Abstract: In order to analyze the influence of adjacent overcrossing construction of a newlybuilt tunnel on existing tunnel, a 3D FEM model is established to simulate the large crosssection Hongyancun Highway Tunnel (HHT) crossing above the existing Rail Transit Loop Line Tunnel (RTLLT) in Chongqing with the minimum vertical clear spacing of 0.33 m. And the distribution and variation laws of stress and deformation of the secondary lining of RTLLT are obtained and analyzed. The results show that: (1) When the bench method is used for HHT, the influence of excavation of top heading and middle bench on the RTLLT is the largest, while that of the excavation of lower bench is the smallest. (2) The deformation of RTLLT is characterized by vertical deformation, and the maximum values locate at the four crossing sections of the RTLLT right below the HTT, where cracks might appear in the secondary linings due to the large tensile stress. In addition, the stress and deformation variation of RTLLT can be divided into three stages with the excavation of HHT, and the 58meterlong core excavation control region for HHT can be determined. Accordingly, the construction control area is divided and different construction methods such as controlled blasting with second delay detonators and mechanical excavation are used to ensure the successful overcrossing construction of HTT.

Key words: small clear spacing tunnels, adjacent tunnel, overcrossing construction, mechanical analysis, numerical simulation