| With the gradual improvement of the country’s economic strength,the country is gradually increasing the economic construction in the central and western regions and the qinghai-tibet plateau and other high-latitude regions.The premise for the rapid and steady progress of economic construction is the improvement of infrastructure.Accordingly,the "sichuan-tibet railway" and other major projects have been proposed.In order to shorten the length of roads and reduce economic input,the construction of tunnels is a two-sided solution,which leads to the increasing construction of tunnels in cold regions.Cold regions tunnel to more general areas are more likely to happen freezing damage,the frost heave and thawing settlement,this is because the temperature of surrounding rock are more easily affected by atmosphere temperature,sometimes in the temperature is sometimes a negative temperature,and moisture migration occurred under the effect of temperature gradient,which often make the tunnel lining structure appear crack,flake,ice,water,ice and other disasters.In particular,the buried depth of the tunnel is an important factor that directly affects the distribution of the temperature field and water field around the surrounding rock,and will directly lead to the long-term stability of the tunnel and an important indicator of the influence of the active surface layer on the freezing-thawing ring of the tunnel.Therefore,this paper explores the influence of construction season,moisture content and annual average temperature on the melting zone of tunnel caused by active surface layer under different burial depth conditions and designs a freeze-thaw model test of tunnel in cold zone.Through a series of working conditions,the influence of surface active layer on tunnel melt zone is summarized.Finally,through numerical simulation of COMSOL,PDE hydrothermal coupling programming is carried out to summarize the change law of surface active layer and tunnel melting ring in shallow section of wind-volcano tunnel excavation and how water changes,and to provide some Suggestions for tunnel excavation in cold region.In conclusion,the following rules can be obtained from the laboratory model test and numerical simulation:1.It can be seen from the buried depth of 30,20 and 10 cm that: as the buried depth decreases,the influence of surface active layer on tunnel freezing-thawing ring is gradually increasing until the influence of surface active layer on tunnel vault freezing-thawing ring overlapped,and the penetration is achieved;2.When the buried depth is 30cm: when the water content is 25% and 20%,the annual average temperature is-2 ° c and 0 ° c,and the construction season starts from 0 ° c to the maximum positive temperature or 0 ° c to the maximum negative temperature,it is impossible to penetrate the surface active layer and the tunnel vault freezing-thawing ring.The influence of the surface active layer on the tunnel freezing-thawing ring is limited or even negligible;3.When the buried depth is 20 cm,the moisture content is 25%,the construction season starts from 0℃ to the maximum positive temperature,and the annual average temperature is-2℃ and 0℃.The active surface layer has the greatest influence on the freeze-thaw circle of the tunnel,and it reaches its connection from the vault to the ground;4.When the burial depth is 10cm: under any condition,the surface active layer and the tunnel freezing-thawing ring can be penetrated through,and with the burial depth gradually shallower,the melting depth at the tunnel arch waist and invert position also increases gradually.The influence of the surface active layer on the tunnel freezing-thawing ring is affected by water content,annual average temperature and construction season;5.Under different burial depth conditions: the condition of influence degree of surface active layer on freezing-thawing ring of tunnel is the annual average temperature >construction season > moisture content;6.The water distribution between the surface and the tunnel is significantly shifted to the two sides due to the increase of the number of freezing-thawing cycles;7.According to the laws of the test to get to the wind after the volcano shallow buried tunnel construction stage excavation of duan hydrothermal coupling analysis found that the depth of the tunnel vault freeze-thaw circle as the surface layer increases,if after excavation supporting and reduce tunnel construction stage heat source in a timely manner,within 30 days in the same depth of freezing and thawing around the tunnel can reduce 10%,freeze-thaw circle delay 7 days.After a freeze-thaw cycle,the water content of surrounding rock after lining changes greatly,which has a great influence on lining safety. |
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