| Because of long-term operation,many problems,such as subsidence,cracks and embracing,often occur on roads built in frozen areas,which poses great challenges to road maintenance and repair,and also brings certain environmental impact.With the development of Western China,the Qinghai-Tibet Expressway has been incorporated into the National Expressway network.The length of the section from Golmud to Lhasa is 1100 kilometers,and it is planned to be built on the Qinghai-Tibet Plateau at an average altitude of more than 4000 meters.The passage through permafrost and seasonal frozen soil areas will have a significant impact on the original environmental conditions,which may lead to changes in the original ecological ice distribution,the decline of some soil,or the rise of buildings built on the soil caused by frost heave.The existing research results mainly focus on the simulation of the temperature field of low-grade highway,while the applicability of the temperature field of high-grade highway needs to be explored.Based on the theory of heat conduction and water transfer,the coefficient-type partial differential equation with Comsol software is used to compile the corresponding parameters twice.Based on the Highway Engineering Technology Standard and the Detailed Rules of Highway Design and Construction Technology in Permafrost Regions,the model of separated and integral roadbed section is established,and the consideration of water transfer and non-consideration of water are explored.The influence of different migration on Subgrade temperature is different.The influence of pavement width,slope and subgrade height on temperature distribution is analyzed.The results can provide a theoretical basis for the construction of Expressway in this section.The main results are as follows:(1)Without considering water transfer,the width of subgrade increases from12.75 m to 13.75 M.The maximum melting depth of Subgrade in the first five years of simulation has little difference.In the next 15 years,the melting depth of subgrade with 13.75 m width is larger and faster than that of growth.When considering water transfer,the maximum melting depth fluctuation amplitude is smaller than thatwithout considering water transfer,and the corresponding time of maximum melting limit will be prolonged with the increase of pavement width.(2)Regardless of water migration,1/2 slope selection is better than 1/1.5 for the reduction of roadbed melting depth in the separate layout,while the effect of slope can not be ignored when considering water migration.In the integral layout,the width of roadbed is the main influential factor compared with the slope,and the simulation difference between 1/2 slope and 1/1.5 slope is not significant,and the slope has little influence on it.First,considering water migration,the influence of slope on roadbed melting depth is not negligible.To some extent,it can be neglected.(3)Compared with 3M and 4m high roadbed,the maximum melting depth of5 m high roadbed decreases,and the permafrost upper limit of roadbed rises significantly.Without considering water migration,3M of roadbed is 4m relative to roadbed.From the beginning of the simulation to the 15 th year,the maximum difference is about 0.5m,and then to the 20 th year,the difference gradually decreases.(4)The interaction between the "normal section" is preliminarily discussed.It is concluded that the selection of the boundary conditions of the "oblique section" can not be simply equivalent and needs further verification. |
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