Study On Mechanical Behavior And Structural Response Of Foundation Pit Construction Of Ultra Deep Working Shaft

With the rapid development of China's modernization construction,more and more deep foundation pit projects appear,the excavation depth and scale are more and more large,and the design is more and more difficult.In the design of deep foundation pit,the calculation of earth pressure is the core problem,whether it is accurate and reasonable is directly related to the safety and economy of foundation pit engineering.Therefore,the calculation mode of earth pressure is the frontier problem which needs to be solved and studied urgently.At present,the elastic fulcrum method is adopted in the code to calculate the support structure,which regards the earth pressure acting on the back of the wall as constant load During the step excavation,the back of the wall remains constant in the same working condition,which is not consistent with the actual situation.Therefore,it is necessary to study the dynamic change law of the earth pressure of the ultra deep foundation pit and explore new design ideas and methods of the ultra deep foundation pit.At the same time,in order to meet the requirements of shield assembly,starting and hoisting,the short-time load on the pit side is frequent,and the construction conditions are more complex.In the design process,the short-time load is simplified as permanent load,which makes the design value of the support structure deviate from the actual value greatly.Therefore,a deeper and systematic understanding of the internal force evolution characteristics of the deep support structure under the short-time load is needed And the law of deformation is undoubtedly an important part and a new growing point of the development of the design and calculation of deep foundation pit support.In this paper,based on the research background of the South and North Bank of Jinan Yellow River tunnel project,based on the field measured data and the theoretical analysis,the dynamic formation and change rule of the earth pressure in the ultra deep foundation pit are studied.Through the combination of field test and numerical simulation,the stress and deformation rule of the underground continuous wall + internal support structure under the short-term load are studied The main research contents and results are as follows:1.Through the method of theoretical analysis and field measurement,the influence of the bending deformation of diaphragm wall and the excavation of foundation pit on the dynamicearth pressure change in the process of ultra deep foundation pit construction is studied,and the shortcomings of the conventional calculation mode of earth pressure behind the foundation pit wall are pointed out.2.Based on Rankine's earth pressure theory,considering the non-linear distribution of earth pressure along the depth of the foundation pit,a six degree polynomial is used to fit the measured horizontal displacement curve of the diaphragm wall,and the earth pressure behind the wall is back calculated to explore the formation process of the dynamic earth pressure in the process of foundation pit construction,as well as the deformation of the earth pressure with the excavation depth of the foundation pit and the bending of the diaphragm wall The law of dynamic change.3.Through the method of field test,the underground continuous wall + internal support structure is studied,and the detailed intelligent monitoring scheme is formulated.Through the omnidirectional real-time displacement tube,reinforcement meter and axial force meter,the underground continuous wall,concrete support and steel support are monitored in real time.Combined with the detailed construction conditions,the monitoring data are processed and analyzed,and the underground continuous wall + internal support in the silty clay layer is obtained The law of stress and deformation of braced structure under short-time load: the location of short-time load has great influence on the deformation of diaphragm wall,but the middle partition wall will greatly weaken the effect of short-time load.After the removal of short-time load,the diaphragm wall will rebound.The measured results show that the deformation recovery of diaphragm wall can reach 30.6% ~ 54.6%,and the larger the deformation,the more the recovery The smaller the deformation,the larger the recovery.4.Based on the finite element numerical simulation method,the mechanical response analysis of the underground continuous wall + internal support structure under the short-term load is carried out,and the deformation and internal force calculation results of the underground continuous wall,concrete support and steel support are analyzed,and the change rules are summarized,and the comparison analysis with the measured results is carried out.