Niu Fujun

Acoustic experimental study of two types of rock from the Tibetan Plateau under the condition of freeze-thaw cycles

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.

Performance comparison of permafrost models in Wudaoliang Basin, Qinghai-Tibet Plateau, China

Knowledge of the spatial distribution of permafrost and the effects of climate on ground temperature are important for land use and infrastructure development on the Qinghai-Tibet Plateau (QTP). Different permafrost models have been developed to simulate the ground temperature and active layer thickness (ALT). In this study, Temperature at Top of Permafrost (TTOP) model, Kudryavtsev model and modified Stefan solution were evaluated against detailed field measurements at four distinct field sites in the Wudaoliang Basin to better understand the applicability of permafrost models. Field data from 2012 to 2014 showed that there were notable differences in observed ground temperatures and ALTs within and among the sites. The TTOP model is relatively simple, however, when driven by averaged input values, it produced more accurate permafrost surface temperature (Tps) than the Kudryavtsev model. The modified Stefan solution resulted in a satisfactory accuracy of 90%, which was better than the Kudryavtsev model for estimating ALTs. The modified Stefan solution had the potential of being applied to climate-change studies in the future.Furthermore, additional field investigations over longer periods focusing on hydrology, which has significant influence on permafrost thaw, are necessary. These efforts should employ advanced measurement techniques to obtain adequate and extensive local parameters that will help improve model accuracy.