Geomechanics model test and numerical simulation of 2G-NPR bolt support effect in an active fault tunnel

Active faults are a common adverse geological phenomenon that can occur during tunnel excavation and has a very negative impact on the construction and operation of the tunnel. In this paper, the grade IV rock surrounding the cross-fault tunnel with poor geological conditions has been chosen for the study. The support capacity of 2(nd) Generation - Negative Poisson's Ratio (2G-NPR) bolt in an active fault tunnel has been carried out on the basis of relevant results obtained from the geomechanical model test and numerical investigations of failure model for existing unsupported fault tunnel. The investigation shows that surrounding rock of the tunnel is prone to shear deformation and crack formation along the fault, as a result, the rock mass on the upper part of the fault slips as a whole. Furthermore, small-scale deformation and loss of blocks are observed around the tunnel; however, the 2G-NPR bolt support is found to be helpful in keeping the overall tunnel intact without any damage and instability. Due to the blocking effect of fault, the stress of the surrounding rock on the upper and lower parts of the fault is significantly different, and the stress at the left shoulder of the tunnel is greater than that at the right shoulder. The asymmetrical arrangement of 2G-NPR bolts can effectively control the asymmetric deformation and instability of the surrounding rock. The present numerical scheme is in good agreement with the model test results, and can reasonably reflect the stress and displacement characteristics of the surrounding rock of the tunnel. In comparison to unsupported and ordinary PR (Poisson's Ratio) bolt support, 2G-NPR bolt can effectively limit the fault slip and control the stability of the surrounding rock of the fault tunnel. The research findings may serve as a guideline for the use of 2G-NPR bolts in fault tunnel support engineering.