ENGINEERING GEOLOGICAL MECHANISM ON DEFORMATION OF NANJING METRO TUNNEL IN OPERATING

This paper is based on the engineering geological and hydrogeological conditions of Nanjing and the long-term monitoring data on the deformation of structures. The tunnel deformation characteristics in various geomorphic units are analyzed systematically. The effects of soft soil on shield tunnels and the hydrogeological conditions on mining tunnels are determined as the major engineering geological factors dominating the deformation of Nanjing metro tunnel. There are various kinds of soft soils in Nanjing. They are formed in different sedimentary conditions. Those soft soils, typically those in the valley plain area of Yangtze River, are of high void ratio, great water content, high compressibility and sensitive structure. These properties can easily lead to uneven settlements of the shield tunnels. As to the mining tunnels through the hilly area, the lining structure can be uplifted by the groundwater gradually when the groundwater exceeds the normal water table. As a result, the operation of metro tunnels can be disrupted seriously. This study fosters the understanding of the deformation of metro tunnels from the engineering geological perspective, and offers a theoretical basis to monitor and control the deformation and ensuring the safety of the tunnels in operating.