The influence of cyclic loading on frozen soil may be reflected by the variation of soil temperature. To uncover this process, dynamic triaxial tests were performed in this study on saturated warm frozen soil, during which the temperature changes inside the specimens were monitored. The effects of initial dry density, test temperature, dynamic stress amplitude and vibration frequency on temperature change were studied. The results universally manifested a rise in specimen temperature under cyclic loading. The higher dynamic stress, vibration frequency, testing temperature and initial dry density was responsible for the faster heating rate. The mechanism controlling the temperature variation inside the specimens could be explained by the heat production as a result of friction and extrusion between soil grains when subjected to dynamic loading. This temperature rise could be compromised by the heat transfer with the thermal environment where the specimen was in. A colder environment would cause the specimen temperature to drop back. This study provides an experimental foundation for deeply understanding how the mechanical behavior of frozen soil degrades under dynamic loading.

Understanding temperature variability especially elevation dependent warming (EDW) in high-elevation mountain regions is critical for assessing the impacts of climate change on water resources including glacier melt, degradation of soils, and active layer thickness. EDW means that temperature is warming faster with the increase of altitude. In this study, we used observed temperature data during 1979-2017 from 23 meteorological stations in the Qilian Mountains (QLM) to analyze temperature trend with Mann-Kendall (MK) test and Sen's slope approach. Results showed that the warming trends for the annual temperature followed the order of T_min > T_mean > T_max and with a shift both occurred in 1997. Spring and summer temperature have a higher increasing trend than that in autumn and winter. T_mean shifts occurred in 1996 for spring and summer, in 1997 for autumn and winter. T_max shifts occurred in 1997 for spring and 1996 for summer. T_min shifts occurred in 1997 for spring, summer and winter as well as in 1999 for autumn. Annual mean diurnal temperature range (DTR) shows a significant decreasing trend (-0.18 degrees C/10a) from 1979 to 2017. Summer mean DTR shows a significant decreasing trend (-0.26 degrees C/10a) from 1979 to 2017 with a shift occurred in 2010. After removing longitude and latitude factors, we can learn that the warming enhancement rate of average annual temperature is 0.0673 degrees C/km/10a, indicating that the temperature warming trend is accelerating with the continuous increase of altitude. The increase rate of elevation temperature is 0.0371 degrees C/km/10a in spring, 0.0457 degrees C/km/10a in summer, 0.0707 degrees C/km/10a in autumn, and 0.0606 degrees C/km/10a in winter, which indicates that there is a clear EDW in the QLM. The main causes of warming in the Qilian Mountains are human activities, cloudiness, ice-snow feedback and El Nino phenomenon.