| Utility tunnels can centrally manage all kinds of underground pipelines,and its construction has become a hot pot in many cities.But in the operations of constructed utility tunnel projects,the longitudinal uneven settlement of the tunnel itself and the transverse uneven settlement of the municipal road above the tunnel are becoming more and more prominent,which directly affect the safety of utility tunnels and the normal use of municipal roads.Furthermore,the foundation of a utility tunnel varies with its axis in mountain city,leading to more complicated uneven settlement problems.Therefore,based on a certain utility tunnel project which is under constructing in Chonqing,this essay combines field monitoring test,finite element numerical simulation and theoretical deduction to study the settlement characteristics of the utility tunnel and the fill alongside it,and put forward settlement calculation methods.This essay mainly conducts following jobs:(1)Based on a certain utility tunnel project and combined with the design data,construction characteristics and geological conditions of the project,the characteristics of longitudinal non-uniformity of the foundation and structural stiffness of the utility tunnel in mountain cities are summarized.Then the on-site monitoring test is carried out on the utility tunnel whose foundation consists of fill and rock,during which the settlement of the utility tunnel,the development of cracks and the settlement of municipal road are monitored.According to the results of the monitoring test,the longitudinal deformation law of the utility tunnel and the causes of the cracks in it are put forward.The influencing factors of the tunnel deformation are analyzed from the aspects of the uneven longitudinal stiffness of pipe gallery,the overall stiffness,the variation of foundation stiffness,the position of load and the buried depth of the tunnel.The monitoring test results show that the bending stiffness of the cast-in-place structure of the tunnel is greater than that of the prefabricated one,and the deformation of the cast-in-place structure conforms to the assumption of plane section.(2)In this paper,a simplified longitudinal settlement analysis model is established according to the project.Then,additional pressure caused by the rectangular ground load on the axis of the top of the utility tunnel is solved in a semi-infinite space,and the tunnel is assumed to be a beam on elastic foundation.The longitudinal deflection differential equations and the finite difference equations of the tunnel are derived.Combined with the characteristics of the tunnel,different bending stiffness of the prefabricated tunnel and the cast-in-place structure are given.The equivalent stiffness of the cast-in-place structure and the prefabricated tunnel were respectively calculated by directly solving the sectional moment of inertia and the longitudinal equivalent stiffness method.By using mathematical software programming to solve the finite difference equations,the longitudinal settlement curve of the tunnel is obtained.The calculation program in this paper is verified by comparing with relevant literature.The calculation results of different length of the tunnel are analyzed and the reasonable length of the tunnel is put forward.The reliability of the theoretical calculation method is verified by comparing with the longitudinal settlement calculation results of the three-dimensional finite element model of the utility tunnel in the monitoring test.(3)Based on the calculation method of longitudinal settlement of the utility tunnel deduced in this paper and the monitoring test results,the influencing factors of longitudinal deformation of the tunnel are further analyzed.By comparing and analyzing the deformation and internal force of the tunnel due to the uneven longitudinal stiffness under the action of local load and strip load,it is found that the uneven deformation mainly occurs in the precast section,and the internal force in the cast-in-place section structure is larger.Compared with increasing the structural stiffness of the tunnel,increasing the foundation stiffness can reduce the settlement of the tunnel more effectively.The control of ground load,the horizontal distance between the load and the tunnel and the buried depth of the tunnel have great influence on the settlement deformation of the utility tunnel.The theoretical calculation method proposed in this paper is used to predict the longitudinal deformation of the utility tunnel under the load of municipal road vehicles in the operation and maintenance stage.(4)Based on the field investigation in the construction process and combined with the design data,the analysis model of foundation pit filling settlement is established.According to the actual construction characteristics,the factors influencing the uneven settlement of the backfill soil in the foundation pit of the utility tunnel are analyzed and summarized as the compression modulus of the fill in the narrow backfill area at the side of the tunnel,the confining condition and the load condition of the fill.The confining condition consists of the bottom width of the foundation pit,the friction coefficient between the tunnel and fill,the fill thickness on the top of the tunnel and the slope rate of the foundation pit.The load condition includes the distribution width of the load on the side of the tunnel and the size of the adjacent load.Combined with the project data and the actual situation of the project,the value range of each influencing factor is defined.(5)Using ABAQUS,quantities of numerical models are established to analyze the influence of the compression modulus of fill in the narrow backfill area at the side of the tunnel,the confining conditions and load conditions on the settlement law of fill,and the construction measures to reduce the uneven settlement of the road surface above the tunnel are proposed.Combined with the analysis results of settlement influencing factors,the layered summation method which is corrected by the confining condition and load condition coefficients is proposed to calculate the maximum settlement of backfill pavement of utility tunnel foundation pit,and the formulas of correction coefficients is obtained by using regression analysis.Compared with the finite element simulation results of layerd fill,the calculated results of the two match well. |
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