Study On The Temperature Field Evolution Of Crushed Rock Subgrade In The Permafrost Regions

As the frozen soil is very sensitive to temperature changing, crushed rock subgrade is one of the effective measures and appropriate structures to reduce the influence of embankment and preserve underlying permafrost. The crushed rock subgrade can keep stability in permafrost regions. This paper has taken a series of research, such as laboratory test, field test and numerical simulation and so on.In order to obtain the useful data about engineering design and performance evaluation, we carried out and analyzed the laboratory tests. Based on the temperature field test data of the test engineering parallel to Qinghai-tibet highway, we analyzed the cooling effect of the crushed rock subgrade through the comparison between crushed rock subgrade and ordinary embankment. This paper starts from the principle of the crushed rock subgrade, the factors influenced to the temperature field are analyzed. Established a non-steady temperature field modeling companied by phase transition under the first boundary condition, according to the principle of boundary layer, presented the determination of the first boundary condition. The finite element model (FEM) of the crushed rock subgrade temperature field is established, the temperature fields of the crushed rock subgrade are simulated in different influencing factors such as the rubble grain size, thickness and position of rubble stratum. Subsequently, the influences of different factors to the crushed rock subgrade are analyzed in details. Combined with the results, the design principle has been proposed.The analysis of simulation results shows that:the crushed rock subgrade can preserve the underlying permafrost better and remedy the permafrost change following the construction of embankment with years. Different rubble grain sizes can all preserve permafrost. In contrast, the appropriate range of rubble grain size is 6-8cm. Thicker the rubble stratum is, stabler the underlying permafrost is. As the temperature difference of two embankments near thickness become lessening with the thickening of rubble stratum, the minimum stratum thickness should be larger than 0.6m. The position of rubble stratum has a remarkable influence to the temperature of the crushed rock subgrade. As a higher position can lead to a stronger cooling effect, it should be more appropriate to put the stratum straight on the surface of the subgrade.