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Evaluation of damage probability of railway embankments in permafrost regions in Qinghai–Tibet Plateau
Abstract
The Qinghai–Tibet Railway (QTR) has been operating since 2006. It crosses continuous permafrost regions in the Qinghai–Tibet Plateau. Half of these regions are characterized by high ground temperature and ice content, and slight changes in the permafrost may cause embankment damage. In this study, the deformed embankment data of the QTR collected from 2010 to 2018 were analyzed. The analysis results showed that the total length of deformed embankments of the QTR in the permafrost regions was 22.97 km, and the damage rate since its completion in 2006 was approximately 5.4%. The results also indicated that the embankments stabilized over time. In 2010, the deformed embankments that were reinforced consisted of 26 sites and were 7.64-km long, whereas in 2018, only a 0.48-km long site was reinforced. In this study, a damage probability model of the embankments is developed. The damage probability of the embankments along the QTR in permafrost regions was classified into five grades: slight, low, moderate, high, and extremely-high damage probability levels. The total lengths of embankment sections with slight, low, moderate, high, and extremely-high levels of damage probability are 190.38, 161.42, 61.72, 13.51, and 2.99 km, respectively. It is suggested that damage-free embankment sections with high and extremely-high levels of damage probability should be monitored more closely during railway embankment maintenance. This study provides a reference for the application of the logistic regression model to establish the damage probability model of railway embankments in permafrost regions.
... The QTR adopts a "bridges instead of roads" design approach for difficult terrains and areas with environmental protection concerns. A total of 156 km of the railway route utilize bridges instead of traditional embankments, resulting in the construction of 447 bridges [7,8]. Among them, the length of dry bridges reaches 125 km [9], leading to a significantly higher proportion of transition sections compared to conventional railways. ...
... Among them, the length of dry bridges reaches 125 km [9], leading to a significantly higher proportion of transition sections compared to conventional railways. Under the influence of climate change and human engineering activities, the deformations of the embankment-bridge transition section (EBTS) of the QTR have been serious in recent years [8,9]. Field investigation of 164 bridges within a 220 km of the permafrost hinterland of the QTR showed that 82.6 % of the EBTS exhibited settlement. ...
... Especially for the QTR, the embankment settlement of some EBTSs has exceeded 100 cm [9]. Monitoring data indicated that the settlement occurred in many EBTSs in the first year after QTR construction and has been aggravated year by year [8]. In the initial stage, the thickness of the ballast layer of QTR is only about 50 cm (Fig. 1a). ...
... • C [54,55]. In recent years, the temperature and precipitation in the QTEC have increased [55,56]. The permafrost in the study area is mainly characterized by high ground temperature and high ice content [25] and is also extremely sensitive to climate change, which makes the environmental risks faced by the infrastructures in the study area present with complex dynamic changes. ...
... [54,55]. In recent years, the temperature and precipitat in the QTEC have increased [55,56]. The permafrost in the study area is mainly charact ized by high ground temperature and high ice content [25] and is also extremely sensit to climate change, which makes the environmental risks faced by the infrastructures the study area present with complex dynamic changes. ...
Global warming has increased the security risk of permafrost environment in the Tibetan Plateau, which has been threatening infrastructures along the Qinghai–Tibet Engineering Corridor (QTEC). Combined with the traditional risk identification and the causal feedback relationship of system dynamics, the authors present a novel engineering environment risk identification model including five risk subsystems, i.e., regional geomorphology, climate change, ecological environment, permafrost environment and water environment. Our model could successfully identify the interaction relationships and transmission path among risk factors of the environment of the QTEC. The basic data calculation, interaction degree analysis and regional distribution characteristic analysis of the identified risk factors were carried out by using a geographic information system (GIS), a partial correlation analysis and a zoning analysis. The results show that the static factors (i.e., elevation, slope, aspect, relief degree of land surface and volume ice content) mainly affected the spatial distribution of environmental risk factors, while the climate change factors (i.e., mean annual air temperature, mean annual precipitation and surface solar radiation), among the dynamic factors, were the root factors of the dynamic changes in environmental risks. The model identified five types of parallel risk paths in the QTEC. This novel method and proposed model can be used to identify and assess multi-scale engineering environmental risks in the cryosphere.
... However, highway engineering has disrupted the thermal equilibrium of the original permafrost environment and caused subgrade diseases such as frost heave and thawing settlement. Among the various kinds of highway disease, thawing settlement is the main form of subgrade damage present in the QTEC, and it is caused by the increasing temperature of permafrost strata and the subsequent consolidation drainage and compression of the molten layer [4,5]. Furthermore, according to the IPCC report, the average air temperature is expected to rise by 0.3 • C every decade throughout the 21st century, with a potentially greater increase in high-altitude areas [6]. ...
As a result of global warming, the thawing settlement disasters of permafrost in the Qinghai–Tibet Engineering Corridor (QTEC) have intensified, which has serious effects on the safe operation of permafrost highway engineering. In this work, a prediction model for the thawing depth of permafrost subgrade in the QTEC under the climate warming scenario was established. Based on the survey results of permafrost ice content along the QTEC and the classification of thawing settlement risks, the zoning characteristics of thawing settlement of permafrost subgrade in the QTEC were obtained and analyzed. The results showed that the thawing depth of permafrost underlying the 26 m width subgrade in the QTEC will mainly remain below 9 m, and the area with a thawing depth of 6~9 m will have the widest spread within the next 20 years. The thawing settlement will be between 0.02 m and 5.45 m, with an average value of about 0.93 m after 20 years. Furthermore, after 50 years, the thawing depth of permafrost underlying the 26 m width subgrade will almost always be greater than 9 m, and the average thawing settlement will be about 1.12 m. Within the next 20 to 50 years, the risk of permafrost subgrade thawing settlement in the QTEC will be the most significant risk type, and this effect will mainly be distributed in the Kunlun Mountains, Chumar River Plain, Kekexili Mountains, Beiluhe Basin, Tanggula Mountains and intermountain Basins.
