Technological monitoring of subgrade construction on high-temperature permafrost

Three stages of complex technological monitoring for the increase of high-temperature-permafrost soil bearing capacity are described. The feasibility of process monitoring to improve the targeted strength properties of subgrade bases on frozen soils is demonstrated. The rationale for the necessity of predictive modeling of freeze-thaw actions during the subgrade construction period is provided.     

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.     

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.     

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.     

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.     

疏勒河源冻土区高寒草甸土壤碳氮含量特征

土壤碳氮是高寒植被响应多年冻土区生态环境变化的重要营养和能源物质,但对其调查仍以生长季的单次采样为主,缺乏对其他季节的研究,这对于准确把握多年冻土区土壤碳氮含量及储量评估存在明显局限性。为此,本研究以青藏高原东北缘祁连山西段疏勒河源多年冻土区高寒草甸为对象,对0—50 cm土层土壤有机碳（Soil Organic Carbon, SOC）、全氮（Total Nitrogen, TN）含量及其比值（C/N）的剖面分布和季节变化及其影响因素进行分析。结果表明：（1）SOC、TN剖面分布规律一致,0—10 cm土层均显著高于10—50 cm各层（P<0.05）,0—50 cm深度仅秋季逐渐下降,而春夏冬季0—30 cm递减。（2）SOC、TN含量存在季节变化,SOC表现为夏季>冬季>春季>秋季,TN表现为春秋冬季含量一致,夏季略低。（3）C/N季节变化显著,夏季显著最高,秋季显著最低（P<0.05）。（4）土壤含水量和生物量是影响SOC、TN及C/N剖面分布和季节变化的关键因素。（5）夏季土壤碳氮密度均高于全年平均。可见,仅单一节点（生长季为主）调查以表征全年土壤碳氮储量存在高估趋势。     

Stress states of thawed soil subgrade

The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained.     

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.     

Accounting for the solar radiation in thermal regime prediction for railway subgrade in cold regions

This paper presents a comparative analysis of simulation processes of seasonal freezing-thawing of railway subgrade and permafrost degradation, with and without accounting for solar radiation. Also, the effect of sun screens to reduce the degradation of subgrade permafrost under different climatic conditions is numerically substantiated. And finally, the temperature criterion of the origination of permafrost is illustrated.     

Evaluation of embankment foundation creep in conditions of deep bedding of roof in permafrost soils

Railroad operating experience in permafrost conditions has shown that deformations of embankments on thawing foun-dations last for a long time. After an initial period of heat settlement due to permafr...     

南疆盐渍土路基盐-冻胀变形综合防治技术研究

盐渍土盐-冻胀变形对新疆南疆地区的道路路基造成了不同程度的破坏,尤其对南疆新建城市阿拉尔市和图木舒克市的城市道路造成了严重的变形破坏.根据南疆盐渍土工程性质及盐-冻胀变形试验研究结果,作者总结提出了"一个加强、两个严格、三个注重"的盐渍土路基盐-冻胀变形综合防治原则和"五步骤"综合防治技术与工程措施,在南疆阿拉尔市胜利...     

New soil thermal stabilization systems for building fundaments in permafrost regions

This paper describes new building construction methods that utilize soil thermal stabilization regimes to compensate for negative environmental warming and anthropogenic factors that impair fundament stability. Based on long-standing research, the Fundamentstroyarkos Company (FSA) of Tyumen, Russia has developed four primary seasonally active cooling devices (SCDs) that maintain soil in the frozen state, which are now extensively used on oil and gas facilities located in cold regions of Russia. This paper reports on the testing and validation of these SCDs in experimental conditions. On this basis, designs and technologies for building bases and foundations on permafrost with use of soil thermal stabilization systems, using carbon dioxide as the heat-transfer agent, were developed.     

Subgrade-reinforcement techniques for the dangerously deforming sections of railway lines in the north of the Russian Far East

This paper lists difficult railway construction conditions that are typical for the northern areas of the Russian Far East. Permafrost-bound issues of railway and highway construction and operation are described. Some of the authors'' developments for subgrade stabilization in the foregoing conditions are given as examples.     

Quantitative characteristics of microorganisms in permafrost at different depths and their relation to soil physicochemical properties

Microorganisms in permafrost can live in cold environments due to coadapted physicochemical processes in this environment. In this paper, the relation between microbial number and soil physicochemical properties at the headwaters area of the Urumqi River is analyzed by using fluorescence microscopy counting and oligo-culture techniques. In total, 20 samples from a 200-cm permafrost core were used as study materials. The study reveals that the number of culturable bacteria has a significantly positive correlation with soil water content, total carbon and total nitrogen concentrations, and a significantly negative correlation with soil pH value. In addition, the ratio of culturable bacteria to total cell number decreases with depths. The results demonstrate that the number of culturable bacteria in permafrost is closely correlated with soil physicochemical properties and depositional age.     

Effects of dune stabilization on vegetation characteristics and soil properties at multiple scales in Horqin Sandy Land, Northern China

Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however information on how dune stabilization influences vegetation and soil at different spatial scales...     

Spatiotemporal variability of permafrost degradation on the Qinghai-Tibet Plateau

Based on data from six meteorological stations in the permafrost regions, 60 boreholes for long-term monitoring of permafrost temperatures, and 710 hand-dug pits and shallow boreholes on the Qinghai-Tibet Plateau (QTP), the spatiotemporal variability of permafrost degradation was closely examined in relation to the rates of changes in air, surface, and ground temperatures. The decadal averages and increases in the mean annual air temperatures (MAATs) from 1961–2010 were the largest and most persistent during the last century. MAATs rose by 1.3 °C, with an average increase rate of 0.03 °C/yr. The average of mean annual ground surface temperatures (MAGSTs) increased by 1.3 °C at an average rate of 0.03 °C/yr. The rates of changes in ground temperatures were ?0.01 to 0.07 °C/yr. The rates of changes in the depths of the permafrost table were ?1 to +10 cm/yr. The areal extent of permafrost on the QTP shrank from about 1.50×10⁶ km² in 1975 to about 1.26×10⁶ km² in 2006. About 60% of the shrinkage in area of permafrost occurred during the period from 1996 to 2006. Due to increasing air temperature since the late 1980s, warm (>?1 °C) permafrost has started to degrade, and the degradation has gradually expanded to the zones of transitory (?1 to ?2 °C) and cold (相似文献   

The convection cooling system of the Yakutsk permafrost seed repository

Temperature is critical to maintaining seed viability under long-term storage conditions. It has been common practice to use refrigeration systems to maintain required storage temperatures. A seed repository constructed in permafrost in Yakutsk, Russia is the first seed storage facility that relies solely on natural cold. This paper describes the design and performance of the cooling system of the repository. An innovative aspect of the cooling system is that it utilizes the patterns of temperature wave propagation in permafrost. Predicted and measured ground temperatures for the first year of operation are presented and analyzed. Results indicate that convection air cooling systems can be used to control the temperature regime in underground facilities in 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。     

Experimental research on physical properties of saline soil subgrade filler in Chaerhan region

In order to improve the engineering stability of saline soil of high chloride content in the Chaerhan salt lake region, six typical characteristics saline soil samples were selected, and tests on their...     

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.