Shuangyang Li

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.

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...

Influence of Nanosilica on the Freezing and Thawing Characteristics of Sand, Silt and Silty Clay

This paper presents an experimental study aiming to understand the impacts of nanosilica on the freezing and thawing properties of soils. We use freezing and thawing processes to investigate the freezing point, supercooling temperature, thawing point and equilibrium freezing time of three types of soils (i.e., Delingha sand, Lanzhou silt and Beiluhe silty clay) under different nanosilica contents. The results show that the freezing point, supercooling temperature and melting point decrease with the increase of nanosilica content. The equilibrium freezing time decreases with increasing nanosilica content, however, the equilibrium freezing time remains constant when the nanosilica content exceeds 1.0%. In addition, SiO2 nanoparticles are able to act as nanofillers to recover the pore structure of the specimens by decreasing harmful pores. The research results could provide help for applications of nanomaterials in cold regions.

Heat balance integral method for the heat conduction problems with phase change

Heat conduction problems with phase change occur naturally in many physical and industrial processes. A moving boundary of these problems results in strong nonlinear. Very few analytical solutions to these problems are obtained. Numerical methods and approximate methods are two kinds of methods solving these problems. Heat Balance Integral Method (HBIM) is an approximate method to effectively solve these problems. There is not a systematic principle for the selection of an approximate solution profile in original HBIM, and the calculation accuracy is not as good as expected. This paper provides a general rule to select the approximate solution profile in HBIM. A new method for determining the parameters in approximate solution is proposed. The results show that the new method improves accuracy greatly.