... For the QTR and QTH, the roadbed distresses were carefully analyzed, including the study on influencing factors, the type and distribution length of roadbed cooling measures to mitigate permafrost from thawing. For the QTR, a typical section stability analysis of roadbed was conducted where the cooling measures were adopted, including crushed rock embankment and thermosyphon embankment (Zhang et al., 2021). The formation mechanisms of roadbed distress on the QTR and QTH were investigated. ...
... Two mitigation methods were used to prevent the freezing and thawing deformation of permafrost roadbeds. These two mitigation methods are categorized as enhancing ground heat extraction and preventing heat intake [7,8]. Enhanced ground heat extraction methods include the use of crushed rocks, ventilation ducts, and thermosyphons [9]. ...
The frost heave and thaw settlement of subgrades in permafrost regions severely threaten highway safety during repeated freeze–thaw cycles. However, these freeze–thaw cycles are difficult to overcome because of the lack of thermal insulation materials (or structures). To fill this gap, we developed a polyurethane (PU) polymer material with low thermal conductivity and designed a double–layer PU–grouted structure. The water–vapor–thermal coupling governing equations of the grouted subgrade were established. A numerical simulation was conducted using the finite element software COMSOL Multiphysics. Ten-month in-situ tests were conducted on the Qinghai–Tibet Highway from November 2021 to August 2022 to investigate the thermal insulation properties of the grouted subgrade. The results indicated that the PU exhibited excellent thermal insulation performance and considerably reduced the disturbance depth of the air temperature. Freeze and thaw depths were reduced by 0.65 and 1.65 m, respectively. During the freeze period, the surface and deep layers of the subgrade showed a temperature difference of 6 °C due to the upper PU layer, preventing 32.4 % of the liquid water from being frozen. The upper PU layer caused a temperature difference of up to 7 °C between the surface and the deep layers of the subgrade during the thawing period. Water evaporation was prevented by the upper PU layer, and water gathered between the grouted layers, which was defined as the “pot-cover effect.” The pot cover effect significantly reduced the soil temperature and maintained a stable temperature in the deeper subgrade during thawing.
... Frozen ground is widely distributed in the Northern Hemisphere, 1,2 and the distribution of saline-alkali soil 3 overlaps extensively with seasonally frozen ground. Freezing processes in soils are relevant to climate change impacts, 4-6 carbon (including CO 2 and methane) emission, 7,8 engineering practices in cold regions, [9][10][11] and leakage prevention of nuclear contamination. 12 Salinization, on the other hand, is one of the most widespread soil degradation processes that threaten agriculture 13,14 and ecological systems. ...
Sandy saline soils are widely distributed and commonly experience seasonal or long-term freezing, yet the freezing process in these soils is rarely studied. This research utilized in situ X-ray computed tomography (CT) to visualize pore-scale freezing processes in sandy saline soils under various initial water and salt contents. Micron-resolution observations of pore ice and unfrozen water produced new insights into the preferential orientation and grouping of pore ice crystals, intersections between different pore ice crystal groups causing anisotropic behavior, decreasing pore ice crystal size under faster freezing rates, and the formation of interconnected networks of both pore ice and unfrozen water upon freezing. From a thermodynamic perspective, the salt content in the unfrozen liquid is dependent on the local temperature as described by water–salt phase diagram. Furthermore, the local volume ratio between unfrozen water and pore ice reflects the initial salt content and salt mass transfer occurring due to both diffusion and fluid flow processes. This work improves the understanding of complex freezing phenomena in sandy saline soils through high-resolution evidence of crystallization patterns, transformation mechanisms, and coupled heat-mass transfer.
... Researchers have revealed variations in the permafrost in the context of climate warming and wetting . However, most studies have focused on railways, highways, and energy transmission lines, while studies on hydraulic engineering and surface water changes have been limited to permafrost regions (Ma, Niu, and Mu 2012;Mu et al. 2016Mu et al. , 2014Zhang et al. 2021). ...
The outburst of Zonag Lake in 2011 triggered a series of floods in the continuous permafrost region of the hinterland of the Qinghai-Tibet Plateau. This re-distributed the surface water in the basin and caused rapid expansion of the tail lake (Salt Lake). To avoid potential overflow of the expanding Salt Lake, a channel was excavated to drain the lake water into a downstream river. In this study, to investigate the permafrost thermal regime and the surface deformation around the expanding Salt Lake and the channel, in-situ monitoring sections were settled from Salt Lake to the downstream of the channel to obtain the permafrost temperature. Additionally, using small baseline subset interferometric synthetic aperture radar (SBAS-InSAR), the surface deformation around Salt Lake and the channel was measured. The data showed that the ground temperature at the channel was 0.6°C higher than the natural field and the mean subsidence rate around the channel was 1.5 mm/yr higher than that at Salt Lake. These results show that the permafrost temperature in the study area changed considerably with variations in the distance from the lake/channel, and the deformation in the study area was dominated by subsidence.
