| Due to its climate and geological conditions,the internal structure of tunnels in cold regions is facing the threat of periodic frost damage for a long time,leading to the formation of diseases such as cracking,peeling,water leakage,and cavity water accumulation and frost heave of tunnel lining,seriously reducing the service life of the tunnel.In order to deeply study the mechanism of frost damage and deterioration of tunnel lining in cold regions and the effectiveness of insulation and prevention measures,this article takes the Bapanshan Tunnel as a supporting project,and takes the tunnel lining in cold regions as the research object.Firstly,the law of frost damage and deterioration of tunnel lining in cold regions was studied through on-site research and in-situ testing;Then,a thermal fully coupled model based on near-field dynamics was derived,and the model was applied to the global sensitivity analysis of tunnel lining damage and a prediction model for lining frost damage deterioration was established;Furthermore,the freeze-thaw damage mechanism of the lining was analyzed from both macro and micro perspectives through physical similarity model experiments,and the spatial distribution and variation of freezing zone and frost heave force in cold region tunnels,as well as the mechanism of lining frost heave damage,were analyzed through numerical simulation;Finally,the anti-freezing effect of the insulation layer was analyzed and an optimization plan was proposed.The main research content and conclusions of this article are as follows:(1)Taking the Bapanshan Tunnel as a typical engineering example,through on-site monitoring and in-situ testing,the temporal variation patterns of wind speed,wind direction,environmental temperature,lining surface temperature,surrounding rock structure radial temperature,air flow field and temperature field in extreme environmental temperatures in the tunnel site area,as well as the deterioration patterns of tunnel lining structure cracking were analyzed.Qualitative analysis was also conducted on the form of tunnel frost damage deterioration in cold regions.(2)Based on the classical thermal-mechanical coupling equation and the generalized near-field dynamic thermal-mechanical coupling equation,and based on the principle of equivalent strain energy(free energy)density,the bond type near-field dynamic thermalmechanical complete coupling equation is derived.A hybrid model with direct coupling between the finite element domain and the near-field dynamic domain is established to solve the non-local problem of temperature crack deformation in tunnel lining structures.Based on a hybrid model of near-field dynamics and finite element analysis,numerical simulation analysis was conducted on the deterioration state of tunnel lining in cold regions,revealing the mechanism of structural performance degradation of tunnel lining in cold regions,and providing theoretical support for anti-freezing control measures of tunnels.(3)Using a mixed level orthogonal experiment,using the stress field,deformation,and cracking state of tunnel lining as indicators,the global sensitivity analysis method was used to analyze the global sensitivity of 8 factors on lining deterioration in cold regions,including tunnel lining position,wind temperature,local bias pressure,frost heave,lining thickness,back cavity,tunnel burial depth,and surrounding rock strength.Based on the sensitivity analysis results and combined with the experience of tunnel engineering in cold regions,an AHP fuzzy comprehensive evaluation prediction model was constructed.The risk relationship of freezing damage and deterioration in cold region tunnels was found by calculating the corresponding fuzzy comprehensive evaluation values.Compared with the traditional engineering analogy method,the judgment results are more scientific and provide a practical pre-evaluation method for operating tunnels in cold regions.(4)Based on the similarity criteria of temperature field,seepage field,and stress field,an indoor accelerated freeze-thaw cycle test system was designed to analyze the freeze-thaw damage mechanism of tunnel lining.The experiment ended at the 220 th freeze-thaw cycle and analyzed the changes in the apparent morphology,mass loss rate,and relative dynamic modulus of the lining from a macro perspective.The changes in the lining hole structure were analyzed from a micro perspective,and the freeze-thaw damage mechanism of tunnel lining in cold regions was comprehensively revealed from a macro and micro perspective.A freeze-thaw damage prediction model was established based on Weibull distribution,and the evolution process of tunnel lining freeze-thaw damage was derived,Predict the service life of tunnel lining under freeze-thaw cycles.(5)Based on the mathematical model of tunnel lining water thermal coupling frost heave,the spatiotemporal evolution law of freezing zone and frost heave force was analyzed through numerical simulation.The temporal and temperature effects of surrounding rock physical and thermal parameters were considered,and the mechanism of tunnel lining frost heave damage was analyzed.The control variable method was used to discuss the movement law of the freezing front and the frost heave deterioration law of the tunnel lining.The results were compared and fitted with the indoor accelerated freeze-thaw cycle test results,further revealing the deterioration state of the service performance of tunnels in cold regions.(6)Taking the climate environment of the Bapanshan Tunnel as an example,a comprehensive analysis was conducted on the insulation effect of the insulation layer of the tunnel in cold regions.Analyzed the laying methods of different insulation layers,thermal conductivity of different insulation materials,thickness of different insulation layers,and insulation effects under different temperature conditions based on the range of heat regulating rings;Based on the movement law of the frozen front,the freezing depth parameter in the calculation formula for the thickness of the insulation layer was modified.The laying length of the insulation layer was calculated using the Heichuan Xifan empirical formula,and the safety coefficient of the tunnel lining structure was verified.The results show that the circumferential radial depth of the heat transfer ring is significantly reduced after the insulation layer is installed,which indicates that the convection heat transfer of the cold air is suppressed.The insulation effect of the insulation layer with different settings is in the order of double layer,wall mounted,sandwich composite,and off wall.When setting up an insulation layer,it is recommended to choose a wall mounted insulation layer.The thickness of the insulation layer should not be less than 5.5cm,and the thermal conductivity of the insulation material should be 0.025-0.04(W/m·k)and laid throughout the entire length.When the average temperature is below-17℃,additional insulation measures should be taken to ensure the anti-freezing ability of the tunnel structure. |
