| In response to the severe frost damage that has been occurring continuously in the tunnels in seasonal frozen area at home and abroad,this paper studies the tunnel engineering in seasonal frozen area from two aspects of frost heaving mechanism and anti-freezing measures through the methods of theoretical analysis,numerical simulation and field monitoring,The main conclusions are as follows:(1)In the process of tunnel construction in seasonal frozen area,due to the construction defects caused by construction collapse and uncompacted over excavation and backfilling,the space of stagnant water is formed between lining and surrounding rock,resulting in frost heaving force of stagnant water,which has a serious impact on the safety and stability of the tunnel structure.This paper optimized the shape of space of stagnant water into a semi-ellipsoid which is more inline with the engineering practice,and carried out theoretical derivation under three-dimensional conditions,and put forward a new calculation method of frost heaving force of stagnant water.Based on the local deformation theory,the calculation method of frost heaving force of stagnant water was derived and then verified by numerical simulation.The results show that the calculated values of theory in this paper and that of numerical simulation basically agree,and the values of theory in this paper are on the conservative side,which means that the method of calculating the frost heaving force of stagnant water of tunnels in the frozen season is reasonable and can be used in actual projects.In addition,a parameter sensitivity analysis of the depth of ice accretion,the elastic resistance coefficient of the surrounding rock and the elastic resistance coefficient of the lining,which affect the value of frost heaving force of stagnant water,was carried out using single factor analysis,and corresponding design and construction recommendations were put forward.(2)Based on the overall frost heaving model of broken freeze-thawing lithosphere,the calculation method of the overall frost heaving force of the horseshoe-shaped tunnel with broken surrounding rock in the seasonal frozen area was proposed,and the rationality of the method was verified by field measurements.A sensitivity analysis of the factors influencing the overall frost heaving force of broken freeze-thawing lithosphere of tunnels in seasonal frozen area was conducted to provide reasonable suggestions for the construction and operation of tunnel projects in seasonal frozen area.Finally,relying on the Yushuchuan Tunnel,the safety of the lining structure was analyzed based on the newly established overall frost heaving model.When the freezing depth of the plain concrete lining section of the tunnel reaches 0.3m,and the freezing depth of the reinforced concrete lining section of the tunnel reaches 0.7m,the minimum value of the safety factor of the tunnel structure is less than the minimum value allowed by the code.Based on this,we established management grades for monitoring the safety of plain concrete lining and reinforced concrete lining structures in broken rock tunnels in seasonal frozen area and proposes monitoring frequencies to achieve early warning forecasts of frost damage in broken rock tunnels and to ensure the operational safety of the tunnels in seasonal frozen area.(3)This paper presented a new type of off-wall corrugated steel plate insulation lining.The method is to fill polyurethane insulation in the middle of double corrugated steel plates and leave a sealed air layer for off-wall application between the tunnel lining and the insulation lining layer.It has the advantages of easy construction,reliable waterproof performance,and can prevent concrete from falling blocks and improve the service life of polyurethane materials,etc.It is suitable for the frost damage remediation project of high-speed railroad tunnel in the seasonal freezing area with high requirements for tunnel safety.The numerical simulation study shows that when the cold air of-20℃ continues to pass into the tunnel cavity for 90 days,the insulation effect of the tunnel paste-wall polyurethane insulation layer is89.90%～96.43%,and the insulation effect of off-wall corrugated steel plate insulation lining is 101.94%～107.14%.Therefore,the off-wall corrugated steel plate insulation lining has better insulation effect than the traditional methods and can eliminate the occurrence of frost damage probably and better cope with the adverse effects of long duration low temperature on the seasonal frozen area.The research results provide theoretical reference for the design of insulation and frost protection for similar projects. |
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