scholarly journals The Thermal and Settlement Characteristics of Crushed-Rock Structure Embankments of the Qinghai-Tibet Railway in Permafrost Regions Under Climate Warming

2021 ◽  
Vol 9 ◽  
Author(s):  
Qihang Mei ◽  
Bin Yang ◽  
Ji Chen ◽  
Jingyi Zhao ◽  
Xin Hou ◽  
...  
Keyword(s):  
Climate Warming ◽  
Cold Season ◽  
Base Layer ◽  
Crushed Rock ◽  
Permafrost Degradation ◽  
Rock Layer ◽  
Design Code ◽  
Rock Structure ◽  
The Stability ◽  
Permafrost Regions

The temperature difference at the top and bottom of the crushed-rock layer can drive the heat convection inside. Based on this mechanism, crushed-rock structures with different forms are widely used in the construction and maintenance of the Qinghai-Tibet Railway as cooling measures in permafrost regions. To explore the stability of different forms of crushed-rock structure embankments under climate warming, the temperature and deformation data of a U-shaped crushed-rock embankment (UCRE) and a crushed-rock revetment embankment (CRRE) are analysed. The variations in temperature indicate that permafrost beneath the natural sites and embankments is degrading but at different rates. The thermal regime of ground under the natural site is only affected by climate warming, while that under embankment is also affected by embankment construction and the cooling effect of the crushed-rock structure. These factors make shallow permafrost degradation beneath the embankments slower than that beneath the natural sites and deep permafrost degradation faster than that beneath the natural sites. Moreover, the convection occurring in the crushed-rock base layer during the cold season makes the degradation of permafrost beneath the UCRE slower than that in the CRRE. The faster degradation of permafrost causes the accumulated deformation of the CRRE to be far greater than that of the UCRE, which may exceed the allowable value of the design code. The analysis shows that the stability of the UCRE meets the engineering requirements and the CRRE needs to be strengthened in warm and ice-rich permafrost regions under climate warming.

Remedying embankment thaw settlement in a warm permafrost region with thermosyphons and crushed rock revetment

2012 ◽  
Vol 49 (9) ◽  
pp. 1005-1014 ◽  
Author(s):  
Wei Ma ◽  
Zhi Wen ◽  
Yu Sheng ◽  
Qingbai Wu ◽  
Dayan Wang ◽  
...  
Keyword(s):  
Crushed Rock ◽  
Permafrost Region ◽  
Permafrost Degradation ◽  
Remedial Measures ◽  
Two Phase ◽  
Permafrost Warming ◽  
Railway System ◽  
Thaw Settlement ◽  
The Stability ◽  
Permafrost Regions

Due to the special engineering geology characteristics of permafrost, construction in permafrost regions tends to result in serious permafrost-related engineering problems. Thaw settlement induced by permafrost degradation is the principal challenge for railway construction on the Qinghai-Tibetan Plateau. It threatens the stability and safety of the railway system, especially in warm and ice-rich permafrost regions. Thaw settlement in section DK1139+780 along the Qinghai-Tibetan railway is a potential risk to the safety of the railway, and a combination of closed thermosyphons and crushed rock revetment was used to remedy permafrost warming and thaw settlement of the embankment. Based on ground temperatures and embankment deformations observed at this site since 2002, the effects of the remedial measures were evaluated. The results show that the remedial measures lowered the ground temperature and raised the permafrost table. The crushed rock slope protection acted as an insulation layer and reduced heat flux into the embankment. The thermosyphons lowered the permafrost temperature and had a good cooling effect on the underlying permafrost. The results show that the remedial measures using two-phase thermosyphons and crushed rock revetment decreased the settlement of the embankment and improved the stability of the railway system.

