault crush zone. This strategic relocation of strain concentrations to areas farther from the fault indicated a substantial reduction in strain intensity within the fault zone and confirmed the efficacy of the brittle buffer structure in dispersing and minimizing localized damage.
The results confirm the practical feasibility and effectiveness of incorporating a brittle buffer structure in tunnel designs for scenarios involving fault-induced displacements. This design exhibits exceptional performance in resisting fault-induced displacements, particularly suitable for tunnels crossing fault locations with significant estimated displacements. The outcomes of this study provide a crucial theoretical foundation and practical guidance for tunnel designs that cross active fault zones. This research contributes to the selection of antidisplacement solutions in tunnel engineering, paving the way for innovative approaches to address seismic challenges in tunnel construction.
Open Access
Issue
Based on the fault crossing situation of Xianglushan tunnel of water diversion project, we conducted systematic monitoring and analysis of key mechanical characteristics of tunnel such as surrounding rock rupture pattern, lining damage pattern and crack development, strain distribution characteristics during faults dislocation simulation through indoor physical model tests, and thoroughly studied the damage form and failure mechanism of tunnel with flexible joint crossing active faults under strike-slip fault dislocation. In terms of the mechanism of the design parameters of the flexible joint tunnel to resist faulting, the effects of factors such as liner section length, liner thickness, tunnel diameter, angle between tunnel axis and fault zone, tunnel section form, and mechanical properties of liner materials on the fracture resistance of the flexible joint tunnels were studied in detail. The results of the study show: 1) When the tunnel crossing the active fault is not articulated, the damage pattern presents a combination of shear and bending damage under the fault dislocation, and the lining damage is severe with a phenomenon of peeling off. The tunnel section shows elliptical deformation, and the overall collapse trend is obvious. The damage range of non-articulated tunnel reaches 4Wf (Wf is the width of the fault zone) in this scenario. 2) When the articulated design is adopted in the tunnel crossing the active fault, the deformation of the tunnel shows S-shape under the fault misalignment. The damage of the lining structure is in the form of inter-segment rotation and misalignment, while the lining segments are relatively intact and less damaged. The damage range of the flexible joint tunnel in this scenario is 2.14Wf, which is 48% less than that of the non-flexible joint tunnel, indicating that the articulated design can change the deformation and damage of the tunnel under the active fault dislocation and reduce the damage range of the tunnel structure. 3) Under the condition of articulated design, the maximum strain of the tunnel lining structure is mainly distributed in the fault zone, and the tunnel is prone to yield failure. Compared with the non-flexible joint tunnel, the maximum longitudinal tensile strain and compressive strain in the left and right side walls of the flexible joint tunnel are reduced by 56% and 68% respectively, which further indicates that the articulated design can effectively improve the tunnel’s resistance to fault dislocation. 4) In terms of the mechanism of the design parameters of the articulated tunnel, this paper concludes that the resistance performance of tunnel with flexible joint can be enhanced by increasing the tunnel lining thickness, increasing the concrete strength level of the lining, reducing the length of the section and reducing the diameter of the tunnel. The optimal angle of the tunnel through the fault zone is orthogonal, and the circular section can improve the resistance of the flexible joint tunnel compared with the horseshoe-shaped section. In summary, the research results can provide necessary theoretical reference and technical supports for the anti-faulting measures of cross-active fracture tunnel projects.
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