Deformation characteristics of surrounding rock and reinforcement parameter design of weak interlayer tunnels

The Wugushan No.1 tunnel of Taijiao railway was monitored and the deformation characteristics of the surrounding rock of the weak interlayer tunnel were analyzed. Converting the mean values and standard deviations of mechanical response results of the surrounding rock and the support on multisection into the ECULID distance from the origin point on a two-dimension plane as evaluation indexes, the influence of the reinforcement parameters on the mechanical response of the surrounding rock and the support was analyzed by orthogonal experiments. Based on fuzzy decision theory, by using the ECULID distance between the simulated result of each group and the global optimal value of the multiple evaluation index as the comprehensive evaluation index, a reinforcement parameter design method was proposed. The mechanical response of the surrounding rock and the support of No.1 tunnel without grouting and with grouting using the optimal reinforcement parameter combination were respectively studied. The results demonstrate that the crown settlement of the tunnel has the characteristics of long duration, fast settlement and large final settlement. Grouting reinforcement can reduce about 70% to 80% of the crown settlement, shorten the stability time of the surrounding rock and effectively restrain the development of the surrounding rock displacement. Cohesive and shear strength have the most significant influence on the excavation response of the weak interlayer tunnel. In the non-grouting tunnel, a large bending moment and a non-negligible torque are produced at the intersection of the weak interlayer and the excavation section, and the concentrated stress occurs at the arch foot of the initial support, which makes the excavation stability of the tunnel is difficult to be guaranteed. No.1 tunnel was reinforced by grouting utilizing the reinforcement design method proposed in this paper, showing that the surrounding rock loose area is narrowed, the section torque is reduced to be negligible and the stress concentration of the initial support is positively improved. © 2021, Science Press. All right reserved.