Ten years of ground temperature data(2003–2013) indicate that the long-term thermal regimes within embankments of the Qinghai-Tibet Railway(QTR) vary significantly with different embankment structures. Obvious asymme...Ten years of ground temperature data(2003–2013) indicate that the long-term thermal regimes within embankments of the Qinghai-Tibet Railway(QTR) vary significantly with different embankment structures. Obvious asymmetries exist in the ground temperature fields within the traditional embankment(TE) and the crushed-rock basement embankment(CRBE). Measurements indicate that the TE and CRBE are not conducive to maintaining thermal stability. In contrast, the ground temperature fields of both the crushed-rock sloped embankment(CRSE) and the U-shaped crushed-rock embankment(UCRE) were symmetrical. However, the UCRE gave better thermal stability than the CRSE because slow warming of deep permafrost was observed under the CRSE. Therefore, the UCRE has the best long-term effect of decreasing ground temperature and improving the symmetry of the temperature field. More generally, it is concluded that construction using the cooling-roadbed principle meets the design requirements for long-term stability of the railway and for train transport speeds of 100 km h?1. However, temperature differences between the two shoulders, which exist in all embankments shoulders, may cause potential uneven settlement and might require maintenance.展开更多
For the purpose of enhancing air convection and controlling solar radiation, a new crushed-rock slope embankment design combined with a sun-shade measure is proposed. A newly designed embankment was constructed in the...For the purpose of enhancing air convection and controlling solar radiation, a new crushed-rock slope embankment design combined with a sun-shade measure is proposed. A newly designed embankment was constructed in the Tuotuohe section of the Qinghai-Tibet Railway and a field-testing experiment was carried out to determine its convection and temperature characteristics. The results show that distinct air convection occurred in the crushed-rock layer of the new embankment, especially in cold seasons, which was enhanced when it flowed upwards along the slope. This preliminarily indicated that the new design of the embankment slope was good for reinforcing air convection in the crushed-rock layer. The frequent fluctuations of the convection speed and the environmental wind speed were in good agreement, suggesting that the convection in the crushed rock primarily came from the ambient wind. It was also preliminarily determined that the new embankment had a better cooling effect and sun-shade effect for decreasing the temperature of the embankment slope compared with a traditional crushed-rock slope embankment, and the mean temperature difference between them was up to 1.7 °C. The mean annual temperature at the bottom boundary of the crushed-rock layer was obviously lower than that at the top boundary, and heat flux calculation showed that the shallow soil beneath the embankment slope was weakly releasing heat, all of which indicated that the new embankment slope design was beneficial to the thermal stability of the embankment. This study is helpful in providing some references for improved engineering design and maintenance of roadbeds in permafrost regions.展开更多
Based on the data from the pitting, geoelectrical prospectings, temperature measuring, and the divided layers frost-heaving instruments, this paper, first, discusses the structure features of active layers in this reg...Based on the data from the pitting, geoelectrical prospectings, temperature measuring, and the divided layers frost-heaving instruments, this paper, first, discusses the structure features of active layers in this region, and proves the presence of the bowlshaped frost table in the stone circles area. Second, it analyses the temperature distributive rule in the active layer, meantime, according to the vertical-profile parameters of granularity, clay mineral, salt content and resistivities, it also discusses the different features of permafrost structure and their control actions on the periglacial landform development between high and low places. It suggests that the four-layer structure should exist in the permafrost region (including under-bedrock), that is, active layer, frost sand and gravels layer, frost volcanic rock permeated by sea water, and frost volcanic rock unpermeated by sea water. Finally, the permafrost table and its vertical gradient are deduced.展开更多
