scholarly journals A New Mitigation Measure to Counter Thermal Instability of Air-Cooled Embankment in Sandy Permafrost Zones of Tibet Plateau

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Minghao Liu ◽  
Jing Luo ◽  
Liang Zhang ◽  
Xin Ju
Keyword(s):  
Cooling Capacity ◽  
Ground Temperature ◽  
Tibet Plateau ◽  
Crushed Rock ◽  
Transfer Model ◽  
Rock Layer ◽  
Cooling Performance ◽  
Permafrost Warming ◽  
Warm Permafrost

A crushed-rock revetment (CRR) with high permeability that can be paved on embankment slopes is widely used to cool and protect the subgrade permafrost. In this study, a traditional CRR over warm permafrost was selected to investigate its cooling characteristics based on the ground temperature observed from 2003 to 2014. A new mitigation structure (NMS) was designed to improve the cooling capacity of the CRR and to counter the pore-filling of the rock layer. Numerical simulations were conducted to evaluate the cooling performance and reinforcing capacity of the NMS based on a developed heat and mass transfer model. The results indicate that the traditional CRR can improve the symmetry of the permafrost subgrade and decrease the ground temperature of shallow permafrost. However, the CRR cannot generate strong enough cooling to influence the deep (below 10 m depth) and warm permafrost with a mean annual ground temperature above −1.0°C. The wind-blown sand can further weaken the cooling of the CRR and cause significant permafrost warming and thawing beneath the slopes, posing a severe threat to the long-term safe operation of the embankment. The proposed NMS can produce a significantly superior cooling performance to the CRR. If the CRR is reinforced by the new structure, it can not only effectively cool the underlying warm permafrost but also elevate the permafrost table. The new structure can also protect the rock layer on the slopes from sand-filling. The NMS can be used as an effective method for roadbed design or maintenance over warm permafrost.

scholarly journals Analysis on Cooling Effect of Crushed-Rocks Embankment of Qinghai-Tibet High-Grade Road

2015 ◽  
Vol 2015 ◽  
pp. 1-8
Author(s):  
Dongqing Li ◽  
Kun Zhang ◽  
Gangqiang Tong ◽  
Feng Ming ◽  
Xing Huang
Keyword(s):  
Wind Tunnel Test ◽  
Resistance Coefficient ◽  
Cooling Effect ◽  
Tibet Plateau ◽  
Crushed Rock ◽  
High Grade ◽  
Calculation Results ◽  
Cooling Effects ◽  
Qinghai Tibet Plateau

In order to study the cooling effect of the crushed-rocks embankment, the permeability and the inertial resistance coefficient were measured by the wind tunnel test of spheres with a diameter of 20 cm, and then the stabilities of the closed crushed-rocks embankment with the wide pavement, the closed crushed-rocks embankment with the narrow pavement, and the duct-ventilated and closed crushed-rocks embankment were calculated. In the next 50 years, assuming that the temperature in Qinghai-Tibet plateau will rise by 2.6°C condition, the cooling effects of these three special high-grade embankment structures were studied. The test results and the numerical calculation results show that the relationship between pressure gradient and seepage velocity in the spheres layer diverges completely from Darcy’s law, and it shows a nice quadratic nonlinear relationship. Stabilities of those two closed crushed-rock embankments without the duct-ventilated structure could be destroyed because of the high permafrost temperature under embankments. The duct-ventilated and closed crushed-rocks embankment can cool down the permafrost effectively and raise the permafrost table and ensure the long-term thermal stability of permafrost under road.

scholarly journals Permafrost, active layer and meteorological data (2010–2020) from a relict permafrost site at Mahan Mountain, Northeast of Qinghai-Tibet Plateau

2021 ◽  
Author(s):  
Tonghua Wu ◽  
Changwei Xie ◽  
Xiaofan Zhu ◽  
Jie Chen ◽  
Wu Wang ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Active Layer ◽  
Thermal State ◽  
Meteorological Data ◽  
Water Vapor Pressure ◽  
Ground Temperature ◽  
Tibet Plateau ◽  
Different Depths ◽  
Qinghai Tibet Plateau

