Analysis Of The Effection For Shield Construction Beneath The Existing Overpass Bridge’s Pile Foundation

Based on the shield tunnel of Hefei Metro Line 2 shield through the Wulidun overpass pile group,the finite difference software FLAC^3Dwas used to establish the three-dimensional numerical model to analyze the law of the deformation of pile foundation and surface settlement caused by variation of the lagging distance of the face about the double-line tunnel and the pile’s load.And combined with theoretical analysis and field monitoring data for comparative analysis,the research work and conclusions are as follows:（1）Domestic and foreign scholars on the shield tunnel through the building（structure）of the relevant research methods and content were analyzed,as well as the safe construction of the project control measures were guaranteed.Then the influence factors of pile foundation deformation and surface settlement during shield through the bridge pile were summarized.The mechanism and regularity of surface settlement and pile foundation deformation caused by tunnel excavation were analyzed.（2）For the field monitoring data analysis can be seen:when the center distance of the double-line tunnel was constant,the cross section of the surface settlement trough caused by the tunnel excavation was similar to the shape of"W".The surface settlement above the right line tunnel was larger and the maximum settlement center point was shifted to the left.（3）When the center distance of the double-line tunnel was 3D（D was the tunnel diameter）,with the increase of the lagging distance of the face,the vertical settlement of the pile foundation between the two tunnels was gradually reduced,and the horizontal displacement was increased in an appropriate amount and the overall range was within 0³mm,and the center settlement of the right line tunnel was 6%to 17%larger than that of the left line tunnel.When the lagging distance was greater than or equal to 6D,the vertical settlement of the pile foundation between the double-line shield tunnel can be minimized.（4）With the pile load was increased,the horizontal displacement of pile foundation was not affected,the vertical settlement was increased,and the construction of the rear tunnel had a great influence on the deformation of pile foundation between the two tunnels.The influence of the pile foundation on the surrounding surface subsidence was approximately 1.5D radius within the center of the pile.When the pile load was less than or equal to the ultimate bearing capacity of the pile,it can effectively control the vertical settlement of pile foundation within the range of warning values to ensure the normal use of bridge structure.（5）When the center distance of the double-line tunnel was 3D,the longitudinal settlement of the top surface of the surface was similar to the stacked of two Peck fitting curves.After the double-line tunnel was excavated,the top of advanced shield above the surface settlement was greater than the hind shield.The maximum settlement of the surface was located at about 0.25D on the right side of the pile between the two tunnels and near the side of advanced shield.