... Tunnel engineering in the southwestern region of China is generally located in the Qinghai Tibet Plateau and its adjacent areas. This area is compressed by plate tectonics, which results in high tectonic stress (Zhang et al., 2021), and the hydrogeological and geological conditions of the strata are complex. When constructing tunnels, it is inevitable to cause large deformation disasters (Bao et al., 2022). ...
In super deep-buried soft-rock tunnels, significant deformation disasters often accompany high-ground stress. Advanced center drift stress release technology to release some in-situ stress in advanced can effectively solve many problems caused by large deformation. Therefore, based on the Haba Snow Mountain Tunnel in the Lijiang Section of the Yunnan-Tibet Railway, the research on the vertical reasonable position of the advanced center drift is carried out. Using literature research, numerical simulation, and on-site experiments, the deformation of surrounding rock, the stress distribution of support, and the distribution of plastic zone of surrounding rock at different vertical positions of the advanced center drift are studied. The application effect of the advanced center drift is analyzed through on-site monitoring data. The results show that different vertical positions of the advanced center drift have a particular stress-release effect. When the arch top of the advanced center drift is 2 m away from the main tunnel arch top, the stress release effect and support stress are relatively ideal, and the on-site measured tunnel deformation can reduce by an average of 44.52%. The research results can provide reference for the design of advanced center drift in similar projects.
... 近年来，我国在冻土工程建设领域取得了突 出成就，已经建成的大型基础设施包括青藏公路、 青藏铁路、高压输变电线路及中俄输油管道等工 程，标着我国的寒区工程建设能力已经处于国际 领先水平 [1] 。为了加深西部大开发、响应"一带一 路"倡议，在我国乃至世界范围内还将继续加强 基础设施建设，如青藏高速、新藏铁路、京莫高 铁、中俄美加高铁等众多高等级道路也将会逐步 开展，它们同样面临多年冻土问题。 长期以来，在多年冻土地区开展工程建设都 遵 循 着 保 护 低 温 冻 土 、 控 制 高 温 冻 土 融 化 的 原 则 [2] ，为此，国内外学者提出了多种冻土路基结 构，如高填方路基、保温路基、遮阳板路基等被 动保温型结构、块石路基、通风管路基、热棒路 基等主动冷却型结构措施 [3] ，以及多种复合式路基 结构。虽然上述工程措施在一定程度上能够减缓 多年冻土的退化速度，但在长期服役过程中，路 基热害问题仍时有发生 [4] [7−10] 研发了一种太阳能吸附式制 冷管与一种压缩式制冷热管，并通过模型试验测 试了新装置的制冷性能。米维军等 [11−12] 提出了一种 化学吸附式制冷管，通过场地试验证明了新型热 管的制冷性能明显优于普通热管的制冷性能。此 外，有学者将半导体制冷技术应用于保护多年冻 土 [13−14] ...
To improve the problems of permafrost degradation and embankment thermal stability caused by engineering disturbance, the solar direct-drive compression refrigeration apparatus for preventing permafrost degradation was invented based on solar power generation technology and refrigeration technology. The performance of the apparatus was tested by field test, and various working conditions were analyzed by numerical simulation. The results show that the new apparatus can adapt to the severe cold environment in the permafrost region and realize automatic operation. During the operation of the apparatus, the heat flux of the refrigeration tube wall increases with the increase of the total solar radiation, and the average heat flux is −4.1−−6.3 W/m2. Compared with ordinary embankment, refrigeration embankment can significantly improve the permafrost table of the embankment and restrain the temperature rise of permafrost. It can be found that the permafrost table of the embankment will increase with the increase of refrigeration tube length and tube wall heat flux, but it increases first and then decreases with the increase of the embedded depth of the refrigeration tube. The heating rate of ground temperature will decrease with the increase of refrigeration tube length, buried depth, and tube wall heat flux. Finally, based on the grey correlation analysis, it is found that the heat flux of the refrigeration tube wall has the most significant effect on the permafrost table of the embankment, followed by the length of the refrigeration tube, and the embedding depth is the least. The ground temperature rise rate is the most sensitive to the buried depth of the refrigeration pipe, followed by the tube heat flux, and the length of the refrigeration tube is the smallest. Therefore, it is suggested that more significant factors should be preferentially selected for regulation in design and construction.
... The construction and maintenance of infrastructure engineering such as high-speed railways and roadways in special geology regions including but not limited to permafrost Tai et al., 2019;Tai et al., 2020;Zhang et al., 2021), loess (Qi et al., 2017;Xu et al., 2018;Zhou et al. 2019;Sadeghi et al., 2019) and soft soils (Huang et al., 2017;Ngo et al., 2020;Yfantis et al., 2021;Liu et al., 2022), are a challenging task for engineering geologists and geotechnical engineers. Especially, soft soils, as a special geological material extensively existing in coastal cities of southeastern China, bright great challenges to the construction of railway embankments such as the problem of large long-term settlement (Lai et al., 2019;Ersoy et al., 2019;Shan et al., 2022a;Xiao et al., 2023). ...
