Wu Qingbai

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.

The effect of climate warming on the Qinghai-Tibet Highway, China

Climate warming greatly affected the environment in the Qinghai-Tibet plateau. Climate warming has led to the degradation of permafrost along the Qinghai-Tibet Highway (QTH). In such regions, the additional absorptive heat of the asphalt pavement has led to serious deterioration of the road. At the same time, climate warming will increase the depth of the active layer and will increase thaw settlement. Response measures can mitigate further destruction of the QTH. Ground temperatures are used to define permafrost zones and the stability of permafrost. The probable change with climate warming is predicted.

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.

Calculation method for thickness of discontinuous boundary layer of engineering pavement

The boundary layer is a buffer layer of water and heat exchange between the atmosphere and permafrost. Based on the atmospheric boundary layer and heat transfer theory, we established a method for determining the boundary layer thickness of engineering pavement (asphalt and sand pavement) in permafrost region. The boundary layer can be divided into the Boundary Layer Above Surface (BLAS) and the Boundary Layer Below Surface (BLBS) . From in-situ monitoring data, the thickness of BLAS was determined through the laminar thickness, and the thickness of BLBS was determined through ground temperature, the heat conduction function, and the mean attenuation function ( α ) . For asphalt pavement, the BLAS thickness varied between 2.90 and 4.31 mm and that of BLBS varied between 28.00 and 45.38 cm. For sand pavement, the BLAS thickness varied between 2.55 and 3.29 mm and that of BLBS varied between 15.00 and 46.44 cm. The thickness varied with freezing and thawing processes. The boundary layer calculation method described in this paper can provide a relatively stable boundary for temperature field analysis.