Study On The Unstable Deformation Of Highway Subgrade In Permafrost Region

Permafrost in Qinghai-Tibet plateau takes up about sixty percent of the total area of permafrost in China, about 550 kilometers of the Qinghai-Tibet highway built on the Qinghai-Tibet plateau is located in the permafrost region with extremely severe environmental conditions. The Qinghai-Tibet highway was opened to traffic since 1954, the deformation of permafrost subgrade has occurred constantly and is uneven and different in different subgrade sections, and the maintenance work of the permafrost subgrade deformation has been performed in the process of operation. This paper takes the permafrost subgrade of Qinghai-Tibet highway as the research object, and studies the long-term deformation characteristics of permafrost subgrade conmbined with the distribution changes of permafrost subgrade temperature field and moisture field and traffic loads.1. According to the field investigation data analysis, the deformation of permafrost subgrade is uneven and has been occurred as the change of time and space. This paper defines the deformation as the unstable deformation, and then analyzes the causes and affecting factors of the unstable deformation of permafrost subgrade.2. In permafrost region, subgrade internal occurs phase transition with the cycle change of seasons. According to the control equation with phase change of the unsteady temperature field, with the boundary conditions of atmosphere temperature、solar radiation and surface effective radiation, this paper establishes subgrade temperature field finite element model, and then analyzes the long-term changes of subgrade temperature field distribution in permafrost region.3. Rainfall is one of the important sources of moisture in permafrost subgrade.According to the control equation of the moisture migration, on the basis of atmospheric rainfall and evaporation, this paper establishes the subgrade moisture field finite element model, and then analyzes the long-term changes of subgrade moisture field distribution in permafrost region.4. Based on the results of the temperature field and moisture field, this paper establishes the subgrade deformation field finite element model during freezing season and thawed season respectively, and then analyzes the long-term unstable deformation characteristics ofpermafrost subgrade.This article’s results reveals the long-term change laws of temperature field, moisture field and unstable deformation field of permafrost subgrade, these results can provide the references for the diseases control of Qinghai-Tibet highway in the future, and also can provide the reference frames for the construction of the Qinghai-Tibet expressway.