Influence Of Shield Excavation On Adjacent Pile Foundation And Ground Settlement

In this study,taken the project of shield tunnel under-cross Wulidun flyover that a part of Hefei metro line 2 as engineering background,a three-dimensional numerical model was established via FLAC 3D.For typical geology in hefei,discussed the influence of ground settlement and adjacent piles which caused by shield tunnel construction.The following conclusions could be drawn from this research.The zone of formation subsidence or uplift in a transverse section spread like a cone from tunnel to the top and the bottom of model,but its value was attenuated continuously as the distance between piles and tunnel increases.The distribution of the surface settlements wasn’t similar to the curve invented by Peck.The difference of surface settlements in the area of contact surface was obvious,so its controlling essentials for surface stabilization.The horizontal displacement curves of the pile groups like a bow.In the middle-upper area,the horizontal displacement was bigger than other part.The transverse deformation of farther piles is more obvious than more resent ones when the distance between these piles and tunnel was close enough.In addition,The larger bending moment occurred at the top of the piles.When L = D(L was the distance from pile to tunnel and D was the diameters of the tunnel),the largest pile lateral(perpendicular to the respect to direction of shield advancing)displacement appeared at the middle part,the pile subsided obviously.And with the increase of L,the pile settlement decreased with a increased rapid.When L ≥ 1.5 D,the largest pile lateral displacement appeared at the top of the pile,when L wasn’t exceeding 3 D,these piles had a approximately same largest lateral value.If L increased and surpassed to 3 D,the largest value promptly decreased.When L ≤ 2.5 D,The lateral horizontal displacement curves of the pile like a bow and then the pile has a large bending moment.In addition,due to the large axial stiffness of pile shaft,the vertical displacement of pile foundation kept stable.As the value of L / D increased,the lateral horizontal displacement of pile top increased at first and then decreased.When the value of L / D was between 2 and 2.5,it achieved peak value.In the future engineering practice,the Peck original formula should be modified according to the experimental simulation of the current soil.In normal conditions,the effects beyond the 5 D range can be ignored.In order to control the surface subsidence well,the segments,grouting and secondary grouting should be carried outin time.In necessary,you can increase the grouting pressure properly.In addition,some reinforcement measures can be applied to the piles in the upper part to improve its power to resist bending deformation before the shield excavation.