The excessive displacement of an existing high-speed railway foundation due to the adjacent construction of a railway composite foundation significantly threatens the railway operation safety. In the typical soft soil region of Southeast China, a series of in-situ tests are carried out in this paper to investigate the layered settlement of newly constructed embankment and lateral displacement of an existing high-speed railway foundation induced by the new embankment. A two-dimensional (2D) finite element (FE) model is built to investigate the displacement of stratums and the modified Cam-clay (MCC) model is adopted to pursue the mechanical properties of the silt. Combining the genetic algorithm (GA), a back analysis framework was developed to determine the optimized input parameters of MCC model for silt layer. The results indicate that the displacement of the existing high-speed railway foundation induced by the adjacent construction of a railway embankment decreases with depth and horizontal distance from the newly constructed embankment toe. A hysteresis phenomenon is found in the foundation settlement data during the loading procedure of the embankment. Moreover, the optimized parameters for silt layer (i.e., λ = 0.361, M = 0.828, e0 = 1.347 and k = 0.826×10-8m/s) have the potential for the engineer application in the soft soil region.
... The annual precipitation is between 191 and 485 mm, mainly concentrated in summer (May to October). The elevation fluctuates from north to south [57], and its topographic characteristics are shown in Figure 1. There are four monitoring stations close to this section, namely Golmud, Wudaoliang, Tuotuohe and Anduo meteorological stations. ...
Permafrost areas pose a threat to the safe operation of linear projects such as the Qinghai–Tibet railway due to the repeated alternating effects of frost heaving and thawing settlement of frozen soil in permafrost area. Time series InSAR technology can effectively obtain ground deformation information with an accuracy of up to millimeters. Therefore, it is of great significance to use time series InSAR technology to monitor the deformation of the permafrost section of the Qinghai–Tibet railway. This study uses multi-time InSAR (MT-InSAR) technology to monitor the deformation of the whole section of the Qinghai–Tibet railway, detect the uneven settlement of the railway roadbed in space, and detect the seasonal changes in the roadbed in the time domain. At the same time, the local deformation sections over the years are compared and discussed. The time series deformation monitoring results of the permafrost section Sentinel-1 data in 2020 show that the length of the railway roadbed from Tanggula station to Za’gya Zangbo station (TZ) section is approximately 620 m, the deformation of the east and west sides is uneven, and the average annual deformation difference is 60.68 mm/a. The impact of frozen soil in WangKun station to Budongquan station (WB) section on railway roadbed shows the distribution characteristics of high in the middle and low at both ends, and the maximum annual average settlement can reach −158.46 mm/a. This study shows that the deformation of permafrost varies with different ground layers. The impact of human activities on frozen soil deformation is less than that of topography and hydrothermal conditions. At the same time, the study determined that compared with other sections, the roadbed deformation of TZ and WB sections is more obvious.
... It is well known that the uneven settlement of the embankment seriously affects the smoothness, which causes great difficulties in later operation and maintenance. During the operation of the Qinghai-Tibet Highway (QTH), Qinghai-Tibet Railway (QTR), and Gonghe-Yushu Expressway (GYE), there are many different levels of road diseases, which make it difficult for vehicles to reach the design speed [4,5]. The planned Beijing-Moscow high-speed railway and the China-Russia-America-Canada high-speed railway will pass through ex-tensive permafrost regions. ...
... Because of the viscosity of ice and unfrozen water, frozen soil has significant creep deformation properties under external loading (Ladanyi, 1972). For example, the subgrades of the Qinghai-Tibet highway and even the new constructed Qinghai-Tibet railway projects in permafrost regions have experienced significant uneven subsidence problems (Liu et al., 2002;Wen et al., 2009;Niu et al., 2011;Zhang et al., 2021). Subgrade settlement in permafrost regions is caused by a variety of settlement sources, including melting of ice caused by temperature rising, thawing settlement caused by the freeze-thaw cycle, and creep of frozen soil (Jilin et al., 2007;Ma et al., 2008;Wu et al., 2014). ...
Frozen soil is a kind of composite geotechnical material with significant creep properties. To develop a creep constitutive model that can consider the composite properties and internal microcosmic damage mechanism of frozen soil, it is first conceptualized as a binary medium material containing both bonded elements and frictional elements, and the creep breakage mechanism of frozen soil is analyzed. Then, the relationship between micro-strain and macro-strain is established based on the homogenization theory. The creep constitutive relations of bonded elements and frictional elements are established, respectively, based on the creep breakage mechanism and the fractional calculus theory. In addition, the breakage ratio is defined as a function of creep time. Finally, a new fractional constitutive model with a composite structure is established. The three-dimensional model is also derived to facilitate its extensive application. Reasonable agreement is achieved comparing the model prediction results with the creep experimental results, and the proposed model can accurately capture the creep deformation characteristics of each phase. The results of the parameter sensitivity analysis further demonstrate the applicability of the definition of composite structure for the frozen soil.
... In the middle of this century in the northern hemisphere, a large number of existing engineering facilities will be at high risk in permafrost areas, and the main reason is the degradation of permafrost due to temperature increase [15]. More specifically, the rise of temperature leads to the reduction in the bearing capacity for frozen soil, even more than 75% under unfavorable conditions [35], resulting in an extremely unstable state [18,42], which is finally manifested as engineering issues in embankment [12,33,45], tunnels [49] and slopes [29,38]. ...
In permafrost regions, under the interference of climate warming and human activities, the deformation stability of geological engineering with frozen soil as the medium is directly affected, and the typical ones are the creep characteristics under the influence of temperature and stress level. In order to reveal the internal mechanism of such characteristics, this paper carried out the creep tests of saturated frozen soil under constant/variable temperature conditions, and the following meaningful conclusions are drawn: an increase in temperature and deviatoric stress level leads to an increase in the effect of weakening mechanism on the meso-scale, which cause the creep mechanical behavior transition from a stable state to an unsteady state, and eventually reach a failure state; The creep strain and meso-scale broken law caused by temperature history are important features that affect the creep characteristics at subsequent temperature condition. Furthermore, with the breakage mechanics for geological materials and meso-mechanics theories, the strengthening and weakening mechanisms on the meso-scale under the influence of temperature and stress level (deviatoric stress and confining pressure) were defined and quantitatively described in the creep process, and then, an unified macro-meso creep constitutive model was proposed, which includes stress concentration tensor and breakage ratio. Finally, the creep deformation of saturated frozen soil under constant temperature and variable temperature condition was well predicted. The conclusion of the article can be used to evaluate and predict the long-term deformation stability of geological engineering in cold regions.
