| In recent years,China’s urbanization construction has continued to develop,people’s exploitation of urban space resources has become more and more effective,and deep foundation pit engineering has become a key step in urban high-rise buildings,rail transportation,large municipal facilities and other projects,and is increasingly widely used.However,the increasingly complex surrounding environment,strict requirements for foundation pit deformation and high construction safety requirements are major challenges for deep foundation pit in the future.The stability of foundation pit is affected by many factors.At present,most of the research results are to analyze the influence of each factor on the stability of foundation pit separately,and there is a lack of research on the deformation and stress variation of foundation pit under the condition of multi-factor adjustment.In this paper,by summarizing the deformation mechanism of foundation pit and related research results,taking the actual project as an example,the stability of foundation pit is discussed and analyzed by means of finite element numerical analysis,orthogonal experiment and field monitoring.Firstly,through the establishment of three-dimensional numerical model,according to the field monitoring results and numerical calculation results,the excavation deformation law of foundation pit is summarized and explored to verify the reliability of the three-dimensional model.Secondly,the variable scheme of influencing factors is formulated,and three groups of indicators are selected,including the maximum uplift of pit bottom,the maximum horizontal displacement of enclosure structure and the maximum surface settlement outside the pit.The control variable method was used to analyze the deformation law of foundation pit under different adjustment conditions.Furthermore,the orthogonal test method was used to comprehensively analyze the influence of various factors on the stability of foundation pit under the coupling effect,and the importance was sorted according to the influence degree.Finally,the foundation pit support scheme was optimized based on the numerical simulation results.The specific research contents are as follows:（1）Using the finite element software to foundation pit excavation process in numerical simulation of the deformation and stress change rule of horizontal displacement of retaining structures was determined as the "complex",the maximum value is 17.72 mm,the distance of pile top 13.08 m;The surface settlement outside the pit presents a "concave pit shape".The maximum settlement is 0.55H（H is the excavation depth）from the edge of the pit,and the maximum value is 11.72 mm.The first internal support is subjected to pressure,and then the pressure gradually increases but decreases.（2）Analysis of field monitoring data,the numerical simulation results in the extraction and monitoring the same location data contrast analysis,the results show that the numerical simulation calculation and monitoring data of basically the same trend but local differences,and puts forward the cause of the differences,verify the three-dimensional simulation has a certain reference.（3）Formulation variables influencing factors of deep foundation pits,modulus of soil,soil cohesive force,the brace stiffness,retaining pile diameter and spacing of five factors,based on the control variable method in foundation pit uplifts of quantity outside the surface subsidence,horizontal displacement,pit maximum as evaluation index,40 groups of simulation test design,aims to explore the influence factors in the foundation pit deformation law under the conditions of different adjustment.The results show that the deformation of foundation pit can be effectively restrained by other factors except the spacing of retaining piles.The influence of soil modulus on foundation pit stability is obvious,while the influence of retaining pile spacing on foundation pit stability is weak.At the same time,with the increase of the change degree of each influencing factor,its constraint effect has an obvious upper limit.（4）According to the example project,optimize the variable range of influencing factors,establish the orthogonal test table of five factors and four levels,compare and explore the calculation results of orthogonal test by range analysis and analysis of variance,and comprehensively analyze the influence on the stability of foundation pit under the coupling of various influencing factors.With comprehensive reference to the calculation results of various assessment indicators,the influencing factors are sorted according to the degree of influence as follows: soil modulus,soil cohesion,internal support stiffness,pile diameter and spacing of retaining piles.（5）According to the calculation results of orthogonal test under each assessment index,combined with the actual situation of the project and based on economic benefits and other factors,the original support design is optimized.Finally,the optimal combination is determined as follows: the pile diameter of retaining pile is 0.6m,the spacing of retaining pile is 1.1m,and the horizontal coefficient of internal support stiffness is 1.2 times.According to the selection of assessment indicators and the comparison of the numerical simulation results before and after optimization,it can be concluded that the deformation of the foundation pit after optimization is significantly reduced,in which the uplift of the pit bottom,the horizontal displacement of the retaining structure and the surface settlement outside the pit are reduced by 15.3%,19.8% and 24.5% respectively,and the optimized design scheme appropriately reduces the pile diameter of the retaining pile and improves the spacing of the retaining pile,so as to improve the economic benefit.Figure [70] Table [21] Reference [65]... |
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