| The problems of complex multi-field coupling of surrounding rock and lining frost heave often exist in hydraulic tunnels in cold region.To solve the problems of rock mass and lining frost heave caused by the phase change of pore water under low temperature in cold area,this paper relied on the diversion tunnel project of a hydropower station in Xinjiang and adopted the combining methods of field monitoring,theoretical derivation and numerical simulation.Based on the temperature monitoring results,a thermo-hydro-mechanical coupling model at low temperature and a rock-lining frost heave model under the condition of water-ice phase change were established respectively.The effects of water-ice phase change on the coupling effect and the frost heave characteristics of surrounding rock under the phase change condition were analyzed,and the change rules of lining physical field under different working conditions were studied.Finally,some reasonable prevention and treatment measures were put forward in view of the freezing damage phenomenon of cold region tunnel.The main conclusions are as follows:（1）The inner temperature of the surrounding rock and the cavity ambient temperature of the cavity are monitored by placing temperature measuring points in the diversion tunnel.The results show that the maximum freezing depth of surrounding rock is 2.35m,and the cavity temperature varies sinusoidally over a period.The results can be applied as a temperature boundary for subsequent numerical analysis.（2）The effect of water-ice phase change on the thermo-hydro-mechanical coupling process is analyzed.The results show that in the coupling process of 200 days,the influence range of cave ambient environment on the surrounding rock temperature is about 5m,and the negative temperature zone and the freezing depth increases with the freezing time.The water-ice phase change directly affects the freezing depth of surrounding rock during the thermo-hydro-mechanical coupling process.The phase change reduces the freezing depth and delays the occurrence time of the maximum freezing depth.The freezing depth considering the water-ice phase change is closer to the measured value.The frost heave caused by the water-ice phase change increases the stress and deformation of the surrounding rock obviously.The maximum principal stress and vertical strain of the surrounding rock are 0.385MPa and 0.038%without the phase change,and 0.475MPa and 0.041%with the phase change.The change of water-ice state caused by the change of ambient temperature in the surrounding rock seepage field changes the size and direction of pore water velocity.The maximum seepage velocity is 1.15×10-11m/s in the absence of phase change,and1.22×10-11m/s in the presence of phase change.The maximum seepage velocity appears near the waist to the bottom of the arch.The drainage measures should be taken according to the regulations.（3）The analytical solution of frost heaving force based on the global frost heaving model is derived and compared.And the frost heave force values of the inner and outer frozen layers of surrounding rock are calculated to be 10.856MPa and 4.002MPa respectively.The rock-lining structure model considering water-ice phase change is established to analyze the frost heave characteristics of surrounding rock.The results show that the maximum freezing depth of the surrounding rock is calculated to be 1.66m,and the minimum lining temperature is-12.7℃.Since the freezing depth change rate is affected by the surrounding rock temperature gradient and ambient temperature,the freezing depth gradually decreases until it becomes a positive temperature zone after 130 days freezing.The absolute value of frost heave displacement increases first and then decreases,and the maximum settlement displacement is 1.96mm,and the maximum frost heave stress is 0.634MPa.Compared with before frost heave,the displacement and stress after frost heave increase greatly.（4）The physical field properties of lining structure within 200 days are analyzed.The results show that the hydration heat of concrete and ambient temperature obviously affect the stress and displacement of lining.The maximum principal stress of the lining is 8.588MPa and the maximum displacement is1.929mm.The higher the temperature of the lining itself,the greater the stress and displacement difference between the inner and outer sides.Lining at low temperature is more sensitive to positive temperature.Writing the lining model script,the temperature,stress and displacement of the lining under different working conditions are studied with variable parameters,and the stress field of the lining under different working conditions is obtained.The results show that the sensitivity of the stress field state of lining to lining thickness,lining stiffness and cavity temperature is as follows:cavityt temperature>lining stiffness>lining thickness. |
PDF Full Text Request