Experimental and numerical investigations on cross rock pillar method for super large cross-sectional tunnel excavation

To solve stability issues of super large cross-sectional tunnel with greater than 20 m across and an overall area greater than 314 m2 during excavation, a new technique named cross rock pillar method (CRPM) is proposed. A physical model test was firstly conducted to investigate the deformation and failure mechanisms of a tunnel using CRPM. In this physical model, a rock-like material simulating the V-class surrounding rock was made and a geomechanical model test bench was developed to simulate and observe the progressive failure process of the tunnel. Furthermore, fiber sensing technology was used to continuously monitor the horizontal strain in different cross sections. Test results show that the cross rock pillars play a significant role in preventing deformation of the surrounding rock during the tunnel excavation. A numerical model was then established to verify the results obtained by the physical model test. The deformation and stability mechanisms of the surrounding rock are determined using CRPM in super large cross-sectional tunnels. Finally, the proposed CRPM was successfully implemented in the Hongqihegou rail station, and the monitoring results show that the surrounding rock was adequately controlled throughout the excavation process.