Research on Deformation Laws of Deeply Buried Tunnels with Small Clearance in Soft Rock by Different Tunnelling Methods

To explore the mutual disturbance effect due to tunnelling of deeply buried the left and right tunnels with small clearance in soft rock, based on tunnel 1 of Dongmachang in Huali High-Speed Project, through field measured data analysis and numerical simulations, the deformation laws of tunnels with small clearance by dififerenent tunnelling methods for the and left and right tunnels in different clearances between working faces in deeply soft rock were studied. The results indicated that there was mutual disturbance between the left and right tunnels during tunnelling and the horizontal convergent deformation of the tunnel first was obviously larger than that of the tunnel later. The tunnelling method had a great influence on the deformation of tunnels, and the deformation by the three-step tunnelling for both double tunnels was 13% less than that by the two-step tunnelling. The deformation by the three-step tunnelling for the tunnel first and the two-step tunnelling for the tunnel later decreased by 12% than that by the three-step tunnelling for both tunnels, which was similar to that by the three-step tunnelling for both tunnels. The clearance between the left and right tunnels had a little influence on the settlement of the vault, but had a great influence on the horizontal convergence deformation of tunnels. With the increase of the clearance between working faces of the left and right tunnels, the time for deformation stability prolonged, the horizontal displacement gradually decreased, and the deformation decreased slowly when the clearance was up to 50 m. Comprehensively considering the construction period, construction cost and tunnel deformation control effect, the scheme for the tunnel first by the three-step tunnelling and the tunnel later by two-step tunnelling was suggested to tunnels with small clearance in deeply soft rock.If the clearance between working faces could be controlled beyond 50 m,the mutual disturbance between the both tunnels would be reduced.