Effect of Vibrating Load on Grain Size Distribution of Crushed Rock Layer

2010 ◽  
Vol 168-170 ◽  
pp. 663-668
Author(s):  
Li Jun Yang ◽  
Wen Hui Bai ◽  
Bin Xiang Sun ◽  
Shuang Jie Wang ◽  
Jin Zhao Zhang
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Crushed Rock ◽  
Rock Layer ◽  
Fines Content ◽  
The Matrix ◽  
Study Laboratory ◽  
Permafrost Regions ◽  
Highway Embankment

For the construction of the proposed Qinghai-Tibet Express Highway in warm and ice-rich permafrost regions, it will be necessary to utilize the new technique of cooling the ground temperature by the coarsely crushed rock layer with a low fines content, instead of the traditional measures taken to increase simply thermal resistances, so as to protect from damage to highway embankment due to thaw settlement. The vibrating loads such as wheel load and tamping load may cause the breakage and abrasion of the matrix grains in the coarsely crushed rock layer. This results in decreasing of grain size and increasing of fines content in the crushed rock layer, thus decreasing the porosity of crushed rock layer. The smaller porosity of crushed rock layer may weaken the cooling effect of buoyancy-driven natural convection of the pore air in the crushed rock layer of the highway embankment, thus resulting in instability and failure of the embankment structure in permafrost regions. Under these conditions, the influence of vibrating load on the grain size distribution of the coarsely crushed rock layer has to be investigated experimentally. In the present study, laboratory experiments on the grain size variation of the coarsely crushed rock layer under vertically vibrating loads were carried out. The test results show that the vibrating load can cause the breakage and abrasion of the matrix grains in the coarsely crushed rock layer and the shapes of coarely crushed rock grain tend to be non-angular.

scholarly journals Reduced microbial stability in the active layer is associated with carbon loss under alpine permafrost degradation

2021 ◽  
Vol 118 (25) ◽  
pp. e2025321118
Author(s):  
Ming-Hui Wu ◽  
Sheng-Yun Chen ◽  
Jian-Wei Chen ◽  
Kai Xue ◽  
Shi-Long Chen ◽  
...  
Keyword(s):  
Active Layer ◽  
Tibet Plateau ◽  
Permafrost Degradation ◽  
Soil C ◽  
C Cycling ◽  
Microbial Stability ◽  
The Stability ◽  
Qinghai Tibet Plateau ◽  
Permafrost Regions

Permafrost degradation may induce soil carbon (C) loss, critical for global C cycling, and be mediated by microbes. Despite larger C stored within the active layer of permafrost regions, which are more affected by warming, and the critical roles of Qinghai-Tibet Plateau in C cycling, most previous studies focused on the permafrost layer and in high-latitude areas. We demonstrate in situ that permafrost degradation alters the diversity and potentially decreases the stability of active layer microbial communities. These changes are associated with soil C loss and potentially a positive C feedback. This study provides insights into microbial-mediated mechanisms responsible for C loss within the active layer in degraded permafrost, aiding in the modeling of C emission under future scenarios.

scholarly journals Impacts of Permafrost Degradation on Carbon Stocks and Emissions under a Warming Climate: A Review

Atmosphere ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1425
Author(s):  
Huijun Jin ◽  
Qiang Ma
Keyword(s):  
Organic Carbon ◽  
Climate Warming ◽  
Carbon Emissions ◽  
Ecosystem Model ◽  
Carbon Stocks ◽  
Carbon Pools ◽  
Permafrost Degradation ◽  
Arctic Ecosystems ◽  
Warming Climate ◽  
Permafrost Regions

