Adaptability Evaluation And Optimization Design Of Somposite Support Structure Of High Temperature Diversion Tunnel

High temperature and heat damage not only increases the difficulty of tunnel excavation and thus affects the construction period,but also poses a threat to the life safety of construction personnel.The temperature stress not only affects the durability of the concrete support structure,but also affects the stability of the support structure.In serious cases,it will lead to the failure of the support structure and affect the stability of the surrounding rock.Therefore,it is very important to study the mechanical characteristics of the supporting structure and to optimize the design of the supporting structure.In this paper,based on a hydropower station in Xinjiang,the temperature distribution,displacement variation and mechanical characteristics of surrounding rock and composite supporting structure under high temperature environment are systematically compared by field monitoring test,steady state and transient numerical simulation,single factor sensitivity analysis,etc.The main work and conclusions are as follows:(1)The temperature field and stress field of high ground temperature composite supporting structure are simulated by finite element method,and compared with the results of tunnel field monitoring test.The EPS composite support structure has the best thermal insulation performance,the three kinds of lining structure have the largest circumferential stress at the vault,in contrast EPS the composite lining has the smallest circumferential stress,its value is 0.40 MPa,EPS the composite support structure is subjected to the force characteristics are the best;there is a certain error between the results of the numerical simulation and the field monitoring data.the relative difference between the temperature simulation value and the measured value is 6.25%,and the minimum is 0.11%.the relative error between the stress simulation value and the measured value is large,but the magnitude and distribution area of the stress are basically consistent.the simulation results can reflect the actual temperature and stress distribution during the construction period.(2)By using finite element method,the transient numerical simulation of high ground temperature composite support structure is carried out,and the influence of each part of the composite support structure on the temperature,displacement and stress of surrounding rock is analyzed,so the adaptability evaluation of the composite support structure is carried out: from the temperature point of view,the maximum time period of thermal insulation of composite support structure is secondary lining construction;from the displacement angle analysis,the shotcreting layer can play a supporting role in time after the completion of construction,which can only prevent the large change of displacement in the hole wall within 2 m range,and it is also necessary to add secondary lining;From the stress point of view,after the completion of the spray layer construction,the tunnel vault,arch waist and arch bottom three The maximum principal stress changes from compressive stress to tensile stress in two places where the arch roof and the arch waist are affected by the bearing of the spray layer.The maximum tensile stress at the arch bottom changes from compressive stress to tensile stress.On the 10 th day after the completion of thesecond lining construction,the lining plays a relatively low supporting role.On the 60 th day,the stress of surrounding rock hardly changes;Angle analysis,spray layer can limit the plastic zone change speed,but the support capacity is limited,need secondary lining to limit the expansion of the plastic zone of surrounding rock,the composite support structure is gradual to inhibit the expansion of plastic zone of surrounding rock.(3)To optimize the design of the thickness and arrangement of the composite support structure,the main conclusion is that the thickness of the spray layer is within 10-12 cm,and the thickness has relatively little influence on the annular stress,so it is the optimal thickness selection interval.The change of heat insulation layer thickness has little influence on the temperature difference between inside and outside.The thickness of the secondary lining has little influence on the annular stress,so it is suggested to select the design thickness of the secondary lining within the range of 40-45 cm.By comparing the two types of composite support structures,it can be concluded that the displacement variation of surrounding rock of the wall-attached structure is larger than that of the interlayer structure,and the reason is that the shotcrete structure does not play a temporary supporting role in the optimal time.The maximum plastic strain of the surrounding rock of the wall type is larger than that of the sandwich type,and the distribution is dense.