... In the middle of this century in the northern hemisphere, a large number of existing engineering facilities will be at high risk in permafrost areas, and the main reason is the degradation of permafrost due to temperature increase [15]. More specifically, the rise of temperature leads to the reduction in the bearing capacity for frozen soil, even more than 75% under unfavorable conditions [35], resulting in an extremely unstable state [18,42], which is finally manifested as engineering issues in embankment [12,33,45], tunnels [49] and slopes [29,38]. ...
In permafrost regions, under the interference of climate warming and human activities, the deformation stability of geological engineering with frozen soil as the medium is directly affected, and the typical ones are the creep characteristics under the influence of temperature and stress level. In order to reveal the internal mechanism of such characteristics, this paper carried out the creep tests of saturated frozen soil under constant/variable temperature conditions, and the following meaningful conclusions are drawn: an increase in temperature and deviatoric stress level leads to an increase in the effect of weakening mechanism on the meso-scale, which cause the creep mechanical behavior transition from a stable state to an unsteady state, and eventually reach a failure state; The creep strain and meso-scale broken law caused by temperature history are important features that affect the creep characteristics at subsequent temperature condition. Furthermore, with the breakage mechanics for geological materials and meso-mechanics theories, the strengthening and weakening mechanisms on the meso-scale under the influence of temperature and stress level (deviatoric stress and confining pressure) were defined and quantitatively described in the creep process, and then, an unified macro–meso creep constitutive model was proposed, which includes stress concentration tensor and breakage ratio. Finally, the creep deformation of saturated frozen soil under constant temperature and variable temperature condition was well predicted. The conclusion of the article can be used to evaluate and predict the long-term deformation stability of geological engineering in cold regions.
... The field investigation along the QTH showed that Budongquan-Beiluhe section was seriously affected by thaw settlement (Chai et al., 2018). In addition, the long-term monitoring along the QTR implied that thaw settlement is the main factor influencing the stability of subgrade (Guo and Sun, 2015;Zhang et al., 2021b). To avoid the potential risk of permafrost degradation to infrastructures, several effective engineering measures have been applied by the QTH and QTR, so as to mitigate the degradation process, e.g. ...
With climate warming, numerous thaw settlements have occurred in the Qinghai-Tibet Plateau (QTP), but their possible distributions and potential risks are still poorly understood. The present study tends to come up with the first hazard data-driven thaw settlement susceptibility map for the QTP, and identify hazard-prone regions for settlement population, main infrastructures, and soil organic carbon (SOC). A well reliable susceptibility map was developed based on 111,510 thaw settlement sites and 12 conditioning factors using random forest (RF) model, logistic regression-based gradient boosting decision tree (GBDT-LR) model, and frequency ratio (FR) model. We found that nearly 120 thousand people, 1653 km of highway, 650 km of railway, and 3.13 Pg of the SOC were located in high and very high susceptible regions, which occupied 34.60% of the permafrost domain in the QTP. Alarmingly, the situation of Qinghai-Tibet Highway (QTH) and Qinghai-Tibet Railway (QTR) in permafrost regions seems more serious, more than 60% of them were located in high and very high susceptible regions. Our results revealed that slope aspect, volume ice content, and active layer thickness contributed significantly to the occurrence of thaw settlement. Compared with similar studies, this research performed better in model construction and accuracy. The results can provide references for decision maker in eco-environment protection and hazard risk management.
... Two-hundred class-I profiles have been randomly generated and are the same quantity for generating class-II, class-C, and class-D profiles. The categorized sites V S30 -depth distribution, with NEHRP provision The profiles are based on geological investigations along the Qinghai-Tibet Railroad (Wang et al. 2009;Su et al. 2016;Tian et al. 2019;Zhang et al. 2021). The quantity of soil layers ranges from 1 to 3, and the lower limit is set to one considering a thin overburden scenario. ...
The horizontal seismic responses in cold regions have not received adequate attentions. In seismic design for frozen ground, computations for unfrozen ground are generally adopted directly. This study uses the Monte Carlo method to verify the applicability of traditional seismic computations in cold regions. Xidatan valley, Kekexili mountain, Chumaerhe plain, and Beiluhe basin along the Qinghai–Tibet railway are selected as the study regions; a series of random soil profiles are generated. Equivalent linear analysis results show that the current Chinese code provides mismatched spectral site amplification estimations at rare seismic intensity level. These estimations can practically be updated by increasing the current seismic motion parameters along the Qinghai–Tibet railway or by amplifying the existing design spectrum with a coefficient. The melting of permafrost layer would increase spectral peak; 70% of the original thickness would result in spectral peak amplification of 120%. Ground temperature model and permafrost dynamic nonlinear performance should be further explored.
