Research On The Influence Of Ground Deformation Due To Excavation And Dewatering Of Deep Foundation Pit In Semi-diagenetic Stratum

In recent years,with the continuous development of urban underground space and the vigorous development of rail transit construction,the construction of deep foundation pits for subway stations is also increasing.The deformation problem of deep foundation pit under the joint action of excavation and precipitation has become an important research content in subway construction.Based on the deep foundation pit of Qingxiushan Station of Nanning Metro Line 3,this paper proposes a reasonable construction plan based on the semi-diagenetic stratum environment and excavation characteristics of the deep foundation pit,and establishes a three-dimensional finite element calculation model,which is comprehensively and meticulously analyzed.The factors affecting the deep foundation pit and surrounding environment under the conditions of precipitation and the changing laws,the main research results are as follows:(1)The deep foundation pit of Fengting Formation is the ultra-deep excavation of semi-diagenetic strata.The support scheme adopts the form of bored pile and 12 inner support.The precipitation scheme adopts the method of pipeline well precipitation,and the excavation scheme adopts the reverse method.And Construction method by combining the methods.(2)The 3D model of the deep foundation pit of Fengting Formation was established by MIDAS GTS/NX finite element software,and the causes of the change of seepage field caused by precipitation work were analyzed.The stepwise precipitation in deep foundation pit engineering was simulated according to the actual working conditions.Through the whole process of excavation and one-time precipitation excavation,the deformation law and influence of deep foundation pit construction,such as ground settlement,deformation of retaining structure,foundation bulge and internal support axial force,are analyzed.The precipitation excavation method found that the step-by-step precipitation excavation construction method is safer and more reasonable;comparing the simulation results with the actual monitoring data,the values of the two are very close,and the deformation law is basically consistent,so the numerical simulation results have reference to the actual project.Sexual value.(3)Under the construction method of step-by-step precipitation excavation,the depth and width of the retaining structure are changed,and the influence degree and variation trend of the four factors of the depth and diameter of the column on the deformation of the deep foundation pit are simulated.Although the change of width and width has an impact on the surface settlement and deformation of the retaining structure,it will seriously increase the construction cost.Therefore,other effective measures are recommended under the premise of ensuring the safety of the deep foundation pit;the depth and diameter of the column change to the surface settlement and The deformation of the retaining structure has little effect,but the column plays a key role in the support system of the deep foundation pit,which largely determines the stability of the deep foundation pit.Therefore,it is still necessary to select the column size that is both economical and applicable under the premise of meeting the rigidity requirements of the column itself.Choosing the optimal construction plan can achieve resource conservation and reduce construction costs.