Study On Safety Analysis And Monitoring System Of Open Cut Tunnel In Construction And Operation

In recent years,with the increasingly serious problems of urban traffic congestion and shortage of land resources,the construction of urban underground expressway,that is,the development of urban road network from plane to three-dimensional expansion,has become one of the effective ways to solve the above contradictions.The underground expressway generally adopts super large section rectangular structure,the type is more complex,the buried depth is relatively shallow,and most of them are constructed in the form of open excavation tunnel.Compared with shield tunnel,the structural stress characteristics and structural health diagnosis system of open-cut tunnel are more complex,and the related research is rare.In this paper,combined with an engineering example,the structural mechanical response law of the whole life cycle of open-cut tunnel is studied by using ABAQUS numerical analysis software,and a suitable structural health monitoring system is established.The main elements include:Aiming at the "pit in pit" foundation pit of open excavation tunnel,a three-dimensional finite element model of soil,retaining pile(wall),sup porting structure system,column and engineering pile is established.The deformation characteristics of three typical section types of foundation pit during construction and the displacement law of pile and column system are analyzed.The results show that the excavation depth of internal and external foundation pit is different.The deformation characteristics of open excavation tunnel foundation pit are more complex than those of general building foundation pit.The factors affecting the comprehensive stiffness of the retaining structure of open-cut tunnel foundation pit are analyzed by orthogonal simulation test.The effects of six factors,such as the stiffness of the outer connecting wall,the stiffness of the inland connecting wall,the stiffness of the concrete support,the vertical spacing of the steel support and the stiffness of the column,on the deformation of the retaining structure and the displacement of the "one column,one pile" uplift are taken into account.The results show that the stiffn ess of the connecting wall in the interior has the greatest influence on the former.The vertical spacing of steel braces has the greatest influence on the latter.In view of the internal force effect of open-cut tunnel structure in elastic stage,the typical parameters such as traffic load,section type and pile arrangement are selected as variables for numerical modeling and analysis.The results show that:(1)under vehicle load,the most sensitive part of structural vibration response is the middle position of the main lane span.When the speed increases to a certain extent,the vibration response of the structure tends to jump,while the maximum vertical displacement and dynamic stress increment of the structure increase significantly when the vehicle is overloaded;(2)due to the "strengthening" effect of the side wall,partition wall and middle wall,the maximum tensile stress and transverse settlement of the structure are concentrated in the main lane position,where the structure is the most unfavorable stress position;(3)the arrangement of engineering pile can effectively reduce the maximum settlement value of the longitudinal length direction of the section,and the effect of infill arrangement engineering pile on the small section structure without ramp is good,and the effect on the large section structure with ramp is general.In view of the internal force effect of open excavation tunnel structure in elastic-plastic stage,lateral earth pressure,overlying earth pressure,vehicle load and subway load are selected as load combination,and the influence of wall damage is taken into account.Two kinds of section types with and without engineering pile are compared,and the development of plastic joint is analyzed.The results show that the bearing capacity of the tunnel structure is significantly enhanced when the engineering pile is set up,and the damage of the side wall has the greatest influence on the bearing capacity of the structure.Based on the numerical calculation results and the anal ysis of typical accidents and diseases,the structural health monitoring scheme of open excavation tunnel in Nantong Seyuan Road during construction period and operation period is worked out.on this basis,the health monitoring system of open excavation tunnel structure is established,and the integration and sharing principle of construction monitoring and operation monitoring system,the integration of multi-level safety assessment and early warning and emergency decision are put forward.