Abstract: To avoid arch large deformation and ground collapse when tunneling through fracture zones, an excavation support system of the prestressed anchor bolt and bench method is designed for tunnels crossing fracture zones. The system is numerically modeled and compared with the hollow grouting anchor bolt and the central diaphragm (CD) method, and field tests are performed. The results reveal the following: (1) The prestressed anchor bolt and bench method have an excellent control effect on the surrounding rock deformation; simulation results show that the controlling effect of crown settlement, horizontal displacement, and excavation disturbance range of the surrounding rock in the recommended methods is superior. After arch penetration, the final surrounding rock deformations using the bench method and the CD method are stable at 6.8 mm and 11.5 mm, respectively. (2) The active support site monitoring results indicate that the settlement of the crown is mainly concentrated during the excavation of guide hole No. 1, and the evolution process can be divided into acceleration, development, and stability stages. (3) The grating steel frame′s stress is primarily compressive, with the crown stress exceeding 90 MPa; the axial force of the anchor bolt evolves through three stages with tunnel excavation: prestress loss, fluctuation, and stability, with the change not exceeding 0.1 kN/d after stabilization.

Key words: tunnel engineering, soft and weak fracture zone, active support, bench excavation method, central diaphragm method, field test