The Surface Subsidence And The Influence On Piles Group Due To Urban Shallow Tunnels

With the booming development of the urban tunnel project in our country, many technical problems of tunnel engineering have been emerging. The surface subsidence caused by the shallow tunnel construction can bring many problems to urban environment, meanwhile the deformation of surrounding rocks may affect neighboring buildings’ foundation such as group of piles. So it has the important practical significance to forecast the surface subsidence, to analyze the distribution law of surface subsidence and to research the influences on the piles from excavation. Founded by the excavation engineering section in No.5line of Guangzhou metro, the paper used the methods of theory analysis, numerical simulation and project measurement to research the prediction of surface subsidence, the selection of tunnel construction methods and the influences on pile group from excavation. This paper’s main contents includes the following aspects:Using the theory of random medium where calculation process was simplified and the parameters in need was inverted, the paper concluded the surface subsidence caused by the construction of tunnel which goes through the surface buildings. In the end the rationality of the method was presented through the concrete example.Relying on underground tunnel of Guangzhou metro line NO.5, the mechanics calculation model of A4type cross section and G type cross section was established, through the investigation of surrounding rock stress, displacement of surrounding, rock mass, and internal forces of supporting structure and, the optimal construction schemes of the two tunnels were determined.Based on the optimal construction schemes of two different tunnels, by the numerical simulation method, the change of the surface subsidence analysis accompanied with the excavation steps and the process of excavation face was analyzed, the horizontal regularity of the surface subsidence and the longitudinal of regularity of the surface subsidence were obtained. In the end the calculated results were compared with the monitoring data.Relying on underground tunnel of Guangzhou metro line NO.5, where the tunnel of A4section nearly meet piles group of overpass, by the method of numerical simulation, the influence on piles group from the construction of shallow buried tunnel was studied, the axial force of pile body, the friction resistance of pile side the relative settlement between piles and soil and the settlement of pile caps before and after the excavation were obtained.