Under the condition of freeze-thaw cycles, two types of rock (granite and andesite), which were used as slope protection of the Qinghai-Tibet Railway, were tested according to the special climatic conditions in the Tibetan Plateau, and their various damage processes in appearance were carefully observed. The observation results show that the damage of andesite was more serious than that of the granite. Using acoustic instrument, ultrasonic velocity was tested. The changing trends of the velocity with cycle number of freeze-thaw were analyzed, and the freeze-thaw cycle damaging the physical and mechanical properties of rocks can be seen. According to the changing trends of the ultrasonic velocity with the cycle number of freeze-thaw, a few mechanical parameters of the rocks, such as dynamic elastic modulus, Poisson ratio, and dynamic bulk modulus, were analyzed. It is found that they all have declining trend as the cycle number of freeze-thaw increases, and in particular, when the cycle number reaches a certain extent, the Poisson ratio of part rocks begins to become negative.

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