Temperature Field And Deformation Analysis Of Rocks Surrounding Seasonal Cold-region Tunnels

With the revitalization of the northeast industrial base and the implementation of westerndevelopment policy, the railway and road nets are expanding from east to west and from southto north. Yet the regions are almost high latitude or high elevation which belongs to seasonalfrozen soil region. The new challenge, freeze damage, will arise when the tunnel engineeringare built in these areas. This paper takes Yuximolegai tunnel as an example. A series ofresearches on temperature field and the stability analysis of surrounding rocks were carriedout for seasonal cold region using field test, analytical solution, physical test and numericalsimulation. The study can provide some guide significance for the construction of seasonalcold region tunnel.(1) The temperature laws of air and surrounding rocks of Yuximolegai tunnel areobtained by field measurement. The fitting analysis of temperature data of air can providebasic data for analytical calculation and numerical simulation. The frost depth can beapproximately obtained based on temperature measurement of surrounding rocks, which canprovide the necessary parameters for stability analysis of surrounding rocks. The temperaturemeasurement results can verify the numerical simulation results. The distance with insulationlayer can be determined by analyzing the temperature law of different sections.(2) The mathematic model of the temperature field of cold region tunnel is establishedbased on plane assumptions, which contains insulation layer, lining and surrounding rocks.The insulation layer is supposed to play a very good role. Then Laplace integral transfer andDenIsger inversion method are used to solve this model. The analysis for temperature field ofYuximolegai tunnel was carried out and the corresponding change law was obtainedaccording to the field measurement. The results show that the5cm thick insulation is notenough to stop frozen damage. The condition that the temperature at the outer edge of liningis greater than equal to zero is as the criterion. According to this criterion, if Yuximolegaitunnel is protected from frozen damage, at least19cm thick insulation layer is laid withoutother protective measures by trail calculation. Besides, the sensitivity analysis for heattransfer coefficient, annual average temperature and formation temperature is carried out andthe following conclusions are obtained: the effect of heat transfer coefficient on temperaturefield of tunnel is small; the thickness needed in Yuximolegai tunnel is determined underdifferent annual average temperature and formation temperature. The study can providecertain guide and theoretical basis.(3) Temp module in Geo-studio software is selected to calculate temperature field ofYuximolegai tunnel with and without insulation layer. The results of numerical simulation agree with field measurement in the same place when no insulation layer is installed. Thereliability of parameters is verified. When5cm insulation layer is installed, the calculationresults show that the effect of stopping the subzero temperature transfer is good, but thethickness is not enough to clear up frozen damage and the frozen depth is still0.4m. Based onthe whole and piecewise fitting results of freezing front of above two conditions, thecorrelation coefficient of whole fitting is large, but it can not contain all information offreezing front. The piecewise linear fitting is carried out for different materials, respectively.The following conclusions are obtained: the freezing front of the floor expands fastest. Thesecond is spandrel. And the slowest position is arch. The expanding speed of freezing front inlining is faster8~10times than that in surrounding rocks. The freezing range in the secondcycle is a little larger than that in the first cycle. When the insulation layer is installed, theexpanding speed of spandrel is fastest and its range is largest. According to above analysis,the spandrel and floor are both regarded as dangerous section to analyze the insulation layerthickness of Yuximolegai tunnel.21cm insulation layer can stop tunnels from frost damagewithout other measures.(4) Based on some assumption, the analytical solutions for stress and deformation ofseasonal cold-region tunnel are performed. The frost strain is regarded as tensile strain. Thedeficiencies of constitutive equation are improved. The no displacement position induced byfrost exists according to the direction of frost deformation and its iteration method is given.Firstly, based on the modified constitutive equation of frozen surrounding rocks, the stressfield of cold region tunnel is solved under no equal pressure. The stress fields of lining andsurrounding rocks are analyzed under different lateral pressure coefficients and angles,respectively. Then, the analysis of stress and deformation under hydrostatic pressure field ispreformed, including three possible situations. The sensitivity analysis is carried out whenplastic radius is smaller than frozen radius. The results can explain the influence of parameterson stress field and plastic zone. At last, the elastic melting model of frozen surrounding rocksis established according to the condition where no plastic zone occurs. The melting modelconsiders volume change and then the stress field of surrounding rocks is obtained aftermelting. Based on the above analysis, the stress and deformation of Yuximolegai tunnel aresolved when frost or melting happens.(5) According to similarity theory, the temperature field and frozen force of seasonalcold region tunnel are studied by physical test. The whole test device contains model body,boundary temperature control system, air temperature simulation system, temperature controlsystem and monitoring system. The tests are divided into two groups,5cm insulation and noinsulation. The temperature amplitude in test is lower than the measurement data, but it is still seen that insulation layer can stop subzero temperature transfer well and the average blockingrate reaches86.5%. When no insulation layer is laid, the frozen depth is about2m.While thefrozen depth is changed to0.5m. In test, the largest radial and circumferential frozen forcesare0.29MPa and0.275MPa, respectively. The largest circumferential strain is used tocalculate the largest frozen force,0.613MPa. The average largest frozen force in otherpositions is0.511MPa. The result is larger than the data monitored by stress tense. It is thereason that the thickness of stress tense reaching1.1cm causes the result to become small.Besides, the results calculated by strain are solved based on the assumption of circle section.(6) Temperature measured in field is compared with the results of numerical simulation,model test and analytical calculation, and the deviation is analyzed. Besides, the relationshipof the lowest temperature is obtained by analyzing the temperature at the outer edge of liningusing numerical simulation and analytical calculation. At last, the frost force in field iscompared with the result of model test.