Study On Retaining Structures For Large Deep Exavations In Deep Soft Soil Under Complex Environment

This thesis reviews the distribution and engineering characteristics of deep soft soil layer in Nansha area of Guangzhou.Based on the parameter characteristics of HSS model in soft soil and the results of laboratory soil test,combining the calculation of typical cases and the comparative analysis of field monitoring data,the relationship between the compression modulus of soft soil in Nansha area of Guangzhou and the four stiffness parameters of HSS constitutive is obtained.It lays a foundation for the calculation and analysis of HSS model in soft soil in Nansha area of Guangzhou.Secondly,the common selection of foundation pit support in Nansha area of Guangzhou is sorted out and through the typical geological section and its main influencing factors.Plaxis software and Lizheng deep foundation pit calculation software are used to compare and analyze the results.And a more reasonable parameter setting is obtained.Thirdly,through statistics of foundation pit deformation under different conditions,the rule of deep soft soil foundation pit deformation is summarized and the comprehensive suggestion value of its warning standard is put forward.Finally,based on the results obtained above,this thesis takes a deep silt foundation pit support in Guangzhou as an example to optimize the application.At the same time,the monitoring results of the retaining structure and the surrounding soil during the excavation of the foundation pit in the deep silt layer are verified with the case of the foundation pit support.The main conclusions are as follows:Firstly,based on the distribution characteristics and engineering characteristics of soft soil layer in Nansha area of Guangzhou and combined with the data of indoor soil test,the thesis analyzes and discusses the plastic and consistency characteristics of soft soil in Nansha area of Guangzhou as well as the relationship between water content,pore ratio and other physical and mechanical indexes through statistical charts,which provides powerful basic data support for the rapid engineering analysis of foundation pit support scheme in Nansha area of Guangzhou.For the first time,the relationship between compression modulus of soft soil in Nansha area of Guangzhou and four stiffness parameters of HSS constitutive is proposed.Secondly,on the basis of case statistics and geological condition analysis,the calculation and comparison of various working conditions were carried out by Lizheng deep foundation pit and Plaxis3 D analysis software.The setting of slope rate of top slope width and thickness of mixing pile wall,pile diameter of double row of piles distance between rear piles,width and thickness of reinforcement soil in pit,pile diameter of row of piles,number of anchor cable channels and number of supporting channels were obtained as well as the deformation and internal force of corresponding support forms.It provides a systematic solution for the selection of foundation pit supporting scheme in Nansha area of Guangzhou.Finally,based on a large number of engineering examples,using the method of mathematical statistics,the preset value and measured value of foundation pit monitoring are statistically analyzed,and the value methods of the main monitoring and control indicators in foundation pit engineering,such as horizontal displacement,horizontal displacement rate,vertical displacement,and support axial force,are discussed,and the value methods of four control indicators are proposed.On the basis of the analysis of a large number of engineering measured data and the verification of numerical calculation,combined with the evidence of out-of-limit cases,the value method of the four monitoring index control standards of horizontal displacement,horizontal displacement rate,vertical displacement and support axial force based on the influence factor is further verified,and the improvement suggestions are provided for the current foundation pit monitoring specifications.