Research On Deformation Caused By Excavation Of Ultra-deep Foundation Pits In Semi-diagenetic Stratum

With the continuous development of China's underground space engineering,the foundation pit project gradually shows the characteristics of "large,deep,tight and adjacent".The continuous emergence of these super-large and ultra-deep foundation pits has gradually increased the difficulty of their construction,inevitably affecting the surrounding environment.If the deformation of the foundation pit is not strictly controlled,it may cause a series of problems such as instability of the foundation pit and cracking of surrounding buildings.Therefore,it is particularly important to analyze the deformation of these complex subway deep foundation pits.?This article takes the ultra-deep wind pavilion foundation pit of Qingxiushan Station of Nanning Rail Transit Line 3 as the background.based on the previous research results,the detailed analysis of the site monitoring results is carried out,and the ultra-deep wind pavilion foundation pit is three-dimensionally analyzed.The numerical simulation analyzes the deformation of the enclosure structure,the surrounding ground surface,the supporting axial force,and the deformation laws of the surrounding buildings.The main tasks completed in this article are:(1)The field survey data of the excavation of the ultra-deep foundation pit is analyzed in detail.Investigate the deformation law of the enclosure structure during the excavation of the ultra-deep foundation pit,the settlement law of the ground surface,the change law of the supporting axial force,and the deformation law of surrounding buildings,and analyze the reasons for it.?(2)The MIDAS/GTS finite element software was used to carry out three-dimensional modeling and analysis of the ultra-deep foundation pit.The constitutive model was selected to modify the Mohr-Cullen model,and the ultra-deep foundation pit was excavated layer by layer and reinforced layer by layer.The effects of foundation pit excavation on the enclosure structure,surrounding soil,supporting axial forces,and surrounding buildings were calculated.The numerical simulation calculation results are compared with the on-site monitoring results.The deformation of the two is basically the same,which indicates that the parameters selected by the model are reasonable,and it has certain reference significance for similar projects in the future.(3)The parameter sensitivity analysis of the supporting structure of the foundation pit was carried out,and the depth,width and supporting rigidity of the supporting structure were changed for three-dimensional numerical simulation,and its effects on the enclosure structure,surrounding soil,supporting axial force,and the deformation of surrounding buildings were discussed.It is concluded that the width of the supporting structure has the largest influence on the excavation deformation results of the foundation pit,the second is the effect of the support stiffness,and the smallest influence of the depth of the supporting structure.(4)The deformation rules of this ultra-deep foundation pit are compared with other deep foundation pits.It is concluded that the deformation of the enclosure structure of the ultra-deep foundation pit,the surrounding soil,and the maximum deformation position are basically consistent with the deformation laws of other foundation pits.But its maximum deformation is small.