Safe operation and performance of dams is one of the key issues in permafrost regions. At present, the existing dams are 40–45 years old and they are reaching their design life limit. Intensive geocryological proces...Safe operation and performance of dams is one of the key issues in permafrost regions. At present, the existing dams are 40–45 years old and they are reaching their design life limit. Intensive geocryological processes（thermokarst, thermal erosion, frost heaving, suffosion, concentrated seepage along the voids left by melt ice and others） begin to develop at the early stages of construction. These processes are even more intensive under severe climatic conditions of the permafrost zone due to the large thermal and moisture gradients and the resulting complex thermal stress-strain state in the structures. Determining safety criteria is a critical and difficult task in dam safety management. The existing procedures need to be continuously refined and improved depending on dam importance class. Some researchers recommend introducing process development criteria（stability, destabilization, and extremality） for more objective assessment of dam safety, in addition to the existing two condition criteria. In other words, they call for a multi-factor dam – environment interaction system. A case study of safety declaration for an existing dam is presented.展开更多
Background:Soil microorganisms in the thawing permafrost play key roles in the maintenance of ecosystem function and regulation of biogeochemical cycles.However,our knowledge of patterns and drivers of permafrost micr...Background:Soil microorganisms in the thawing permafrost play key roles in the maintenance of ecosystem function and regulation of biogeochemical cycles.However,our knowledge of patterns and drivers of permafrost micro-bial communities is limited in northeastern China.Therefore,we investigated the community structure of soil bacteria in the active,transition and permafrost layers based on 90 soil samples collected from 10 sites across the continuous permafrost region using high-throughput Illumina sequencing.Results:Proteobacteria(31.59%),Acidobacteria(18.63%),Bacteroidetes(9.74%),Chloroflexi(7.01%)and Actinobacteria(6.92%)were the predominant phyla of the bacterial community in all soil layers;however,the relative abundances of the dominant bacterial taxa varied with soil depth.The bacterial community alpha-diversity based on the Shannon index and the phylogenetic diversity index both decreased significantly with depth across the transition from active layer to permafrost layer.Nonmetric multidimensional scaling analysis and permutation multivariate analysis of variance revealed that microbial community structures were significantly different among layers.Redundancy analysis and Spearman’s correlation analysis showed that soil properties differed between layers such as soil nutrient content,temperature and moisture mainly drove the differentiation of bacterial communities.Conclusions:Our results revealed significant differences in bacterial composition and diversity among soil layers.Our findings suggest that the heterogeneous environmental conditions between the three soil horizons had strong influences on microbial niche differentiation and further explained the variability of soil bacterial community structures.This effort to profile the vertical distribution of bacterial communities may enable better evaluations of changes in microbial dynamics in response to permafrost thaw,which would be beneficial to ecological conservation of permafrost ecosystems.展开更多
基金supported by the National Basic Research Program of China(Grant No.2012CB026101)the Western Project Program of the Chinese Academy of Sciences(Grant No.KZCX2-XB3-19)+1 种基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(Grant No.41121061)the National Sci-Tech Support Plan(Grant No.2014BAG05B05)
文摘Ten years of ground temperature data(2003–2013) indicate that the long-term thermal regimes within embankments of the Qinghai-Tibet Railway(QTR) vary significantly with different embankment structures. Obvious asymmetries exist in the ground temperature fields within the traditional embankment(TE) and the crushed-rock basement embankment(CRBE). Measurements indicate that the TE and CRBE are not conducive to maintaining thermal stability. In contrast, the ground temperature fields of both the crushed-rock sloped embankment(CRSE) and the U-shaped crushed-rock embankment(UCRE) were symmetrical. However, the UCRE gave better thermal stability than the CRSE because slow warming of deep permafrost was observed under the CRSE. Therefore, the UCRE has the best long-term effect of decreasing ground temperature and improving the symmetry of the temperature field. More generally, it is concluded that construction using the cooling-roadbed principle meets the design requirements for long-term stability of the railway and for train transport speeds of 100 km h?1. However, temperature differences between the two shoulders, which exist in all embankments shoulders, may cause potential uneven settlement and might require maintenance.
