Stability Analysis Of Subgrade Upon The Slope With Surface Pounding In Permafrost Region

Since rainfall intensity is large in summer along the Qinghai-Tibet railway, water accumulation is serious in the toe of some subgrade upon the slope, the safety of sloped subgrade in the permafrost zone becomes increasingly prominent. This paper is based on a subgrade upon the slope of Amdo the section of the Qinghai-Tibet Railway, By analyzing its meteorological and rainfall data,summing up the temperature and seepage boundary conditions of the sloped subgrade in the numerical simulation. Model subgrades upon four gradient (7°,9°,11°and13°) slopes by using GeoStudio2007, simulate the temperature field and stability of the sloped subgrades with or without surface pounding.The main contents and conclusions are as follows:(1) Compare the changes of the temperature field of four subgrades upon gradients (7°,9°,11°and13°) slopes, analysis the variation of the warm-season thawing depth of subgrade center, permafrost table and cold-season melting thickness. Study the impacts of slope gradient on the temperature field and thermal stability.(2) By comparing the temperature field of a same gradients slope with and without surface pounding, analysis the variation of the warm-season thawing depth of subgrade center, permafrost table and cold-season melting thickness vs time, Study the impacts of surface pounding on the temperature field and thermal stability.(3) Simulate the subgrades upon four kinds of gradient slope, compare the trends of safety factor vs time and gradient under different gradients subgrade. Study the impacts of gradient on the slope stability.(4) Compare the safety factor of the same gradient sloped subgrade vs time with and without surface pounding, study the impact of surface pounding on the stability of slope subgrade. By analyzing the calculated results, the slope gradient has a great effect on the stability of slope subgrade:As the slope gradient increasing in the permafrost region, water infiltration enhances, the warm-season thawing depth of subgrade center, permafrost table decline, while increasing the thickness and presence time of cold-season melting nuclear, Ultimately reduce the thermal stability of sloped subgrade, it do harm to the stability of the whole slope subgrade.As the same time surface pounding seriously affect the stability of subgrade:It increases the amplitude of permafrost table reduction and the thickness of the melting nuclear of subgrade in the winter, delay the winter refreezing time, reduce the thermal stability of the sloped subgrade; Finally, it makes the stability safety factor of the sloped subgrade decline, it do harm to the stability of the whole slope subgrade. we can summarize that the possibility of instability of subgrade upon the slope is the largest in the permafrost regions in the melting season, and subgrade stability increase rapidly in the freezing period.