Abstract:

The overburden of D2 access tunnel of Gulou Station of Nanjing Metro is only 1.3～1.6m. Above the access tunnel, there exist power cables and water supply pipes. Regarding the construction of the tunnel, comparisons are made between open cut method and undercutting method with shallow overburden and the latter is determined to be adopted. The paper presents the structural design and calculations of the access tunnel, as well as the construction method and the fundamental technical measures taken. The construction of the access tunnel has already been successfully completed, with the traffics on Zhongyang road having not been interfered and the ground surface settlement, structural deformation, construction schedule and waterproofing of the tunnel having met the relevant requirements. The successful experience of the access tunnel has already been used in the construction of the access tunnels of other Metro stations.

Key words: undercutting under supershallow overburden  , rectangular tunnel  , temporary support