Seismic Performance Analysis Of Prefabricated And Cast-in-place Combined Lining For Double-layer Open-cut Tunnel With Large Section

With the extension of transportation system,not only the construction of highway and railway in mountainous areas is confronted with the problem of deep excavation and high filling,but also the demand for large-section open-cut tunnels in urban infrastructure construction is increasing.In recent years,the construction of open-cut tunnels is developing towards the direction of large-section,large buried depth,complex structure and complicated conditions,which brings great challenges to design and construction.Compared with underground structures such as shield tunnels,large cross-section open-cut tunnels have very different mechanical characteristics.Therefore,the existing theories and design methods can not be directly applied to the design of large cross-section open-cut tunnels currently.The selection of open-cut tunnels under complex load conditions and the study of structural dynamic characteristics are urgently needed.In this paper,three types of open-cut tunnels with single-arch,double-arch and double-deck,box-type and double-deck cross-sections are established by using plastic damage constitutive model of concrete.Firstly,the response characteristics of cast-insitu monolithic tunnels with different cross-section types under static and dynamic loads,the development law of structural damage and the variation characteristics of strata are analyzed.The dynamic response and mechanical characteristics of the structure under different depth of burial are studied by setting different depth of burial.In addition,the restraint effect of steel bars on the development of structural damage is studied by establishing reinforcement model and non-reinforcement model.It is considered that the existence of steel bars plays an important role in reducing the degree of structural damage.It is revealed that in the dynamic analysis of underground structures,considering the role of steel in the process of modeling is helpful to improve the accuracy of numerical simulation results.In view of the shortcomings of the existing methods for evaluating the seismic performance of underground structures,the post-processing program of the model is compiled by Python language.With the help of the plastic damage constitutive model adopted by tunnel structures,the damage results are identified and processed in different time periods of seismic wave action,thus changing the shortcomings of qualitative description of structural damage in the past.Statistical damage area and undamaged area are realized,and the curve of damage area ratio changing with time is drawn,which provides assistance for structural damage analysis under earthquake action.Based on the above research,the corresponding two-dimensional model is established to explore the way of assembling single-arch tunnel and double-arch tunnel.The mechanical performance and dynamic response characteristics of the prefabricated cast-in-situ combined open-cut tunnel under static conditions are studied,and the stress variation characteristics of different components under different thickness of overlying soil are summarized.The seismic performance of the prefabricated cast-in-situ combined open-cut tunnel and the cast-in-situ integral tunnel are compared and analyzed.It is concluded that reasonable assembly can greatly improve the seismic performance of underground structures.At the same time,the rationality of using structural damage development curve as a supplement to structural seismic performance evaluation criteria is further verified.