Mechanism Of Frost Heave And Thaw Settlement Of Subgrade And Stability Evaluation Of Subgrade In Alpine Permafrost Regions

The stability of the road depends on the stability of the roadbed,and the engineering properties of the permafrost directly affect the stability of the alpine permafrost,while the moisture and temperature have a direct impact on the stability of the subgrade.Based on the G219(Xinjiang)section,this paper analyzed the types of roadbed diseases in alpine permafrost by collecting and summarizing data.The indoor experiment was used to analyze the influence of water and temperature on frost heave and sink.Based on the field data of the special embankment in the permafrost region,the variation characteristics of the temperature,humidity and deformation of the embankment in the alpine permafrost region were analyzed.Based on the analytic hierarchy process,fuzzy comprehensive evaluation of roadbed stability was made from three aspects: natural environment factor,design factor and permafrost factor.And this paper achieved the following results:1)The natural environment and the types of roadbed diseases in G219 highway(Xinjiang)were investigated by field investigation and data collection.It is concluded that frost heave and thaw settlement are the main types of subgrade diseases in alpine permafrost regions.2)The changes of water,temperature and deformation during the process of frost heaving and thawing were analyzed by the method of indoor soil test to monitor the temperature,water and deformation of soil during frost heaving and melting.The freezing process can be divided into quick frost stage,transition frost stage and stable frost stage.And the frost heave deformation is divided into three stages: the frost heave deformation stage,the rapid development stage of frost heave deformation and the stabilization stage of frost heave deformation.The melting deformation is divided into Rapid deformation stage,slow deformation stage and stable stage.After a freeze-thaw cycle,the soil porosity increases and the soil deformation increases.3)Based on the G219 line,water,temperature and deformation sensors were embedded in four different subgrade forms of typical frozen ground sections,namely ordinary roadbe,the stone roadbed,the thermal embankment and the ventilation pipe subgrade.And the variation characteristics of water field,temperature field and deformation field were analyzed.4)In this paper,the causative factors of G219 subgrade disease were analyzed from the aspects of natural environment,design factors and permafrost factors.And the fuzzy comprehensive evaluation system of the roadbed risk degree in Xinjiang Alpine permafrost region was raised.Based on AHP and fuzzy comprehensive evaluation method,considered the actual situation of the Xinjiang Tibet highway,the fuzzy comprehensive evaluation model of the roadbed stability in the alpine permafrost region was established and the correctness of the model was verified.