To solving the engineering problems of tunneling in backfill soils, the shallow buried concealed excavation of the northern line of the Zengjiayan Bridge Tunnel Project in Chongqing has been taken as the relying project and numerical analysis and monitoring have been used to study on deformation characteristics of surrounding rock in small clearance tunnel excavation in backfill soil layer. The result of this study reveals that: firstly, during the excavation the maximum surface settlement will move from the top of the advance tunnel to the top of the intermediate rock pillar. Secondly, the surrounding rock deformation pattern of the backward tunnel could be described as: predeformation-sharp deformation- deformation convergence, and the surrounding rock deformation pattern of the advance tunnel could be described as: predeformation-sharp deformation- first deformation convergence- additional deformation- final deformation convergence. Thirdly, the excavation of the advance tunnel will lead to the predeformation in vault, arch and the side wall of the backward tunnel, and the excavation of the backward tunnel will lead to the additional deformation in the same places of the advance tunnel. The conclusion of this study is consistent with the existing research and can provide reference for similar projects.

Shaoguan was hit by a extremely heavy rainstorm, and the mountain watercatchment of Dabaoshan Tunnel in the southern of Beijing HongKong Macao Expressway in Guangdong increased sharply. Due to therapid rise of groundwater level, water and mud gushed at ZK141+227 ofDabaoshan, and serious water seepage occurred in other areas, bringing soilinto the tunnel, which seriously hindered the safe passage of the tunnel.According to the on-site investigation of water and mud gushing, it wasfound that there were branches sandwiched in the mud gushing out, andat the same time, it was found that there was water leakage at the foot ofsome walls where drainage holes were added. Based on the fluid structurecoupling mechanism, the seepage mechanism of highway tunnels was deeplyexplored, and the mechanical properties of tunnels under seepage were ana-lyzed through experimental data and numerical simulation. The experimentalresults show that under the action of seepage, the stress distribution of the tunnel lining changes, and the phenomenon of local stress concentration isobvious. When the seepage pressure reaches 3.5 MPa, cracks appear in thetunnel lining, with a total of 5 cracks. The distribution of cracks is closelyrelated to the seepage field. The numerical simulation further reveals theinteraction mechanism between the seepage field and the tunnel structure,confirming the influence of the seepage field on the stability of the tunnellining. When the seepage pressure increases to 4.0 MPa, the displacementchange rate of the tunnel lining reaches 0.3 mm/m, and the maximum liningstress is 15.7 MPa. The purpose of this study is to propose a maintenance planfor highway tunnels to improve their safety. Consider the impact of seepageon tunnel structure and adopt effective waterproofing and drainage design.Further research on the seepage mechanism and tunnel mechanical propertiesis recommended to provide more reliable theoretical support for engineeringapplications.