Wansheng Pei

The coupled moisture‐heat process of permafrost around a thermokarst pond in Qinghai‐Tibet Plateau under global warming

Due to environmental disturbances such as local human activity and global warming, melting of massive ground ice has resulted in thermokarst ponds, which are extensively distributed in the Qinghai-Tibet Plateau (QTP). Besides the global warming, the thermokarst pond, as a major heat source, speeds up the moisture change and degradation of its surrounding permafrost. To analyze the long-term coupled moisture-heat process near a representative nonpenetrative thermokarst pond in a permafrost region, abundant temperature data over multiple years at different depths and horizontal distances from the center of the thermokarst pond have been collected at a field experimental station in QTP. A numerical model is built to analyze this thermokarst pond. The temperature and moisture processes of surrounding permafrost are simulated by this model and compared with measured temperature data. Our results show that if the rate of air temperature rise is 0.048 degrees C/yr, which refers to a 2.4 degrees C temperature rise over 50years, the thawing fronts underneath the thermokarst pond move downward at a linear rate of 0.18m/yr and the permafrost beneath the pond center would disappear after the year of 2281. Beyond that time, the impact range of the pond on the natural ground increases to about 50m in horizontal direction. So a dish-shape thawing zone occurs around the thermokarst pond. Simultaneously, the moisture state is greatly changed in 2281 and becomes completely different from that in 2013. All of these would inevitably deteriorate the ecological and environmental system in QTP.

Moisture–temperature changes and freeze–thaw hazards on a canal in seasonally frozen regions

Freeze–thaw action is a complex moisture–heat-mechanics interaction process, which has caused prevailing and severe damages to canals in seasonally frozen regions. Up to now, the detailed frost damage mechanism has not been well disclosed. To explore the freeze–thaw damage mechanism of the canal in cold regions, a numerical moisture–heat-mechanics model is established and corresponding computer program is written. Then, a representative canal in the northeast of China is taken as an example to simulate the freeze–thaw damage process. Meanwhile, the robustness of the numerical model and program is tested by some in situ data. Lastly, the numerical results show that there are dramatic water migration and redistribution in the seasonal freeze–thaw variation layer, causing repetitive frost heave and thaw settlement, and tension–compression stresses. Therefore, the strengths of soil are reduced after several freeze–thaw cycles. Further, the heavy denudation damage and downslope movement of the canal slope would be quite likely triggered in seasonally frozen regions. These zones should be monitored closely to ensure safe operation. As a preliminary study, the numerical model and results in this paper may be a reference for design, maintenance, and research on other canals in seasonally frozen regions.

Lateral thermal disturbance of embankments in the permafrost regions of the Qinghai-Tibet Engineering Corridor

Numerous engineering projects have been completed on the Qinghai-Tibet Plateau, and with continued economic growth, additional important engineering projects are being planned. Major transportation construction is largely restricted to the Qinghai-Tibet Engineering Corridor, which is as narrow as a few hundred meters in some places. In this narrow corridor, projects such as the Qinghai-Tibet Railway and the Qinghai-Tibet Highway can influence the stability of the permafrost. We use a numerical model to investigate the individual thermal disturbance caused by the Qinghai-Tibet Railway, the Qinghai-Tibet Highway, and the planned Qinghai-Tibet Expressway. To simulate an upper limit of disturbance under current climate we use the most unfavorable combination of engineering design practices, with unprotected embankments, a traditional ballast embankment for the Qinghai-Tibet Railway, and traditional asphalt pavement embankments for the Qinghai-Tibet Highway and the Qinghai-Tibet Expressway. The lateral thermal disturbance extent of the three projects increases linearly with embankment height. Under the same embankment heights, the lateral extent of thermal disturbance is smallest for the Qinghai-Tibet Railway and is largest for the full Qinghai-Tibet Expressway. The model results provide guidance for minimum distances between the transportation projects to prevent thermal interaction, as a function of embankment height and design. In future research it is important to evaluate the thermal disturbance scopes of other engineering structures, such as tunnels, bridges, and oil pipelines, and to evaluate the thermal interaction and cumulative impact of multiple structures under current and future climate scenarios.

Effect of Inclination Angle on the Heat Transfer Performance of a Two-Phase Closed Thermosyphon under Low-Temperature Conditions

AbstractIn this study, a series of laboratory investigations were performed to examine the heat transfer performance of a two-phase closed thermosyphon (TPCT) with different inclination angles under low-temperature conditions. A stainless steel TPCT with ammonia as the working fluid was tested with inclination angles ranging from 0 to 90° from the horizontal. In order to simulate low-temperature conditions, the temperature in the jacket of evaporator section was controlled at −0.5°C, and the temperature in the jacket of the condenser section was changed from −0.7 to −15.0°C. The experimental results show that inclination angle has a significant impact on the heat transfer performance of a TPCT under the experimental conditions, but the inclination angle does not control the startup temperature difference for the TPCT when the inclination angle is more than 0°. A horizontal TPCT has a good heat transfer performance and a small startup temperature difference; however, the thermal semiconduction effect disap...

Effect of Temperature Gradients on the Frost Heave of a Saturated Silty Clay with a Water Supply

AbstractFrost heave is the primary cause of frost damage in cold regions. For frost-susceptible soils, water migration induced by a temperature gradient is a key factor in determining the frost hea...

Water–heat migration and frost-heave behavior of a saturated silty clay with a water supply

ABSTRACT In this study, a large-scale one-directional freezing experiment with water supply was performed to investigate the water–heat migration and frost-heave behavior of the saturated silty clay. The results indicate that the temperature gradient is larger in the frozen zone than that in the unfrozen zone because of the heat release of the supplied water and its water–ice phase change during the freezing process. Furthermore, the different parts of the total frost heave are evaluated, respectively, and it is also found that the frost heave can be reduced if the advance rate of the freezing front is effectively controlled even if external water is sufficient.

Cooling Performance of a Composite Embankment for High-Grade Highways in Permafrost Regions

In permafrost regions, high-grade highways with a wide and dark-colored asphalt pavement can cause the degradation of underlying permafrost. However, the embankments with single commonly cooling technique, e.g. two-phase closed thermosyphon (TPCT) embankment and crushed-rock embankment cannot effectively solve the problem. Therefore, a composite embankment for high-grade highways, combined with L-shaped TPCTs, crushed-rock revetments and insulation was designed. The L-shaped TPCTs were used to cool the core of the embankment, the crushed-rock revetments with different thicknesses was intended to cool the side slopes and to diminish the sunny-shady slope effect, and the insulation was designed to strengthen the cooling effect by increasing the thermal resistance of the embankment. Here, we experimentally and numerically evaluated the cooling performance of the composite embankment. The results indicate that the composite embankment can effectively raise the permafrost Table (0 °C isotherm) and cool the underlying permafrost under a separated high-grade highway with a wide and dark-colored asphalt pavement (double lanes each direction). Therefore, the composite embankment structure should be considered to be applied to the construction of high-grade highways in permafrost regions.