Study On The Influence Of Cantilever Supported Foundation Pit Excavation On Adjacent Double Pile Foundation

In the past,the research on the foundation pit engineering mainly focused on the stability of the foundation pit,the internal force and deformation of the supporting structure,and the drainage of the foundation pit.With the rapid development of urban construction,it is often found that there are built(structure)pile foundation around deep foundation pit in engineering practice.When these pile foundations are within the influence range of excavation,excavation and unloading of foundation pit will lead to different degrees of additional effects on adjacent pile foundation.The mechanical deformation characteristics of this pile foundation are different from those of engineering pile in pit,and its stress deformation mechanism is extremely different Complex.Therefore,relying on the applied basic research project of Yunnan Province(2017fb088),this paper has carried out in-depth and systematic research on the impact of foundation pit excavation on adjacent pile foundation.The main contents and conclusions are as follows(1)The scale model test of the influence of cantilever support foundation pit excavation on adjacent double pile foundation is carried out,and the variation rules of additional bending moment of pile foundation,horizontal displacement of pile body,rotation angle of pile cap,settlement of pile cap and horizontal displacement of supporting structure with excavation of foundation pit are discussed.The test results show that: the maximum bending moment of the front and rear piles is 1.06 and 1.43 times of the pile length of 0.5m;the horizontal displacement of the pile top is 0.24 times;the angle of the bearing platform is 1.4 times;the settlement of the bearing platform is 0.651 times;the horizontal displacement of the top of the supporting structure is 0.787 times.(2)Through the comparison of finite element numerical simulation and indoor model test,the simulation results are basically consistent with the test data,which verifies the rationality of the numerical simulation.On this basis,the numerical simulation research on four influencing factors,namely,soil cohesion,support stiffness,length depth ratio(pile length to excavation depth ratio),and pit pile distance(from the edge of foundation pit to the pile Center),is carried out.According to the results of this numerical simulation,it is concluded that:(1)When the cohesion increases within 8 kPa,the bending moment,horizontal displacement,settlement of pile cap and the angle of pile cap gradually decrease.When the cohesion exceeds 8 kPa,the decreasing trend is obviously slowed down.(2)With the increase of support stiffness,pile bending moment,pile horizontal displacement,pile cap settlement and bearing platform angle decrease.When the support stiffness exceeds 51.2 n · m~2,the change trend of pile bending moment and horizontal displacement is not obvious;when the support stiffness exceeds 100 N · m~2,the reduction of bearing platform settlement and angle is no longer obvious.(3)With the increase of length depth ratio,the bending moment of pile shaft increases.When the length depth ratio exceeds 1.8,the increasing trend is no longer obvious;the horizontal displacement of pile body decreases;the settlement of pile cap is the most significant;the settlement of pile cap with length depth ratio of 0.75 is 5.96 times of that of length depth ratio of 2.15;the angle of pile cap increases obviously,(4)With the increase of the distance between piles,the bending moment,the maximum horizontal displacement,the settlement and the rotation angle of the pile body decrease.The bending moment and horizontal displacement of the pile body have a great influence when the excavation depth is 2.5 times;when the pile cap settlement and rotation angle are within 2.0 times of the excavation depth,the influence is greater.(3)The response degree of additional internal force and additional deformation of pile foundation after setting isolation wall is studied through the measures of setting isolation wall in active area reinforcement soil,and the results are compared with those without isolation wall.The effect of isolation wall setting is analyzed by controlling different reinforcement depth,stiffness and plane position of isolation wall.The results show that: 1(1)The results show that the additional stress and deformation of pile foundation are much smaller than those without isolation wall.When the reinforcement length is 1.5 times of excavation depth,the reinforcement effect is the best when the reinforcement length is 1.5 times of excavation depth,and the reinforcement effect is the most obvious when the horizontal displacement of pile top and the settlement of pile cap are 1.25 times of excavation depth Reason.(2)Through the analysis of the simulation results of two groups of different pile lengths,it is concluded that the increase of the reinforcement stiffness of the isolation wall has little effect on the additional bending moment of the pile body,which is beneficial to reduce the horizontal displacement of the pile body,the additional settlement of the pile cap and the angle of the pile cap.(3)The additional effect of pile foundation is largely affected by the plane position of the added solid.With the decrease of S1(distance between the wall and the pile),the maximum bending moment of pile shaft,horizontal displacement of pile top,maximum settlement of pile cap and maximum rotation angle of pile cap basically decrease.