... e investigations indicated that the permafrost table beneath the crushed rock embankment in warm permafrost regions was uplifted, but the ground temperature in deep depth experienced a warming trend [46]. Meanwhile, some failures of the measures, including clogged crushed rock layer [47] and damaged thermosyphon [48], pose a challenge to these active cooling measures. During the operation of the QTR, the embankment deformations were mainly due to thawing settlement [17], and the differential settlement was obvious in the embankment-bridge transition section [49]. ...
Characterized by low bearing capacity and high compressibility, warm and ice-rich frozen soil is a kind of problematic soil, which makes the original frozen ground formed by of that unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. With the design and construction of major projects along the Qinghai-Tibet Engineering Corridor (QTEC), such as expressway and airport runway, it is a great challenge to favor the stability of overlying structures by formulating the proper engineering design principles and developing the valid engineering supporting techniques. The investigations carried out in recent years indicated that warm and ice-rich permafrost foundations were widespread, climate warming was significant, and the stability of existing engineering structures was poor, along the QTEC. When the warm and ice-rich frozen ground is used as the foundation soil, the implementation of ground improvement is an alternative measure to enhance the bearing capacity of foundation soil and eliminate the settlement of structures during operation, in order to guarantee the long-term stability of the structures. Based on the key factors determining the physicomechanical properties of frozen soil, an innovative idea of stabilizing the warm and ice-rich frozen soil based on chemical stabilization is proposed in this study, and then, an in situ ground improvement technique is introduced. This study intends to explore the feasibility of ground improvement in warm and ice-rich permafrost regions along the QTEC based on in situ chemical stabilization and provide the technical support and scientific reference to prevent and mitigate the hazards in the construction of major projects in the future.
... Knowledge of the permafrost distribution and its changes are critical for understanding the effects of climate warming and engineering activities on the permafrost environment. Furthermore, the hydrothermal and mechanical stability of permafrost affects the ecology, hydrology, carbon pool, and microbial community and ecological balance (Zhang et al., 2018(Zhang et al., , 2021aMargesin and Collins, 2019;Chen et al., 2020;Jin et al., 2020Jin et al., , 2021aJin et al., , 2021b. The northern Da Xing'anling Mountains in Northeast China is in the discontinuous permafrost zone. ...
The electrical resistivity tomography and vegetation surveys were conducted for investigating the distribution of frozen ground and other engineering geological characteristics at four representative sites (BHP, XFB, WLG, and XAZ) along the China-Russia Crude Oil Pipelines (CRCOPs) I and II. The comprehensive analysis shows that CRCOPs play an important role in forming and connecting supra-permafrost subaerial taliks and in facilitating thermokarst landforms, further accelerating permafrost degradation. The survey results indicate that on 15–29 August 2019, the permafrost base under the CRCOP at the XFB site was 21.5 m in depth, that of WLG site was 21.5 m (32.8 m at the undisturbed sites), and that of XAZ site, 37.3 m; the permafrost table of XFB site was 6.72 m (4.97 m on 20 m away from the pipeline), that of WLG site was 8.64 m (1.94 m at the undisturbed sites), and that of XAZ site was 6.72 and 3.38 m on the southern and northern slopes; the hydrothermal influences of CRCOPs extended horizontally to about 60 m away from the pipelines, but the vertical hydrothermal impacts were largely limited to about 10–15 m in depth at the BHP site in the zone of deep (>1.5 m) seasonal frost. The extent of engineering influences from the pipelines and associated engineering activities in patchy and island permafrost are evidently larger than those in seasonal frost. The sites with substantial changes are found in pipeline foundation soils underlain by warm (> − 1 °C; thermally unstable) and ice-rich permafrost. This study can timely help decision makers mitigate frost hazards in a proactive manner.
Embankment–bridge transition sections (EBTSs) suffer from diverse engineering diseases that have escalated into one of the most severe issues along the Qinghai‐Tibet Railway (QTR). Nevertheless, the causes and mechanisms of engineering diseases in EBTSs remain limited. This study employed a methodological approach to conduct field surveys in the Tuotuo River Basin in the hinterland of the Qinghai‐Tibet Plateau (QTP). Borehole investigations and nuclear magnetic resonance (NMR) techniques accurately determined the permafrost characteristics, enabling the correction of electromagnetic wave velocity and acquisition of resistivity threshold. Ground‐penetrating radar (GPR) and quasi‐3D electrical resistivity tomography (ERT) were combined to indicate permafrost resistivity above 200 Ω‐m. It reveals that the permafrost is relatively stable across a large area on the shaded side, whereas the permafrost degradation is more pronounced on the sunny side, where the maximum active layer thickness (ALT) reaches 5.2 m. Notable permafrost degradation and substantial increases in ALT were observed near the EBTS resulting from heat absorption and thermal erosion of the groundwater. Terrestrial laser scanning (TLS) captured time‐series deformation highlights the specific displacements of the EBTS, demonstrating that the displacement is the rotational behavior of wing walls. The severe heat absorption and groundwater thermal erosion around the EBTS result in permafrost degradation and the expansion of the thawing bulbs to increased structural deformation and even failure. It was shown that permafrost degradation, moisture influence, and heat transfer characteristics are the primary contributing factors to the disease's continued deterioration, and thus reinforcement measures for existing structures need to address these three issues. The mechanisms of disease development revealed in this paper provide new insights into EBTS dynamics for the EBTS design and maintenance in permafrost regions.
