Failure mechanism of full-length grouted bolts for large-deformation tunnels under high geo-stress: A case study
Chaoguang Wu, Xianshun Zhou, Lichuan Wang, Zikun Li, Xuemin Zhang
Abstract
Maoxian Tunnel is located in a high-stress region and has undergone over 1.0 m of horizontal deformation, which has caused concrete cracking in the initial support and the failure of full-length grouted rock bolts owing to extrusion. Investigations revealed that higher water-cement ( w / c ) ratios lead to higher grout volume shrinkage ( V s ), consistency, and inadequate borehole filling. Combined with the lower compressive strength of grouting, this results in weak rock-bolt bonding. The wet contact interface further reduces the ultimate bearing capacity of the interface. Therefore, the rock bolts are squeezed out and fail. Reducing V s by adopting a smaller w / c ratio and optimizing the w / c agents can enhance the grout’s compressive strength. Additionally, the strength of the rock–bolt interface is improved in soft rock. The varying bolt length significantly influences the rock deformation control, but the tunnel stress relaxation in areas with high geo-stress extends beyond 8.0 m. Strengthening support structures and expediting installation are both crucial measures for resisting structural forces in such environments.