Abstract. Relict permafrost presents an ideal opportunity to understand the impacts of climatic warming on the ground thermal regime since it is characterized by mean annual ground temperature close to 0 °C and relatively thin permafrost. The long-term and continuous observations of permafrost thermal state and climate background are of great importance to reveal the links between the energy balance on hourly to annual timescales, to evaluate the variations of permafrost thermal state over multi-annual periods and to validate the remote sensing dataset. Until now there are few data available in relict permafrost regions although those data are important to understand the impacts of climate changes on permafrost especially in the boundary regions between permafrost and seasonally frozen ground regions. In this study, we present 11 years of meteorological and soil data in a relict permafrost site of the Mahan Mountain on the northeast of the Qinghai-Tibet Plateau. The meteorological data are comprised of air and ground surface temperature, relative humidity, wind speed and direction, shortwave and longwave downward and upward radiation, water vapor pressure, and precipitation on half-an-hour timescale. The active layer data include daily soil temperature and soil moisture at five different depths. The permafrost data consist of ground temperature at twenty different depths up to 28.4 m. The high-quality and long-term datasets are expected to serve as accurate forcing data in land surface models and evaluate remote-sensing products for a broader geoscientific community. The datasets are available from the National Tibetan Plateau/Third Pole Environment Data Center (https://doi.org/10.11888/Cryos.tpdc.271838, Wu and Xie, 2021).

scholarly journals Changes in Ground Temperature and Dynamics in Mountain Permafrost in the Swiss Alps

2021 ◽  
Vol 9 ◽  
Author(s):  
Anna Haberkorn ◽  
Robert Kenner ◽  
Jeannette Noetzli ◽  
Marcia Phillips
Keyword(s):  
Ground Temperature ◽  
Swiss Alps ◽  
Permafrost Degradation ◽  
Rock Glacier ◽  
Borehole Data ◽  
Ground Temperatures ◽  
Air Temperatures ◽  
Mountain Permafrost ◽  
Permafrost Warming

Rising air temperatures and increasingly intense precipitation are being observed in the Swiss Alps. These changes strongly affect the evolution of the temperature regime and the dynamics of mountain permafrost. Changes occur at different rates depending on ground ice content. Long-term monitoring reveals progressive warming and degradation of permafrost and accelerating rock glacier velocities. This study analyses changes occurring in ice-rich (excess-ice) and ice-poor mountain permafrost in Switzerland between 1997 and 2019 on the basis of ground temperature and rock glacier dynamics measurements carried out by the WSL Institute for Snow and Avalanche Research SLF at seven sites. Long-term borehole data indicate an increase of ground temperatures at all depths, in particular at ice-poor and nearly snow-free sites. Active layers are thickening at most sites and prolonged periods of active layer thaw are observed. Long autumn zero curtains are observed in ice-rich permafrost, possibly leading to an overall acceleration of rock glaciers. All these changes point towards ongoing permafrost warming and permafrost degradation in future.

The Application of Crushed Rock Materials upon Railway Embankments in Permafrost Regions

2011 ◽  
Vol 255-260 ◽  
pp. 4027-4033 ◽  
Author(s):  
Yan Hu Mu ◽  
Wei Ma ◽  
Zhi Zhong Sun ◽  
Yong Zhi Liu
Keyword(s):  
Thermal Stability ◽  
Warming Trend ◽  
Ground Temperature ◽  
Crushed Rock ◽  
Rock Materials ◽  
Ground Temperatures ◽  
Permafrost Table ◽  
Thermal Stability Of ◽  
Permafrost Regions

Crushed rock materials had been utilized extensively upon embankments, termed as crushed rock embankment (CRE), along the Qinghai-Tibet Railway in permafrost regions. Based on a long-term monitoring system along the railway, thermal stability and deformation characteristics and mechanisms of CRE were analyzed by field monitoring datasets from 2005 to 2009. The thermal stability analyses indicated that permafrost tables beneath CRE all had upwards movements but to varying degrees. For U-shaped crushed rock embankment (UCRE), the thermal stability of underlying permafrost kept well; along with permafrost table moving upwards, the shallow ground temperatures beneath the embankment decreased obviously while deep ground temperatures kept almost constant. For crushed rock revetment embankment (CCRE), the cooling effect was effective in cold permafrost regions. But in warm permafrost regions, the shallow permafrost beneath the embankment had no obvious cooling trend while the deep permafrost had a slight warming trend. The deformation analyses indicated that CREs experienced frost heave in permafrost regions with mean annual ground temperature (MAGT) < -1.5 °C but settlement in permafrost regions with mean annual ground temperature > -1.5 °C. The magnitudes of both heave and settlement were not significant. Since the better thermal stability of underlying permafrost, it was inferred that the settlement of CRE mainly originated from compression of warm and ice-rich permafrost layer near permafrost table.

