Research On Mechanical Characteristics And Influencing Factors Of Retaining Structure Of Circular Ultra-deep Shaft

Recently,with the rapid development of urban infrastructure,a large number of tunnel projects have been carried out in many places in China,and the scale and depth are also increasing.When constructing in deep underground space,it is necessary to excavate ultra-deep shield working wells,and circular section is usually used in its plane design.In this kind of circular shaft applied to ultra-deep excavation,there are few engineering cases and systematic studies of its retaining structure at present.But when excessively deep excavation,if the analysis of the retaining structure is not reasonable,it is easy to cause major engineering accidents.Therefore,it is of great significance to study the mechanical characteristics of its retaining structures.In view of this,based on the circular shield shaft of a large tunnel project,the monitoring data of the project are analyzed,the three-dimensional continuum finite element model is established by MIDAS/GTS NX finite element software,and the mechanical characteristics of the retaining structure during excavation are systematically studied.The three-dimensional models of retaining structure and spring are set up to calculate the deformation and internal force of retaining structure by using the three-dimensional "m" method,and compared with the results calculated by the three-dimensional continuum finite element model,then the agreement with the measured data is discussed.Finally,based on the model,the influence of rock and soil layer difference,diameter of circular shaft,thickness of support structure and circumferential rigidity of diaphragm wall on circular ultra-deep retaining structure is studied,and some difficult problems in engineering design are solved.The main findings are as follows:(1)Based on the field monitoring data,the characteristics of deformation of retaining structure,stress of reinforcing steel bar and earth pressure behind the wall during the whole construction process are analyzed and summarized.(2)The displacement,vertical bending moment and circumferential stress of the retaining structure are calculated and analyzed by the three-dimensional continuum finite element model and the three-dimensional "m" method respectively.The results show that the deformation and internal force of the diaphragm wall with circular shaft are asymmetrical due to the influence of construction and geological conditions,and the maximum displacement and vertical bending moment occur in the middle of wall and near the top of rock respectively.(3)The calculated results of the three-dimensional "m" method are in good agreement with the monitoring data and the variation law of the stress and deformation of retaining structure are basically consistent.By comparing with the results of the three-dimensional continuum finite element model,it is found that the calculation results of the three-dimensional "m" method are closer to the actual monitoring data.(4)The influencing factors of retaining structure of circular ultra-deep shaft are discussed.The analysis results show that the asymmetry of soil layer has a significant effect on the radial displacement;the rock properties only have obvious influence on the maximum vertical bending moment;the shaft diameter,underground diaphragm wall thickness and circumferential stiffness have great influence on the deformation and internal force of supporting structure.