Risk Analysis And Control Of Diaphragm Wall Retaining Structure System In Clayey Soil

In recent years,with the deepening of urbanization in China,the difficulty of foundation pit engineering is increasing,and more and more of them are in sensitive environment.Underground diaphragm wall support structure with multiple internal supports has gradually become a common support form for deep foundation pit engineering in urban built-up areas.Although it has been widely used,the evaluation and design rationality of this type of support still need to be improved,which is based on the in-depth study of rock and soil mechanics parameters and existing design methods.When excavation of deformation-sensitive stratum,especially in soft clay area,the uncertainty of support structure risk is further magnified.In view of this problem,it is necessary to carry out the character analysis of underground diaphragm wall supporting structure system in soft clay area.Only when the factors affecting the risk of underground diaphragm wall supporting structure are deeply understood,can the development of this kind of foundation pit deformation be predicted accurately and the risk of supporting structure system be effectively controlled.Hangzhou area has a typical soft clay geology,through the analysis of the relevant engineering cases in this area,systematic analysis of the risk of underground diaphragm wall supporting structure system in soft clay,and put forward the corresponding specific solutions,providing reference for the design of the foundation pit of underground diaphragm wall supporting structure in similar soft soil area.Numerical back analysis is established in this paper,through soil parameter selection of small strain hardening model,based on the underground continuous wall supporting structure of each failure mode,using the grey correlation design concept,analyses the various controllable geometry parameters on the sensitivity of the supporting structure safety degree,then focuses on the underground continuous wall in the design of supporting structure is of all kinds of uncontrollable risk and the effect of parameters on the supporting structure system and the relationship between and controllable geometry parameters,put forward a kind of based on correlation analysis of underground continuous wall supporting structure design method of robust uncontrollable parameters on the supporting structure,in order to solve problems,the influence of the main content of this paper is as follows:(1)The narrow and long deep foundation pit of a subway station in Hangzhou is introduced in detail,and the two-dimensional and three-dimensional finite element models of soil,underground diaphragm wall,horizontal and vertical support systems,and reinforced piles are established for this project.Based on existing engineering in the evaluation of the use of small strain hardening model of soil parameter selection tends to experience,lead to feedback to the geometric parameter adjustment is not precise design units,through the numerical inverse analysis to analyze typical project in soft clay area of Hangzhou,established a set of suitable for engineering application in soft clay area small strain hardening soil parameters selection suggested values of the model.(2)Based on the design concept of the grey relational multi-objective optimization algorithm,the sensitivity weight index of the geometrical parameters of the underground diaphragm wall supporting structure in the typical soft clay area of Hangzhou was found based on various failure modes of the underground diaphragm wall supporting structure,and the optimal solution of the geometric parameters was obtained.The main failure modes of underground diaphragm structure include uplift failure mode,overturning failure mode and lateral movement failure mode of supporting structure.For three types of failure modes combined with reliability theory,the optimal solution based on evaluation system of single objective is obtained.According to each single objective to establish a set of geometric parameter sensitivity index weights,(geometric parameters,including underground continuous wall deep,underground continuous wall,wall thickness,reinforcement pile length,and the sensitivity of the support system corresponding to each support weight)and using grey correlation method of multi-objective optimization for multi-objective geometric parameters of the optimal solution.Therefore,a set of geometric parameter selection design process based on the optimization of structural stability and economic cost was established by the grey relational multi-objective optimization method.Subsequent research has shown that the design process is suitable for little not controllable parameter variance(not controllable parameters in this paper mainly includes: rock mechanics parameters,structure,construction parameter,the live load,etc.),large uncontrollable parameters that may affect the risk of the underground continuous wall supporting structure system,and the design of geometrical parameters,so it is necessary to not controllable parameter analysis of the influence of the supporting structure.(3)In the whole life cycle of underground diaphragm wall supporting structure system,uncontrollable parameters mainly include rock and soil mechanics parameters,structural construction parameters and live load parameters.Three parameters as the risk of foundation pit engineering,the project characteristic of the need to distinguish them in detail with the examples of typical project in soft clay area of Hangzhou,through the orthogonal experiment method to the failure modes of various types of supporting structure as the objective function,to determine the three types of parameters and their corresponding variance on the influence of the underground continuous wall supporting structure system of risk degree.(4)Based on the characteristics of various uncontrollable parameters,the geotechnical robust design method was proposed,and the economic cost of geometric parameters was introduced into the robust design.Based on the two objectives of standard deviation of failure probability and economic cost,the NGSA-II multi-objective optimization algorithm was adopted to solve the geometric parameter optimal solution of underground diaphragm wall supporting structure design.In addition,in the robust design,in view of the large uncertainty of the live load parameters and the fact that the variance cannot be accurately calculated,a relational multi-objective optimization method is proposed to optimize the variance of the load parameters,and the construction unit strictly controls the load parameters in exchange for a better solution of geometric parameters.