| Establishing a damage constitutive model of rock under high temperature and load is very important for studying the thermal-mechanical coupling characteristics of hydraulic tunnel surrounding rock under high ground temperature.Numerical simulation and theoretical deduction were used to determine the regional range of temperature field change and stress field change after excavation of a hydraulic tunnel in a high geothermal environment.The mechanical response model of rock damage induced by temperature in underground engineering was deduced,and the mechanical response characteristics of surrounding rock of a high geothermal hydraulic tunnel under different working conditions were studied.Some conclusions are drawn as follows:(1)Thermal-mechanical(TM)coupled numerical simulation of surrounding rock of high temperature hydraulic tunnel.The value range of stress field variation caused by excavation can be determined by analytic solution,i.e.three to five times the diameter of the tunnel.For the range of temperature field variation caused by excavation,the calculation radius R of the surrounding rock corresponding to the stable temperature of the interface can be determined by studying the temperature of the interface between the surrounding rock and the lining structure.The range of numerical model can be determined by synthesizing the influence of temperature field and stress field.(2)Evolution equation and constitutive model of rock damage induced by high temperature.The constitutive model of rock subjected to load alone can be compared with the experimental results.The strain-damage evolution curves of rocks under various confining pressures are all of the inverted "S" type,and the stress-damage evolution curves of rocks under various confining pressures are of the horizontal "parabolic" type.The stress-strain curves of rock damage under the combined action of temperature and load are in good agreement with the experimental curves at the pre-peak rising stage and the post-peak descending stage.The damage evolution process of rock under the combined action of high temperature and load can be divided into initial stage,transition stage and stable stage.The initial damage caused by high temperature at 100,200,400 and 600 degrees is 0.2,0.3,0.35 and 0.4,respectively.The damage caused by high temperature mainly concentrates in the initial stage of damage evolution,and has little influence on transition stage and stable stage.(3)Thermal-mechanical(TM)coupled numerical analysis of surrounding rock of hydraulic tunnel based on constitutive model of strain softening induced by high temperature.The stress in the surrounding rock of circular tunnel under thermal-mechanical coupling is obviously concentrated.The stress in the waist of tunnel arch is larger than that in other parts of tunnel wall,and its maximum stress is 17 MPa.The excavation face of the tunnel and the surrounding rock mass have obvious displacement to the space of the tunnel,and the displacement at the vault reaches the maximum.The plastic zone of surrounding rock mass under load and temperature eventually extends to a stable "butterfly" distribution.The influence of deep temperature of tunnel surrounding rock on the circumferential stress at the top,waist and bottom of tunnel wall should be considered.The deeper the tunnel is buried,the greater the circumferential stress and displacement of the tunnel wall,and the most obvious trend is the circumferential stress at the arch waist.The influence of lateral pressure coefficient on the circumferential stress and displacement of the arch waist and its vicinity is more serious.When the lateral pressure coefficient increases,the change of vault and waist is the most dramatic,but the change of waist and its vicinity is small.Therefore,in view of various construction environments of underground engineering,corresponding technical measures should be taken according to local conditions and combined with the corresponding research results. |
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