Abstract：It has become a common understanding that the structure，physico-mechanical properties of soils could be considerably changed by freezing-thawing cycles. With the variation of engineering properties，the normal running train was disturbed by the decline of subgrade stabilization. In order to study the long-term stabilization of slope in frozen soil area of Qinghai—Tibet Railway，a test was conducted under repeatedly freezing-thawing cycles，aiming at the main physico-mechanical properties of the representative clay. The results show that the physico-mechanical characters of the investigated soils become stable after 10 freezing-thawing cycles，such as water content，density，cohesion，internal friction angle and so on. The stable state is dependent on the original state of the soil sample，and the influence of the original dry density is very important. With the repeatedly freezing-thawing cycles，the cohesion of low density clay increases，but the cohesion of high density clay decreases，and the internal friction angle of the clay changes little. It is suggested that the parameters of soil at stable state should be adopted to estimate the stabilization of slope in frozen soil area.