Freezing–thawing indices serve as a comprehensive indicator of both the duration of the freezing/thawing periods and the degree of cold and heat in a given region. In-depth analysis of the freezing-thawing indices not only enables the prediction of permafrost distribution and its dynamic changes, but also facilitates the assessment of damage risk to infrastructure under freeze-thaw action. In this paper, the air/ground freezing–thawing indices from 1987 to 2017, based on daily temperature observations from meteorological stations along the China–Nepal Highway (CNH), were calculated, and their spatial and temporal variation patterns were analyzed. The results showed that: (1) Both mean annual air temperature and mean annual ground surface temperature along the CNH fluctuated upward, with climate tendency rates of 0.43 and 0.52°C·(10a)−1, respectively; (2) The number of days with negative air temperature and ground temperature showed fluctuated downward, with change rates of −8.6 and −8.3 d·(10a)−1, respectively; (3) The ranges of air freezing index, air thawing index, ground freezing index, and ground thawing index over the years were 157.05–458.88°C·d, 2034.20–2560.73°C·d, 108.78–396.83°C·d, and 3515.25–4288.67°C·d, respectively. The climate tendency rates were −5.42, 10.22, −6.79, and 12.14°C·d·a−1, respectively, showing a general warming trend; (4) The air freezing index, ground freezing index, and ground thawing index changed abruptly in 1999, 2000, and 2002, respectively, evincing significant changes after 2002. The research results can provide a basis for the risk assessment of freezing–thawing erosion and the prevention and control of permafrost engineering diseases along the CNH.
Gaseous water migration is a crucial factor in the development of frost heaving in coarse-grained fillers. The goal is to study the gaseous water migration and frost heaving characteristics of coarse-grained fillers. Based on the law of light reflection and refraction, Polymer optical fiber (POF) sensors are proposed to monitor the light intensity in the fillers during the freezing process, so that the intrinsic correlation between the light intensity and the phase transition and migration of water can be analyzed. A series of unidirectional experiments was conducted by using a gaseous water migration system alongside POF sensors. The experimental results show that particle size and initial water content profoundly influence the freezing depth and the volume of gaseous water migration. Larger particle sizes and lower initial water contents enhance gaseous water migration. Fine-grained induced early deformation, and the soil skeleton caused continuous frost heaving, with both mutually constraining each other. By harnessing the data from POF sensor monitoring to forge a light intensity-inflow relationship model, it is found that the study could grasp the phase change and gaseous water migration in real-time. The results of gaseous water migration in coarse-grained fillers provided a valuable supplement to traditional frost heaving theory.
In super deep-buried soft-rock tunnels, significant deformation disasters often accompany high-ground stress. Advanced center drift stress release technology to release some in-situ stress in advance can effectively solve many problems caused by large deformation. Therefore, based on the Haba Snow Mountain Tunnel in the Lijiang Section of the Yunnan-Tibet Railway, the research on the vertical reasonable position of the advanced center drift is carried out. Using literature research, numerical simulation, and on-site experiments, the deformation of surrounding rock, the stress distribution of support, and the distribution of the plastic zone of surrounding rock at different vertical positions of the advanced center drift are studied. The application effect of the advanced center drift is analyzed through on-site monitoring data. The results show that different advanced center drift vertical positions have a stress-release particular impact. When the arch top of the advanced center drift is 2 m away from the main tunnel arch top, the stress release effect and support stress are relatively ideal, and the on-site measured tunnel deformation can reduce by an average of 44.52%. The research results can provide a reference for the design of advanced center drift in similar projects.
The heat absorption of the railbed mainly originates from the embankment slope in permafrost regions. A novel ventilated slope (NVS) with a double‐layer convection channel is proposed and verified. By applying this method to the Qinghai–Tibet Railway (QTR), the annual average temperature at the 10 cm depth below the embankment slope surface under NVS was reduced by 4.95°C. The freezing index at the 10 cm depth of NVS was 1.78 times higher than that of the slope without any cooling approaches. The numerical simulation results showed that heat was accumulated for the conventional embankment, while heat was released from the railbed after the application of NVS. With the cooling effect of NVS, the 0°C isotherm would rise above the original natural ground surface in the 2nd year after the embankment construction. A low‐temperature region of −2°C would be observed in the underlying permafrost by the 10th year. The underlying permafrost would remain frozen in the 50th year. This study provides a novel method for protecting the underlying permafrost in permafrost regions.
Affected by climate warming and anthropogenic disturbances, the thermo-mechanical stability of warm and ice-rich frozen ground along the Qinghai-Tibet engineering corridor (QTEC) is continuously decreased, which may delay the construction of major projects in the future. In this study, based on chemical stabilization of warm and ice-rich frozen ground, the soil-cement column (SCC) for ground improvement was recommended to reinforce the foundations in warm and ice-rich permafrost regions. To explore the validity of countermeasures mentioned above, both the original foundation and the composite foundation consisting of SCC with soil temperature of -1.0°C were prepared in the laboratory, and then the plate loading tests were carried out. The laboratory investigations indicated that the bearing capacity of composite foundation consisting of SCC was higher than that of original foundation, and the total deformation of original foundation was greater than that of composite foundation, meaning that overall stability of foundation with warm and ice-rich frozen soil can be improved by SCC installation. Meanwhile, a numerical model considering the interface interaction between frozen soil and SCC was established for interpretating the bearing mechanism of composite foundation. The numerical investigations revealed that the SCC within composite foundation was responsible for the more applied load, and the applied load can be delivered to deeper zone in depth due to the SCC installation, which was favorable for improving the bearing characteristic of composite foundation. The investigations provide the valuable guideline for the choice of engineering supporting techniques to major projects within the QTEC.