基金supported by the Western Project Program of the Chinese Academy of Sciences (No. KZCX2-XB3-19)the National Key Basic Research Program of China, 973 Program (No. 2012CB026101)
文摘For the purpose of enhancing air convection and controlling solar radiation, a new crushed-rock slope embankment design combined with a sun-shade measure is proposed. A newly designed embankment was constructed in the Tuotuohe section of the Qinghai-Tibet Railway and a field-testing experiment was carried out to determine its convection and temperature characteristics. The results show that distinct air convection occurred in the crushed-rock layer of the new embankment, especially in cold seasons, which was enhanced when it flowed upwards along the slope. This preliminarily indicated that the new design of the embankment slope was good for reinforcing air convection in the crushed-rock layer. The frequent fluctuations of the convection speed and the environmental wind speed were in good agreement, suggesting that the convection in the crushed rock primarily came from the ambient wind. It was also preliminarily determined that the new embankment had a better cooling effect and sun-shade effect for decreasing the temperature of the embankment slope compared with a traditional crushed-rock slope embankment, and the mean temperature difference between them was up to 1.7 °C. The mean annual temperature at the bottom boundary of the crushed-rock layer was obviously lower than that at the top boundary, and heat flux calculation showed that the shallow soil beneath the embankment slope was weakly releasing heat, all of which indicated that the new embankment slope design was beneficial to the thermal stability of the embankment. This study is helpful in providing some references for improved engineering design and maintenance of roadbeds in permafrost regions.
基金The research is supported by the State Antarctic Committee and the National Natural Science Foundation of China.
文摘Based on the data from the pitting, geoelectrical prospectings, temperature measuring, and the divided layers frost-heaving instruments, this paper, first, discusses the structure features of active layers in this region, and proves the presence of the bowlshaped frost table in the stone circles area. Second, it analyses the temperature distributive rule in the active layer, meantime, according to the vertical-profile parameters of granularity, clay mineral, salt content and resistivities, it also discusses the different features of permafrost structure and their control actions on the periglacial landform development between high and low places. It suggests that the four-layer structure should exist in the permafrost region (including under-bedrock), that is, active layer, frost sand and gravels layer, frost volcanic rock permeated by sea water, and frost volcanic rock unpermeated by sea water. Finally, the permafrost table and its vertical gradient are deduced.
文摘Safe operation and performance of dams is one of the key issues in permafrost regions. At present, the existing dams are 40–45 years old and they are reaching their design life limit. Intensive geocryological processes（thermokarst, thermal erosion, frost heaving, suffosion, concentrated seepage along the voids left by melt ice and others） begin to develop at the early stages of construction. These processes are even more intensive under severe climatic conditions of the permafrost zone due to the large thermal and moisture gradients and the resulting complex thermal stress-strain state in the structures. Determining safety criteria is a critical and difficult task in dam safety management. The existing procedures need to be continuously refined and improved depending on dam importance class. Some researchers recommend introducing process development criteria（stability, destabilization, and extremality） for more objective assessment of dam safety, in addition to the existing two condition criteria. In other words, they call for a multi-factor dam – environment interaction system. A case study of safety declaration for an existing dam is presented.
基金supported by the National Basic Research Program of China(973 program,2013CBA01807)the National Natural Science Foundation of China(32001127).
文摘Background:Soil microorganisms in the thawing permafrost play key roles in the maintenance of ecosystem function and regulation of biogeochemical cycles.However,our knowledge of patterns and drivers of permafrost micro-bial communities is limited in northeastern China.Therefore,we investigated the community structure of soil bacteria in the active,transition and permafrost layers based on 90 soil samples collected from 10 sites across the continuous permafrost region using high-throughput Illumina sequencing.Results:Proteobacteria(31.59%),Acidobacteria(18.63%),Bacteroidetes(9.74%),Chloroflexi(7.01%)and Actinobacteria(6.92%)were the predominant phyla of the bacterial community in all soil layers;however,the relative abundances of the dominant bacterial taxa varied with soil depth.The bacterial community alpha-diversity based on the Shannon index and the phylogenetic diversity index both decreased significantly with depth across the transition from active layer to permafrost layer.Nonmetric multidimensional scaling analysis and permutation multivariate analysis of variance revealed that microbial community structures were significantly different among layers.Redundancy analysis and Spearman’s correlation analysis showed that soil properties differed between layers such as soil nutrient content,temperature and moisture mainly drove the differentiation of bacterial communities.Conclusions:Our results revealed significant differences in bacterial composition and diversity among soil layers.Our findings suggest that the heterogeneous environmental conditions between the three soil horizons had strong influences on microbial niche differentiation and further explained the variability of soil bacterial community structures.This effort to profile the vertical distribution of bacterial communities may enable better evaluations of changes in microbial dynamics in response to permafrost thaw,which would be beneficial to ecological conservation of permafrost ecosystems.
