Study On The Impact Of Tunneling On The Behaviors Of Adjacent Existing Piles

There is a great impact on adjacent pile foundation due to the excess ground movements by tunneling, which will disserve the safety of adjacent buildings. The study on the influence of tunneling to the behaviors of adjacent piles is very important for the safety of adjacent buildings, and it is an urgent problem for developing city subway tunnels cosmically. The study on this problem becomes more and more instant for that the actual impact of tunneling on adjacent piles is not very understood in domestic.The numerical tests are used to study the influence of excavation to piles through the software Plaxis 3D Tunnel, which is validated that its result is reliable via the comparison with the result of centrifuge experiment. The effect induced by tunneling in soft soil region on ground settlement and behaviors of adjacent single pile is studied under different influencing factors. The impact on lateral pile group is also studied, and the result is compared with the single pile at the same position. Finally, several constructive measures for reducing or eliminating the adverse effects on adjacent piles by tunneling are suggested. The conclusions of the numerical test are as follows:(1) When the excavated section propels a distance from half tunnel diameter to pile, the change of the ground settlement, deformation and stress of the adjacent single pile is the most acute.(2) When the pile lies at the side of the tunnel, and the pile toe exceeds the depth of the tunnel invert, the lateral influence zone induced by excavation is inside the distance that one and a half tunnel diameter from the out tunnel contour, and that the minimum safe distance between the out tunnel contour and the adjacent single pile is half tunnel diameter.(3) When the tunnel traverses the up piles, the lateral influence zone caused by tunneling is inside the distance that one tunnel diameter from tunnel centerline.(4) When the single pile just exists at the upside of the tunnel crown, the minimum safe distance between pile toe and tunnel crown is half tunnel diameter.(5) The distribution of horizontal displacement, bending moment and axial force of piles in the same row is almost being superposed.(6) The maximum bending moment of piles in the front row of the pile group is as much as the single pile, and the maximum bending moment of piles in the rear row is larger than the single pile slightly, furthermore the maximum axial force of piles both in the front and rear row is larger than the single pile at the same position.