Research On Influence Of Existing Pile Foundations On Surface Settlement Caused By Shield Tunnelling In Soft Soil Area

With the rapid development of underground rail transit in China,the shield tunneling method is widely used in the construction of subway tunnels.Although the construction of shield tunnel can better control the settlement of soil layer,it still inevitably disturbs the movement and deformation of surrounding soil caused by soil.If the construction management is not properly controlled,it will cause excessive disturbance to the soil layer,resulting in a large number of subsidences on the surface.Each city needs to establish a certain control limit on surface deformation in order to build a subway.Most of the studies on surface settlement caused by shield construction did not consider the existence of pile foundations.In this paper,the ground settlement caused by the construction of shield tunnels under the influence of existing pile foundations is systematically studied by using the actual measurement analysis method,numerical simulation method and formula derivation.The empirical formula of surface settlement caused by the construction of shield tunnels under the influence of existing pile foundations is proposed.The specific research contents and innovation work are as follows:1.The construction of shield tunneling in the interval of HangzhouMetro Line 2 was monitored,and the applicability of the empirical formula of surface settlement in Hangzhou area and the effect of ground pile settlement under the influence of pile foundation were studied through the consolidation and analysis of measured monitoring data.2.Study the effect of pile foundations with different pile diameters,pile spacings and different distances from the tunnel on the surface settlement caused by the construction of shield tunnels.Use the MIDAS finite element software to establish a shield tunneling model.Studying the law of ground settlement under the influence of pile foundation.Based on the experience formula of Peck surface settlement without the influence of piles,according to the obtained ground settlement characteristics under the influence of different pile diameter,pile spacing,pile foundation and tunnel distance.The empirical formula of ground settlement under the influence of pile foundation was deduced.3.When simulating the effect of different pile lengths on surface settlement caused by shield construction,it was found that different lengths of pile foundations have an effect of increasing or decreasing surface subsidence,that is,there exists a “sinking area” and a “adding area”.According to the summary law,the pile foundation and the tunnel are at different distances,and the pile foundation influences the demarcation point of “subsidence reduction” and “plus settlement” of ground surface settlement.Draw the dividing line between “sinking area”and “adding area”.4.Based on the demarcation line of “reducing effect” of pile foundation,the influence of different lengths of pile foundation on the settlement of ground surface at the boundary of “reduction effect” was explored.And under the conditions of the pile with or without load,the“reduction effect” of the boundary line changes.5.The influence of submerged pile foundations with different grouting positions and buried pile foundations with different positions on the subsidence of the subsidence reduction effect line was studied.