To the issue of stabilization of permafrost soil subgrade

This paper summarizes an analysis of consequences of railway subgrade construction and maintenance solutions in northern areas of the Russian Far East. An idea of the natural long-term stabilization of the subgrade-base geotechnical system is presented. Proposals to improve the decision-making of construction and engineering solutions are formulated.     

Geotechnical problems of construction on permafrost in Mongolia

Permafrost is found on 63%of the territory of Mongolia. This paper provides evidence that the main influences on per-mafrost formation are meso and micro factors of climate and geographical location. R...     

Analysis of temperature field characteristics based on subgrade site measurements of Harbin-Qiqihar High-speed Railway in a deep seasonal frozen soil region

Recent years have seen a large number of high-speed railways built and will be built in seasonal frozen soil regions of China. Although high-speed railways are characterized by being fast, comfortable and safe, higher standards for deformation of the railways' frozen subgrade are required. Meanwhile, changes in subgrade soil temperatures are the main factors affecting the deformation of frozen subgrade. Therefore, this paper selected typical test subgrade sections of the Harbin–Qiqihar Line, a special line for passenger transport built in the deep seasonal frozen soil regions of China, to monitor field temperatures. Also, the temperature changing laws of railways' subgrade in this region was analyzed by using testing data, the aim of which is to provide a technical support for future design and construction of buildings and structures in a deep seasonal frozen soil region.     

Technological risk regulation of the subgrade base stability in permafrost areas

Maintenance and risk estimation of a weak roadbed condition during the construction period are described.Risk-management procedure for unstable,weak soils is proposed through adjusting the technological loads and real-time monitoring of their influence.The efficiency of implementing maximum allowable vibroloads and the drainage system for strengthening weak soils is shown in the example of the Northern Latitudinal Railway area.     

Analysis of bearing capacity of pile foundation in discontinued permafrost regions

Piles are the main building foundation in permafrost regions. Thawing the permafrost foundation would have a negative effect on a pile, and may cause damage to the building. This paper focuses on the effects of negative friction force due to the melt of permafrost, and presents four calculated methods for bearing capacity of a pile. An engineering station was taken as an example, where the lengths of a pile were compared based on four methods. Finally, quick field load tests were carried out, and some meaningful conclusions are presented. Thus, these analytical results can be used to design a pile for permafrost regions.     

Temperature monitoring of the XPS board insulated subgrade along the newly constructed Gonghe-Yushu Highway in permafrost regions

On the basis of on-site measured data of the newly constructed Gonghe-Yushu Highway in a permafrost region, this paper analyzed thermal conditions of the subgrade with XPS insulated board according to different selected monitoring sections in various locations. We also summarized the geothermal distribution and change rules of subgrade with XPS insulation board under the asphalt pavement in summarized a high temperature frozen soil region. It is suggested that the shoulder of subgrade with XPS insulation board be widen to a reasonable width so as to keep the subgrade stable.     

Study on the technology for highway construction and engineering practices in permafrost regions

In order to systemically summarize and integrate technology of highway construction in permafrost regions on the Qinghai-Tibet Plateau,we studied disciplines and mechanisms of formation and development of problems and challenges in highway engineer-ing in high-altitude permafrost regions based on construction experiences for 50 years and on 30 years of research regarding the Qinghai-Tibet and Xikang highways.Embankments,pavements,bridges,and countermeasures for ecosystem protection in per-mafrost regions were the main study objects.We combined extensive analysis of key problems of engineering stability with inter-action between permafrost and highways,theoretical models,indoor tests,and field tests to reveal the interaction between em-bankments,pavements,bridge piles,and permafrost.In this paper,we propose a series of engineering measures for highway sta-bility,design parameters,key indexes for pavement durability in low temperature,relationships between re-freezing time of bridge-pile foundation and strength development as well as ecosystem recovery in high-latitude cold regions;these eventually form a construction technology package for permafrost regions.     

Discussion on the relationship between longitudinal cracks and alignment of subgrade in permafrost regions

At present, embankment longitudinal cracks are a major problem in highways through permafrost regions, and seriously affect traffic safety and the normal operations of the highway. In the past, roadbed height in permafrost regions was relatively low, and embankment cracks were rare and did not affect traffic safety. Thus, highway designers and researchers paid little attention to this problem, and they knew very little about distribution laws and mechanism of embankment longitudinal cracks. Due to this lack of knowledge, there is no uniform opinion on this problem, making it difficult to find measures that will mediate the impact of longitudinal cracks. Temperature is a major factor that affects and controls embankment stability in permafrost regions, especially in ice-rich and high-temperature regions, and solar radiation is the principal factor that determines surface temperatures. Under higher embankment, the difference of temperature will be larger between a sunny slope and a shady slope. Hence, the probability for longitudinal cracks generation is higher. In this paper, a survey and analysis of longitudinal cracks along the Qinghai-Tibet Highway were carried out. The longitudinal cracks are found to be related to the road strikes. Solar radiation is considered to play an important role in the generation of longitudinal cracks.     