scholarly journals Experimental and Numerical Analyses of the Thermal Regime of a Traditional Embankment in Permafrost Regions

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Qihang Mei ◽  
Ji Chen ◽  
Shouhong Zhang ◽  
Xin Hou ◽  
Jingyi Zhao ◽  
...  
Keyword(s):  
Climate Warming ◽  
Thermal Regime ◽  
Thermal Characteristics ◽  
Ground Temperature ◽  
Transfer Model ◽  
Thermal Disturbance ◽  
Undisturbed Site ◽  
Longitudinal Cracks ◽  
Permafrost Regions

Traditional embankment is widely used in the permafrost regions along the Qinghai-Tibet Railway (QTR) because of its simple construction and lower cost. However, this form of embankment has insufficient ability to resist external thermal disturbance. To clarify the thermal characteristics of traditional embankment under climate warming, the ground temperature change process of section K1068 + 750 of the QTR was analysed in this study. Based on the field monitoring data from 2006 to 2019 and the established heat transfer model, the past and future changes of permafrost thermal regime under the embankment were analysed. The results show that the degradation of permafrost under the embankment is faster than that under the undisturbed site due to the combined of embankment construction and climate warming. The sunny-shady slope effect related to embankment orientation makes the distribution of permafrost temperature under embankment asymmetric. In the long term, permafrost degrades both under the undisturbed site and embankment. The continuous degradation of permafrost causes the settlement and deformation of embankment, especially the asymmetric degradation of permafrost on sunny side and shady side will cause longitudinal cracks on the embankment. Therefore, timely application of strengthening measures which can slow down the degradation of permafrost and adjust the uneven ground temperature on the sunny and shady sides under the embankment is of great significance to the safety of the traditional embankment.

scholarly journals Field Test and Numerical Simulation on the Long-Term Thermal Response of PHC Energy Pile in Layered Foundation

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3873
Author(s):  
Guozhu Zhang ◽  
Ziming Cao ◽  
Yiping Liu ◽  
Jiawei Chen
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchange ◽  
Temperature Variation ◽  
Thermal Response ◽  
Ground Temperature ◽  
Short Term ◽  
Energy Pile ◽  
Backfill Soil ◽  
Short And Long Term

Investigation on the long-term thermal response of precast high-strength concrete (PHC) energy pile is relatively rare. This paper combines field experiments and numerical simulations to investigate the long-term thermal properties of a PHC energy pile in a layered foundation. The major findings obtained from the experimental and numerical studies are as follows: First, the thermophysical ground properties gradually produce an influence on the long-term temperature variation. For the soil layers with relatively higher thermal conductivity, the ground temperature near to the energy pile presents a slowly increasing trend, and the ground temperature response at a longer distance from the center of the PHC pile appears to be delayed. Second, the short- and long-term thermal performance of the PHC energy pile can be enhanced by increasing the thermal conductivity of backfill soil. When the thermal conductivities of backfill soil in the PHC pile increase from 1 to 4 W/(m K), the heat exchange amounts of energy pile can be enhanced by approximately 30%, 79%, 105%, and 122% at 1 day and 20%, 47%, 59%, and 66% at 90 days compared with the backfill water used in the site. However, the influence of specific heat capacity of the backfill soil in the PHC pile on the short-term or long-term thermal response can be ignored. Furthermore, the variation of the initial ground temperature is also an important factor to affect the short-and-long-term heat transfer capacity and ground temperature variation. Finally, the thermal conductivity of the ground has a significant effect on the long-term thermal response compared with the short-term condition, and the heat exchange rates rise by about 5% and 9% at 1 day and 21% and 37% at 90 days as the thermal conductivities of the ground increase by 0.5 and 1 W/(m K), respectively.

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