Evolution Law And Control Method Of Subgrade Thaw-Settling Along Mohe-Beijicun Highway

The northeast permafrost region is the second largest distribution area of permafrost in China,and the distribution of permafrost in this region has obvious latitudinal difference.Mohe-Beijicun highway in Daxing'anling area is the first high-grade highway of high continuous permafrost areas in China.According to the investigation,the subgrade disease of Mohe-Beijicun highway such as collapse,waves deformation,uneven settlement and slope sliding is happened under the influence of the global climate warming and human engineering activities.Based on the fact of permafrost degradation in Daxing'anling area and focused on the needs of subgrade maintenance of Mohe-Beijicun highway,the purpose of this paper is to explore the evolution law and control method of subgrade thaw-settling along MoheBeijicun highway.By means of field monitoring and numerical simulation,the evolution law of subgrade thermal field and deformation field within 50 years after the construction of Mohe-Beijicun highway is studied,and a suitable control method of subgrade thawsettling is proposed.The main research contents and conclusions are as follows:(1)After investigation,the main sections of Mohe-Beijicun highway where the thawsettling disease occurred were determined.The temperature and deformation sensors are embedded in the field,and the remote monitoring of thermal field and deformation field of the subgrade of Mohe-Beijicun highway is realized.The distribution characteristics and variation rules of the thermal field of the subgrade during the monitoring period are obtained through the data collection and analysis.(2)Based on the COMSOL Multiphysics finite element analysis software,the thermal-mechanical coupling numerical model of Mohe-Beijicun highway was established,and it was found that the thermal field of natural foundation and subgrade were in the mutual equilibrium stage within 5 years after the subgrade was built,and then the influence of external air-warming on soil thermal field began to appear.The construction of subgrade destroys the uniformity of thermal field of the original foundation and makes the continuous permafrost in the foundation become discontinuous island permafrost gradually.The development of subgrade settlement tends to be first fast and then slow.The settlement at the center line of subgrade is the largest,which mainly occurs in the clay layer with high temperature and high ice content in the foundation.(3)Based on the research of the original subgrade thermal field and deformation field,the numerical model of thermosyphon subgrade of Mohe-Beijicun highway is established,and the influence of thermosyphon on thermal field and deformation field of permafrost subgrade is studied.The influence of the horizontal arrangement position,embedding depth and shape of thermosyphon on the subgrade thermal field and deformation field is analyzed,then propose that L-type thermosyphon should be buried at the foot of subgrade slope.