Predictive modeling of the permafrost thermal regime in Russian railroad subgrade support systems

The goal of a predictive thermotechnical calculation is to model the behavior of the top permafrost boundary under current operational conditions as well as increasing average annual air temperatures that results in degradation of the permafrost layer. Numerical modeling was used to assess the efficient application of construction measures to create sustainable operation of the railroad. The numerical modeling was carried out in the programming complex FEM-models developed by geotechnical engineers of St. Petersburg, Russia under Prof. V. M. Ulitsky’s guidance. The Termoground Program as a part of the FEM-models enables the research of freezing, heaving and thawing in different design solutions. Research was carried out in space resolution for a year cycle. The performed model has shown that the designing measures accepted for permafrost protection from retreat in the subgrade support were generally effective.     

A system for automated monitoring of embankment deformation along the Qinghai-Tibet Railway in permafrost regions

At present, the monitoring of embankment deformation in permafrost regions along the Qinghai-Tibet Railway is mainly done manually. However, the harsh climate on the plateau affects the results greatly by lowering the observation frequency, so the manual monitoring can barely meet the observational demand. This research develops a system of automated monitoring of embankment deformation, and aims to address the problems caused by the plateau climate and the permafrost conditions in the region. The equipment consists of a monitoring module, a data collection module, a transmission module, and a data processing module. The field experiments during this program indicate that(1) the combined automated monitoring device overcame the problems associated with the complicated and tough plateau environment by means of wireless transmission and automatic analysis of the embankment settlement data;(2) the calibration of the combined settlement gauge at-20 °C was highly accurate, with an error rate always 0.5%;(3) the gauge calibration at high-temperature conditions was also highly accurate, with an error rate 0.5% even though the surface of the instrument reached more than 50 °C; and(4) compared with the data manually taken, the data automatically acquired during field monitoring experiments demonstrated that the combined settlement gauge and the automated monitoring system could meet the requirements of the monitoring mission in permafrost regions along the Qinghai-Tibet Railway.     

Dynamic response of wind turbine towers in warm permafrost

Wind is a great source of renewable energy in western Alaska.Consistent winds blow across the barren tundra underlain by warm permafrost in the winter season,when the energy demand is the highest.Foundation engineering in warm permafrost has always been a challenge in wind energy development.Degrading warm permafrost poses engineering issues to design,construction,and operation of wind turbines.This paper describes the foundation design of a wind turbine built in western Alaska.It presents a system for response monitoring and load assessment,and data collected from September 2013 to March 2014.The dynamic properties are assessed based on the monitoring data,and seasonal changes in the dynamic properties of the turbine tower-foundation system and likely resonance between the spinning blades and the tower structure are discussed.These analyses of a wind turbine in warm permafrost are valuable for designing or retrofitting of foundations in warm permafrost.     

Integrated geophysical surveys on railroads in permafrost areas

The zones of thawed ground in the permafrost area are most dangerous from engineer-geologist effect point of view. Detection of such zones, as making forecast of their movement is the main task of engi...     

A method used to determine the upper thermal boundary of subgrade based on boundary layer theory

In the numerical simulation of long-term subgrade temperature fields, the daily variation of soil temperature at a certain depth h is negligible. Such phenomenon is called the "boundary layer theory."Depth h is defined as the boundary layerthickness and the soil temperature at h is approximately equal to a temperature increment plus the average atmosphere temperature. In the past, the boundary layer thickness and temperature increment were usually extracted from monitored data in the field. In this paper, a method is proposed to determinate the boundary layer thickness and temperature increment. Based on the typical designs of highway or railway, the theoretical solution of boundary layer thickness is inferred and listed. Further, the empirical equation and design chart for determining the temperature increment are given in which the following factors are addressed, including solar radiation, equivalent thermal diffusivity and convective heat-transfer coefficient. Using these equations or design charts, the boundary layer thickness and temperature increment can be easily determined and used in the simulation of long-term subgrade temperature fields. Finally, an example is conducted and used to verify the method. The result shows that the proposed method for determining the upper thermal boundary of subgrade is accurate and practical.     

Strengthening long-term embankments maintained on permafrost soils

An analysis of the reasons for the displacements of long-term embankments maintained on permafrost soils indicates that they mainly occur due to plastic deformations in the layer of seasonal freezing and thawing; therefore, the reconstruction of permafrost is not effective in this case. It is proposed to strengthen these embankments with the help of using jet technology for cementation of the top layer of the roadbed. This approach is considered through the example of the deforming embankment on 6,278 km of the Turinskaya-Karymskaya section of the Trans-Siberian Railway.     

