| Permafrost area of Qinghai-Tibet Platean is 1. 5x106 km2,70 percent of permafrost area in China. On the basis of global warming, there is a degradation tendency for permafrost. The degradation tendency of permafrost will become worse caused by all kinds of human engineering activities. Geological hazards from freeze-thaw action will not only threat linear engineering construction for example, highway, railway, bridge, oil pipeline, etc et, but result in deterioration for ecological environment of cold region to lose recovery ability for permafrost. Thermal-thaw sliding collapse is a typical example.The following researches have been carried out in this paper, including slope instability patterns analysis in permafrost region of Qinghai-Tibet Platean, geological structure analysis for typical permafrost slope, model experiment of thermal-thaw sliding collapse of Qinghai-Tibet milestone K3035, stability analysis method, in-situ monitoring and numerical simulation of temperature field, displacement field. The following conclusions have been put forward.(1)On the basis of concluding research results of permafrost slope along Qinghai-Tibet highway, permafrost instability patterns are divided into two categories, freezing soil sliding and thawing soil sliding.Gelifluction & thaw slumping are concluded in thawing soil sliding. Creep sliding & collapse sliding are concluded in freezing soil sliding, It is precondition that soils are saturated by water and thick ice takes as sliding face for gelifluction and thaw slumping.(2)Factors caused by thaw slumping are as follows, a. thick layer ground ice and shallow embedding depth, b. thick layer ground ice uncovered(3)Thaw slumping in milestone K3035 of Qinghai-Tibet highway is not sliding at a time. At present, movement of slope scale begin with melting, crack, collapse. During positive temperature every year, sliding collapse begin to develop with depth in 2m,between July and October, in the period of 3 years between 2000 and 2002 ,it is estimated velocity of thaw slumping is 5m/a.(4)Water conditions are important for any slop sliding. It show that during thaw season, for collapse sliding of milestone K3035 of Qinghai-Tibet highway , water content of soil above 2m in depth is more than 30%, it is higher than liquid limit value situated on thick layer ice. Water content is more than 19% for collapse sliding of milestone K3057 of Qinghai-Tibet highway. At the same time, water content of no sliding soil is less than 18%, water content of sliding soil is obviously higher than that of no sliding soil. Water Congregation at ice surface is mainly caused by ground ice melting. It is melting water that soil strength is obviously decrease, and sliding along thick ice surface. 〢ccording to the first law of simulation theory, simulation index and criterion for permafrost slope model have be concluded and built by applying integration comparison method. It is concluded that taking in-situ soil as similar material, six similar parameters willbe decreased two parameters, this is ct and cl .Time scale factor between prototype andscale model is determined by geometry scale factor, this is ,ct =cl2 . Only one similar factoris self-variable, another is dependency variable. The following conclusions have been concluded, deformation field is controlled by temperature field. During a series of temperature cycles, there are critical temperature value successive displacement. Frost heaving and thaw settlement for slope soil surface are calculated and analyzed by applying self-design model triangle frame. It is concluded that frost heaving is much more than thaw settlement, it is in accordance with observation results along Qinghai-Tibet highway.(6)Differential equation of heat transfer with phase change is derived in this paper. Simulation of temperature displacement field of permafrost slope at milestone K3035 of Qinghai-Tibet highway have been carried out by Marc finite element software. Displacement of 5 years is simulated behind sliding step. It is drawn out that displacemen...
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