| The subway is an important means for us to go out.The foundation pit of subway station is usually deep and large foundation pit,and open excavation method is often used in construction.Therefore,it is often difficult to resist the invasion of heavy rainfall during construction,resulting in the instability and deformation of foundation pit soil and support structure.Previously,people spent a lot of time studying the slope under heavy rainfall before,but less on the impact of heavy rainfall on the foundation pit.Therefore,it is necessary to study the stability of loess deep foundation pit under heavy rainfall.Taking the main deep foundation pit project of Changming Road Station of Xi’an Metro Line 8 as the research object,this paper carries out the following work: firstly,the rainfall infiltration theoretical model in loess area is summarized,and then the one-dimensional vertical infiltration test of soil column is carried out according to the ponding infiltration theory to explore the infiltration depth of soil column under different ponding thickness and the attenuation of soil mechanical properties within the infiltration range.Then analyze the measured data of the foundation pit after encountering heavy rainfall weather during the construction of deep foundation pit,and explore the specific impact of heavy rainfall on the foundation pit.Finally,use Midas finite element software to model the actual foundation pit.Firstly,compare and verify the reliability of the model,then analyze the impact of heavy rainfall weather on the foundation pit support structure,and then simulate eight different heavy rainfall conditions,The influence of different rainfall duration and heavy rainfall conditions on the foundation pit is analyzed respectively.Finally,the overall stability coefficient of the foundation pit under different heavy rainfall conditions is analyzed and calculated,the support structure parameters of deep foundation pit under heavy rainfall conditions are optimized,and the construction scheme of foundation pit under heavy rainfall weather is put forward.After summing up,the author of this paper mainly comes to the following views:（1）According to the one-dimensional vertical infiltration test of soil column,the migration rate of wetting peak will decrease with the increase of infiltration depth.The shear strength of loess has been attenuated to a certain extent under the action of ponding infiltration.Ponding infiltration mainly affects the surface soil.The cohesion of loess has decreased significantly,with a maximum decrease of 68.2%,and the effective reduction range is about 1 / 2 of the infiltration depth.（2）Heavy rainfall will increase the overall horizontal displacement of the pile and offset to the pit.The influence of heavy rainfall on foundation pit is mainly reflected in three aspects:surface settlement,support pile displacement and pile bending moment,and increases in varying degrees under the influence of heavy rainfall,among which the increase of support pile displacement is the largest,The maximum offset occurs at 3 / 5 times the length of the pile shaft.（3）The duration of rainfall is the key conditions for shaking the stability of foundation pit.The overall stability coefficient of foundation pit decreases by 8.36% with the increase of rainfall duration.The rainfall weather with low intensity but long duration will have a Significant damage to foundation pit.Deepening the embedded depth of the retaining pile can effectively resist the adverse effects of some heavy rainfall,reducing the horizontal spacing of the first concrete support can effectively reduce the excessive surface settlement caused by heavy rainfall,and reducing the horizontal spacing of the fourth steel support can effectively resist the excessive deviation of the pile body to the pit;Some difficulties in foundation pit operation,it is most suitable to control the initial moisture content of loess in the foundation pit at 16%. |
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