Model test of failure mechanism of tunnel with flexible joint crossing active fault under strike-slip fault dislocation

Abstract

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.

Keywords

• tunnel engineering
• strike slip fault
• model test
• failure pattern
• articulated design