Liu Yong-zhi

Ground temperature monitoring and its recent change in Qinghai-Tibet Plateau

Abstract It is very important to analyze the change of the active layer and the permafrost thermal regime for Qinghai–Tibet Plateau. Formerly, there is only few data of monitoring to analyze the response of the active layer and the permafrost to climate change in Qinghai–Tibet Plateau. The monitoring data of the permafrost thermal regime with seven sites from 1995 to 2000 make it possible to analyze this response relationship. The monitoring data is used to analyze the recent change in the thickness of active layer, the subsurface temperature, the near permafrost surface temperature, and the permafrost temperature at the depth of 6 or 8 m. The results show that their changes have a better accordance with air temperature change. The climate change has an impact on the change of the active layer and the thermal regime of the permafrost. The change of the active layer and the thermal regime of the permafrost can indirectly explain some features of climate change.

Thermal regime in the embankment of Qinghai–Tibetan Highway in permafrost regions

Abstract Based on the data of two groups of ground temperature along Qinghai–Tibetan Highway in permafrost regions in recent five years, this paper analyzes the thermal regime in the embankment in higher and lower temperature permafrost regions, respectively. The results show that the annual mean ground temperature in the embankment is evidently higher than that in the natural ground and the thawing period in the embankment is longer than that in the natural ground, too. In the embankment of higher temperature permafrost regions, talik has formed between the active layer and below permafrost, and the heat flux entering the active layer is in an accumulative state. In both higher and lower temperature permafrost regions, the input of heat into the permafrost below the embankment is greater than the output. The causes of the continual thaw of permafrost in higher temperature permafrost regions are attributed to the ground temperature near 0 °C and the continuous accumulation of heat in the embankment. In lower temperature permafrost regions, the heat entering the permafrost below embankment is mainly to raise the temperature of permafrost for the moment. With the rise of ground temperature, the permafrost below embankment in lower temperature permafrost regions may also be thawed violently.

Interaction study of permafrost and highway along Qinghai-Xizang Highway

Eight monitoring sites are set along the Qinghai-Xizang Highway (QXH) to investigate the characteristics and process of interaction between permafrost and highway, including the upper and down boundaries of active layer under natural surface, seasonally freezing-thawing depth under asphalt pavement, permafrost table temperature and roadbed stability. The investigation results show that the changes of active layer thickness and permafrost table temperature under asphalt pavement are greater than these under natural surface due to the absorbing heat action and less evaporation of asphalt pavement, as a result, the engineering geological problems such as thaw settlement and frost heave present frequently along QXH line and produce the adverse impact on roadbed stability.

Cooling mechanism of embankment with block stone interlayer in Qinghai-Tibet railway

In order to study the cooling mechanism of embankment with block stone interlayer under open and closed conditions, an experimental railway section was built and data within one freeze-thaw cycle were collected. The results explain well the cooling mechanism of embankment with block stone interlayer. Under the open condition in cold seasons, the enforced convection effect occurs within block stone interlayer when the wind speed is large; however, the weak air convection occurs within the block stone interlayer near the bottom of the embankment when the wind speed is slow. Under the open condition in warm seasons, heat conduction occurs within block stone interlayer due to the change in wind speed and direction. Under the closed condition, however, the enforced convection within block stone interlayer is so weak that heat conduction is dominant in the whole year because wind is blocked. Therefore, the cooling effect of embankment with a block stone interlayer to the soil beneath it is produced by enforced convection and weak free air convection; both its process and the cooling intensity are controlled by the local wind speed and direction. Because of the difference in the cooling effects, the soil temperature beneath the embankment has a temperature difference of 2°C–4°C between the open and closed conditions.