Systematization of features and requirements for geological survey of railroad subgrades functioning in cold regions

The operation of a railway track in cold regions results in the premature deformation of subgrade soils caused by significant temperature fluctuations and ecological imbalance. Identification and calculation of the thawing degree of permafrost soils, frost heaving of clays, and groundwater flooding require careful engineering and geological surveying. The paper describes the unique, long-standing experience of the university scientists connected with maintaining the Russian East-Siberian and Trans-Baikal Railways'' facilities. Specific features of and requirements for the surveying, depending on the geological and climatic conditions, are identified.     

Problems and countermeasures in construction of transmission line projects in permafrost regions

Construction of power transmission lines is becoming an important part of permafrost engineering in China.This paper reviews the construction status and problems of transmission lines in different countries,as well as corresponding solutions that would be of practical significance for sustainable engineering practices.Russia has the longest history of transmission line construction in permafrost areas,with transmission lines（mainly 220 kV and 500 kV） spanning approximately 100,000 km.However,all countries suffer from permafrost-related tower foundation stability problems caused by freezing-thawing hazards such as frost heave and thaw settlement,frost lifting,and harmful cryogenic phenomena.As point-line transmission line constructions,the lines,poles and towers should be reasonably selected and installed with a comprehensive consideration of frozen soil characteristics to effectively reduce the occurrence of freezing-thawing disasters.Reinforced concrete pile foundations are widely used in the permafrost regions,and construction in winter is also a universal practice.Moreover,facilitating engineering measures like thermosyphons are an effective way to reduce freezing-thawing hazards and to maintain the stability of tower foundations.     

Monitoring and analysis of ground temperature and deformation within Qinghai-Tibet Highway subgradein permafrost region

In order to study the stability of the Qinghai-Tibet Highway embankment at Chumaerhe in the permafrost region of northwest China, the ground temperature and deformation at different depths were monitored under the left and right shoulders of the embankment where thermosyphons were set up only on the left shoulder. Based on the monitored data, characteristics of ground temperature and deformation of the left and right shoulders are analyzed and discussed. The results show that the start time of freezing or thawing of the seasonal active layer was about one to two months later than that of the embankment body itself. The stability of each shoulder was mainly controlled by the settlement of different soil layers,whereasfrost heave of soil had scarcely any effect on the stability of the embankment. For the left shoulder, the settlement was mainly influenced by the seasonal active layer and then by the embankment body itself,due to freeze-thaw cycles which may change the soil properties; however, the permafrost layer remained fairly stable. For the right shoulder, creep of the warm permafrost layer was the main influence factor on its stability, followed by settlement of embankment body itself, and finally settlement of the seasonal active layer. Compared with the deformation of the left shoulder, the permafrost layer under the right shoulder was less stable, which indicates that the thermosyphons had a significantly positive effect on the stability of warm permafrost.     

大兴安岭多年冻土区森林土壤温室气体通量

多年冻土温室气体排放对全球气候变化有重要影响。采用静态暗箱—气相色谱法,于2016—2017年生长季（5—9月）,对大兴安岭多年冻土区兴安落叶松林、樟子松林和白桦林土壤二氧化碳（CO₂）、甲烷（CH₄）和氧化亚氮（N₂O）通量进行野外原位观测,对比分析温室气体通量的动态变化特征及其关键影响因子。结果表明：3种林型土壤CO₂通量范围为65.88~883.59 mg·m^-2·h^-1;CH₄通量范围为-93.29~-2.82 μg·m^-2·h^-1;N₂O通量范围为-5.31~45.22 μg·m^-2·h^-1。整个生长季兴安落叶松林、樟子松林和白桦林土壤均表现为CO₂、N₂O的排放源、CH₄的吸收汇,土壤CO₂和CH₄通量在不同林型和年际间差异显著。3种林型土壤CO₂通量与5 cm、10 cm和15 cm土壤温度呈极显著正相关（P < 0.01）;CH₄通量受土壤含水量和10 cm、15 cm土壤温度的影响较大（P < 0.05）;兴安落叶松林和樟子松林土壤N₂O通量与气温呈显著正相关（P < 0.05）,而白桦林土壤N₂O则与15 cm土壤温度呈显著负相关（P < 0.05）。基于100 a时间尺度计算温室气体全球综合增温潜势,3种林型土壤温室气体的排放对气候变暖具有正反馈作用。     

Investigation of monitoring system for high-speed railway subgrade frost heave

This paper presents methods for monitoring frost heave, device requirements, testing principals, and data analysis requirements, such as manual leveling observation, automatic monitoring (frost heave, frost depth, and moisture), track dynamic detection, and track status detection. We focused on the requirements of subgrade frost heave monitoring for high speed railways, and the relationship of different monitoring methods during different phases of the railway. The comprehensive monitoring system of high speed railway subgrade frost heave provided the technical support for dynamic design during construction and safe operation of the rail system.     

Composite technology of earthwork construction on taliks in cryolithic zones

This paper reviews construction and technological solutions for roadbeds in talik areas of permafrost soil, and proposes an integrated technology for prevention and elimination of taliks during constru...