A huge amount of carbon (C) is stored in permafrost regions. Climate warming and permafrost degradation induce gradual and abrupt carbon emissions into both the atmosphere and hydrosphere. In this paper, we review and synthesize recent advances in studies on carbon stocks in permafrost regions, biodegradability of permafrost organic carbon (POC), carbon emissions, and modeling/projecting permafrost carbon feedback to climate warming. The results showed that: (1) A large amount of organic carbon (1460–1600 PgC) is stored in permafrost regions, while there are large uncertainties in the estimation of carbon pools in subsea permafrost and in clathrates in terrestrial permafrost regions and offshore clathrate reservoirs; (2) many studies indicate that carbon pools in Circum-Arctic regions are on the rise despite the increasing release of POC under a warming climate, because of enhancing carbon uptake of boreal and arctic ecosystems; however, some ecosystem model studies indicate otherwise, that the permafrost carbon pool tends to decline as a result of conversion of permafrost regions from atmospheric sink to source under a warming climate; (3) multiple environmental factors affect the decomposability of POC, including ground hydrothermal regimes, carbon/nitrogen (C/N) ratio, organic carbon contents, and microbial communities, among others; and (4) however, results from modeling and projecting studies on the feedbacks of POC to climate warming indicate no conclusive or substantial acceleration of climate warming from POC emission and permafrost degradation over the 21st century. These projections may potentially underestimate the POC feedbacks to climate warming if abrupt POC emissions are not taken into account. We advise that studies on permafrost carbon feedbacks to climate warming should also focus more on the carbon feedbacks from the rapid permafrost degradation, such as thermokarst processes, gas hydrate destabilization, and wildfire-induced permafrost degradation. More attention should be paid to carbon emissions from aquatic systems because of their roles in channeling POC release and their significant methane release potentials.

Effect of Crushed Rock Layer Width on Natural Convection Cooling of Highway Embankment in Permafrost Regions

2012 ◽  
Vol 204-208 ◽  
pp. 1638-1643 ◽  
Author(s):  
Li Jun Yang ◽  
Bin Xiang Sun ◽  
Wei Wang ◽  
Qi Liu
Keyword(s):  
Natural Convection ◽  
Crushed Rock ◽  
Rock Layer ◽  
Layer Width ◽  
Variable Permeability ◽  
Cold Energy ◽  
Convection Cooling ◽  
Winter Time ◽  
Permafrost Regions ◽  
Highway Embankment

For the construction of the proposed Qinghai-Tibet Express Highway in permafrost regions, it will be necessary to use the new technique of cooling the ground temperature by the coarsely crushed rock layer with a low fines content. The heat convection governing equations based on airflow function in variable permeability porous crushed rock layer are derived. Comparison of the cooling capability of winter-time natural convection in the crushed rock highway embankments with various widths of crushed rock layer and an air-permeable side slope surface were studied using a finite element method. The result indicates that the cooling capability of natural convection within the crushed rock highway embankment with a crushed rock layer width of 12 m is stronger than that with a crushed rock layer width of 10 m. Under the same temperature and pressure boundaries, the storage of cold energy in the foundation soils below the wider crushed rock highway embankment due to natural convective heat transfer is larger than that below the narrower one.

The Stability Analysis of Slope of Shegang Protecting Dyke

2011 ◽  
Vol 261-263 ◽  
pp. 1841-1845
Author(s):  
Hui Qin Yao
Keyword(s):  
Stability Analysis ◽  
Working Conditions ◽  
Saturation Line ◽  
Dam Safety ◽  
Design Code ◽  
Embankment Dam ◽  
Safe Operation ◽  
Calculation Results ◽  
The Stability ◽  
Reinforcement Design

Appraisal of dam slope safety is essential for security and stability of the dyke that has been constructed for many years. According to the requirements of the appraisal of dam safety, the stability analysis of slope of Shegang dyke has been carried out by using Sweden circular-arc method, Bishop method, Engineer Corps method and Lowe method four methods under many kinds of working conditions and some conditions when the saturation line raising. Combined with the design code form embankment dam, the calculation results can be analyzed. The analysis can show that the security indexes of anti-slide under four kinds of working conditions and some conditions when the saturation line raising meet the requirements of the design code. This can provide basis for the reinforcement design of the dam, which also has a certain directive significance for the safe operation and observation of the dam in the future.

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