Analysis Of Row Piles Deformation And The Global Stability In Pile-anchor System Of Foundation Pit Under Local Load

With the acceleration of urbanization,the development of underground space is unprecedented,foundation pit support becomes an indispensable part,among which the underground retaining structure of pile-anchor retaining structure is common,which can be applied to many soil and has good deformation control performance.At present,the theoretical research and simulation analysis of pile-anchor retaining structure tend to mature,but the influence of surrounding environment is rarely studied,and further consideration is needed.This paper focuses on the local load around the foundation pit,and studies the stress,deformation,overall stability and the sensitivity of the relevant parameters to the deformation of the retaining structure under local load by improving the theoretical formula and numerical simulation analysis.Besides,the spacing between the retaining piles under the local load is optimized,and the stability safety factor is combined to obtain the limit value of local surcharge outside the pit.The details are as follows:(1)The working mechanism and deformation calculation method of pil e-anchor retaining structure for deep excavation are summarized,and the non-linear horizontal additional stress on the retaining structure under local load is analyzed to establish the deflection differential equation of the supporting pile.The finite di fference method is used to solve the internal force and displacement of the supporting pile.At the same time,the numerical simulation result of the engineering example is compared with the calculation result,which verifies the rationality of the improve d method.In addition,the soil arch behind the pile formed between the pile and the soil is analyzed,and it is clear that the soil arch formed by the supporting structure under local load needs to consider the simultaneous action of three principal stres ses,so the unified strength theory is selected as the failure criterion,the calculation method of reasonable pile spacing is obtained through geometric relations and strength conditions,and the engineering example data is substituted,and the applicabil ity of the calculation method is verified by combining the optimization result and the deformation control index of the supporting structure,which can provide a reference for the design of the supporting structure with similar characteristics in accordanc e with.(2)Based on the analysis method of overall stability of foundation pit,the stress characteristics of soil under local load are analyzed,and the influence of local load is transformed into the change of stress state of soil on sliding surface.Wi th the help of additional stress method and the dangerous sliding surface obtained by Lizheng software,the safety factor of overall stability is solved.Combining with the engineering example,the simulation verification is carried out,and the difference of the results is analyzed,which shows the feasibility of the improved method.Then,the characteristic value of the foundation bearing capacity is introduced through the relationship between the safety factor and the reduction factor.According to the relative position between characteristic value curve of foundation bearing capacity outside pit and local load intensity curve outside pit,the limit value of local surcharge outside pit is determined,which provides reference for the evaluation of foundati on pit supporting scheme.(3)Through the control variable method and numerical analysis software,the influence law of many parameters on the deformation of pile-anchor retaining structure is analyzed,and the influence law of three elements of local load,supporting pile diameter,pile spacing,anchor cable prestress and anchor cable incidence angle on the maximum horizontal displacement and pile top horizontal displacement of supporting structure is analyzed,and then the correlation degree of the seven parameters to the two deformation characteristic values of the retaining structure is calculated by the improved gray correlation method.The comprehensive analysis shows that the sensitivity of pile spacing and local load strength is high,while the sensitivity of anchor cable prestress and distance between local load and pit edge is low.