Study On Mechanical Performance Of Row Pile With Inner-brace Retaining Structure Of Deep Foundation Pit

The foundation pit project is greatly affected by the engineering and hydrogeological conditions and surrounding environment of the site.Row Pile with Inner-Brace Retaining Structure are widely used due to their advantages of high reliability,non-invasion of the red line and strong adaptability of the site.However,the law of the forces and deformations of the row piles and the settlement of the foundation pit soil are still not clear enough and need further study.Therefore,the study of the internal forces and deformation laws of piles during excavation,the settlement rules and influencing factors of soil,the determination of relevant design parameters of foundation pit and the prediction of the degree of influence of excavation on surrounding buildings and underground pipelines,has important theoretical and practical significance.In this paper,based on a foundation pit project in Jiamusi,the variation laws of internal force and deformation of supporting structure and the deformation laws of soil around foundation pit are studied.The main contents are as follows:(1)The domestic and foreign research status and research results of the internal force and deformation law of the retaining structure and the deformation law of foundation pit soil are briefly discussed.(2)Briefly summarized the deformation theory of foundation pit,soil pressure theory and the types and characteristics of common used foundation pit support forms.According to the actual engineering geological conditions,the standard design calculation theory was applied to calculate the foundation pit support,and the supporting scheme of this project was determined.(3)The numerical simulation software FLAC3 D was used to simulate the 3D analysis of the foundation pit.The deformation and internal forces of the piles and the variation of foundation soil displacement with foundation pit excavation were analyzed.It was found that with the increase of excavation depth,pile bending moment increased obviously.The position of the maximum bending moment decreases continuously with the excavation of the foundation pit,and the bending moment of the pile body is significantly concave at the erected support position,which indicates that the erection of the inner brace can effectively control the bending moment of the pile body.With the increase of the excavation depth,the lateral deformation of the pile occurred obviously,and the displacement increase and then decrease along the pile,just like an arch and the deformation increased continuously.The maximum deformation occurred in the lower part of the foundation pit close to the bottom of the pit.The deformation of the pile has obvious spatial effect.Along the side of the foundation pit,the displacement of the middle of the side is the largest,and the displacement to the corner of the foundation pit is reduced due to the pit angle effect.The excavation of the foundation pit causes the uplift of the soil body at the bottom of the foundation pit.The general trend is the maximum uplift is in the middle of the pit,the smaller of the uplift the more near to the edge of the foundation pit and the uplift amount tends to increase with the increase of excavation depth.(4)The influencing factors,such as changing the row pile diameter,row pile length,supporting position and so on,on the internal force and deformation of row piles and the settlement of soil around the foundation pit are analyzed by numerical simulation method.By adjusting the parameters,the effects of the above factors on the deformation of foundation pit are studied.It is found that increasing the pile diameter or length of the pile can reduce the deformation of the pile and the settlement of soil around the foundation pit.But when the pile diameter or pile length Increase to a certain extent,the effect of reducing the deformation of the pit decreases.By changing the position of the support also affect the deformation of the pit.Properly reduce the position of the support can avoid excessive settlement of the ground around the pit.When the project requirements are met,the effect of decreasing the deformation of foundation pit by increasing the pile diameter or pile length will continue to decrease.Decreasing the support position too much may cause the cantilever excavation status and lead to the increase of the displacement at the top of the row pile and the influence range of the soil horizontal displacement of foundation pit.