Optimization Research On Deformation Control Scheme Of Double Row Pile Foundation Pit Support

The urban infrastructure are becoming more and more intensive,and there are more and more deep foundation pit projects.The double-row pile foundation pit support has also been paid more and more attention.Therefore,it is of great engineering significance to carry out the optimization of the double-row pile foundation pit support design and its influence on the settlement of the surrounding existing building foundation.In this paper,a three-dimensional finite element foundation model is established based on the engineering case of double-row pile support for foundation pit in loess stratum.The influence of the construction sequence,pile spacing,row spacing,pile diameter,pile length and excavation depth of double-row piles on the lateral deformation and stability of foundation pit and the settlement of surrounding existing building foundation is analyzed and optimized.The following conclusions are obtained :(1)When the excavation depth of the foundation pit is less than 12 m,the maximum settlement of the loess foundation of the existing building is far away from the foundation pit.When the excavation depth is greater than 12 m,the maximum settlement of the loess foundation of the existing building is close to the foundation pit;the lateral displacement of double-row piles increases with the excavation depth of foundation pit,while the anti-inclination stability,embedded stability and overall stability of foundation pit decrease with the increase of excavation depth.(2)When the pile length of the front and rear piles is set to be equal,the design of the doublerow pile length should be greater than or equal to 1.6 times the total depth of the foundation pit;when the pile length of the front and rear piles of the double-row pile supporting structure is not equal,the pile length of the front pile should be the same as that of the equal length scheme,and the pile length of the rear pile should be greater than the excavation depth of the foundation pit.The change of the pile length of the front and rear piles makes the lateral displacement and embedded stability of the double-row piles less affected,while the overall stability of the foundation pit increases.(3)The variation of the settlement range of the existing building loess foundation is consistent with that of the row spacing of the double-row pile supporting structure.The larger the row spacing is,the stronger the lateral deformation of the foundation pit and the settlement control of the existing building loess foundation are.The optimal row spacing of double-row piles is 4～6d(d is pile diameter);the anti-inclination stability,embedded stability and overall stability of foundation pit of double-row piles increase with the increase of row spacing.(4)The pile diameter of double-row piles has great influence on the uneven settlement of loess foundation of surrounding existing buildings.The optimal pile diameter range of doublerow piles supporting structure is 0.8 ～1.0 m,and the optimal pile spacing is 2 ～3 d;the anti-dip stability and embedded stability of double-row piles increase with the increase of pile diameter,while the pile diameter has little effect on the overall stability of foundation pit.The anti-dip stability of double-row piles decreases with the increase of pile spacing,while the pile spacing has little effect on the overall stability of foundation pit and the embedded stability of doublerow piles.(5)The construction sequence of the front and back row piles has no effect on the lateral deformation of the foundation pit,the overall stability of the foundation pit,the embedded stability of the double-row piles,the anti-dip stability and the settlement of the loess foundation.(6)On the premise of ensuring the stability of foundation pit,the relationship between foundation settlement and time obtained by different settlement models is compared and analyzed.Among them,the correlation coefficient between the calculated value of the composite powerindex(CPE)model and the measured value of the foundation settlement is 0.97,which is highly consistent.The final settlement of any point of the foundation can be predicted.The settlement prediction of multiple points can realize the prediction of the uneven settlement of the surrounding existing buildings.