Model Test And Numerical Simulation Of Single Row Cantilever Inclined Long Short Composite Pile In Foundation Pit Excavation

The single row piles of cantilever pile support in foundation pit engineering are inclined to a certain angle,and the inclined piles are obtained,which can not only improve the ability of bearing horizontal load,but also restrain the deformation of pile body and the lateral displacement of support structure.In addition,the bending moment of the part below the excavation surface and away from the bottom of the pile is small.If the piles are arranged according to the same pile length,the material is often wasted and the potential of the supporting structure is not fully exploited.In this paper,the construction method of inclined pile,field test and indoor model test,vertical and horizontal bearing characteristics and other aspects of the research status are investigated.Based on this,the inclined long short composite pile is designed by combining the characteristics of inclined pile and long short pile,and its working behavior and supporting capacity are studied.It includes the following aspects:(1)Based on the support form of inclined long short composite piles,the working conditions of one long short and one long two short inclined composite piles are designed,and then the specific test scheme is formulated,and the test similarity ratio is determined by the approximate differential equation of deflection curve of beam in mechanics of materials.The inclination angles of the inclined piles are controlled as 0 °,10 ° and 20 ° respectively;the straight piles are always vertical due to the relatively short pile length.The data of lateral displacement of crown beam,ground settlement and bending moment of pile body of one long one short,one long two short and equal length straight pile are collected.(1)With the increase of inclination angle,the supporting capacity is enhanced,the ultimate excavation depth of foundation pit is improved,the performance of supporting structure is greatly improved,and the anti overturning ability is enhanced;(2)When the inclination angle increases,the maximum bending moment of the pile body decreases.The maximum bending moment of the inclined pile and the straight pile decreases slightly above the excavation surface,but more below the excavation surface.(3)For equal length straight piles,reducing the amount of piles will increase the bending moment near the excavation face;for long and short piles,increasing the proportion of short piles will make the long pile and short pile bear greater bending moment above and below the excavation face;when equal length piles are set as long and short piles,the maximum bending moment of long pile and short pile will increase above the excavation face,while under the excavation face,the maximum bending moment of long pile and short pile will increase The maximum bending moment of the pile increases and that of the short pile decreases.(4)The inclined long short composite pile can be regarded as a rigid frame under horizontal force.The inclined pile is equivalent to the slope treatment of the foundation pit,which helps to control the soil deformation.The component of its axial force in the horizontal direction not only limits the deep horizontal displacement of the pile,but also increases the pile side friction,so as to better control the soil deformation.(2)Based on the model test,the influence of changing the total length of inclined pile and straight pile on the supporting effect is further studied by numerical method.Under the condition of keeping the inclination angle of 10 ° and 20 °,the working conditions are designed as follows: the length of inclined pile is greater than that of straight pile;the length of inclined pile is equal to that of straight pile.The results show that:(1)When the total pile length and inclination angle are the same,the inclined long short composite pile is obviously better than the equal length inclined composite pile in controlling the deformation of soil and supporting structure.(2)When the total pile length is fixed and the straight pile meets a certain embedded depth,the inclination angle has a critical value.When the inclination angle is less than the critical value,the optimal distribution of pile length is affected by the inclination angle.When the inclination angle is greater than the critical value,the longer the inclined pile,the better the supporting effect.(3)The bending moment of inclined long short composite pile is different from that of equal length inclined composite pile.(3)Based on the actual foundation pit engineering and the field monitoring results,the 3D model of the original support form and the inclined long short composite pile support form is established by numerical means,and the comparative analysis is carried out.The results show that: For this project,the total length of the inclined long composite pile is smaller than the original support form,but its supporting effect is not less than that of the original pile anchor support.