Field Measurements and Numerical Analyses of Double-Layer Pipe Roof Reinforcement in a Shallow Multiarch Tunnel

The longitudinal deformations of the pipe roof in the entrance of a shallow multiarch tunnel of Tujiangchong were monitored by a series of strain gauges, and the working mechanism of the pipe roof was analyzed according to the field test results. A three-dimensional finite difference code, FLAC^3D, was adopted to simulate the deformation of the pipe roof and to evaluate its effect on ground surface settlement. Both the calculated and numerical results fit the field observations quite well. The numerical results indicated that a double-layer pipe roof provided a restraining effect on ground movement and helped to reduce the tunnel deformation and corresponding ground surface settlement. Ground settlement directly above the crown could be reduced by 40% to 50% compared with the settlement induced by tunneling without any pipe roof reinforcement. This project provided a successful case history of using double-layer pipe roof reinforcement in a shallow multiarch tunnel construction.