The Qinghai-Tibet Railway has been operating safely for 16 years in the permafrost zone and the railroad subgrade is generally stable by adopting the cooling roadbed techniques. However, settlement caused by the degradation of subgrade permafrost in the embankment-bridge transition sections (EBTS) is one of the most representative and severe distresses. A field survey on 440 bridges (including 880 EBTSs) was carried out employing terrestrial laser scanning and ground-penetrating radar for comprehensively assessing all EBTSs in the permafrost zone. The results show that the types of distresses of EBTSs were differential settlement, upheaval mounds of the protection-cone slopes, subsidence of the protection-cone slopes, surface cracks of the protection cones and longitudinal and transverse dislocation of the wing walls. The occurrence rates of these distresses were 78.93, 3.47, 11.56, 3.36, 21.18 and 4.56%, respectively. The most serious problem was differential settlement, and the average differential settlement amount (ADSA) was 15.3 cm. Furthermore, the relationships between differential settlement and 11 influencing factors were examined. The results indicate that ADSA is greater on the northern side of a bridge than on the southern side and on the sunny slope than on the shady slope. It is also greater in the high-temperature permafrost region than in the low-temperature permafrost region and in the high-ice content area than in the low-ice content area. The EBTSs are more influenced by ice content than by ground temperature. The ADSA increases when the embankment height increases, the particle size of subgrade soil decreases and the surface vegetation cover decreases.
Effectively evaluating high-embankment deformation and stability is important for heavy-haul railway safety. An improved extension model with an attribute reduction algorithm was proposed for the comprehensive evaluation method. First, a hierarchical evaluation system for high embankments in heavy-haul railways was established using the attribute reduction algorithm, which includes the principal component analysis, maximum information coefficient, coefficient of variation, and improved Dempster-Shafer evidence theory. Furthermore, the improved extension model was used to evaluate high-embankment performance in heavy-haul railways. In this improved extension model, the combination weighting method, an asymmetric proximity function, and the maximum membership principle effectiveness verification were used. Finally, three high embankments in a Chinese heavy-haul railway were studied. The results illustrate that the main influencing factors for high-embankment performance in a heavy-haul railway are annual rainfall, annual temperature, and 21 other indicators. The performance of the three embankments is level III (ordinary), level II (fine), and level III (ordinary), respectively, indicating that these embankments have generally unfavourable performance. The three embankments’ performance matches field measurements, and the proposed method outperforms the Fuzzy-AHP method, cloud model, and gray relational analysis. This study demonstrates the feasibility of the proposed method in assessing the high-embankment performance under heavy axle loads.
It is proposed to build a high-speed railway through the China‒Mongolia‒Russia Economic Corridor (CMREC) which runs from Beijing to Moscow via Mongolia. However, the frozen ground in this corridor has great impacts on the infrastructure stability, especially under the background of climate warming and permafrost degradation. Based on the Bayesian Network Model (BNM), this study evaluates the suitability for engineering construction in the CMREC, by using 21 factors in five aspects of terrain, climate, ecology, soil, and frozen-ground thermal stability. The results showed that the corridor of Mongolia's Gobi and Inner Mongolia in China is suitable for engineering construction, and the corridor in Amur, Russia near the northern part of Northeast China is also suitable due to cold and stable permafrost overlaying by a thin active layer. However, the corridor near Petropavlovsk in Kazakhstan and Omsk in Russia is not suitable for engineering construction because of low freezing index and ecological vulnerability. Furthermore, the sensitivity analysis of influence factors indicates that the thermal stability of frozen ground has the greatest impact on the suitability of engineering construction. These conclusions can provide a reference basis for the future engineering planning, construction and risk assessment.
Serious track settlement of high-speed railways can be induced as the groundwater table in a normal geologic environment is uplifted or partial embankment is submerged following extensive rainfall. However, the settlement development of ballastless track as well as the internal mechanisms underlying this process remains unclear, which becomes more urgent with the frequent occurrence of extreme weather events. In this study, a full-scale model test on the widespread high-speed railway foundation was therefore conducted under sequentially elevated water tables, coupled with millions of axle loads at train speeds of 108 km/h, 216 km/h, and 360 km/h. The results obtained indicate that overall settlement converged on 4.1 mm under a normal water table, even subjected to a long-term train load at 360 km/h. Indeed, given submerged subsoil conditions, this value increased by 5.0 mm due to temporary increases in pore pressure in subsoil and stabilized at 9.8 mm after drainage route formation. These results suggest plastic shakedown behavior. As the subgrade was submerged, pore pressure in the subsoil as well as overall foundation settlement increased continuously under 108 km/h and 216 km/h, presenting plastic creep responses. Abrupt increases in pore pressure were induced under 360 km/h, resulting in rapid development of overall settlement up to 70.0 mm. This implied that foundations stepped into incremental collapse states. A settlement prediction approach that considers water table rises is therefore proposed; a critical water table of 0.973 m beneath the subsoil surface is therefore necessary for safe operations at speeds lower than 360 km/h. As a typical high-speed railway foundation, the obtained results will be useful references for water table warning under similar geologic conditions.
Railway track design and maintenance researchers have been pursuing reliable methods for predicting the long-term performance of the Qinghai-Tibet railway (QTR) subgrade. Based on theoretical analysis, numerical simulation, field monitoring and laboratory tests, this paper studied the train-induced vibration response characteristics of the Beiluhe subgrade of the QTR to evaluate the impact of railway vibration loads on the ice-rich permafrost layer. The results show that increasing the embankment height can significantly reduce the additional dynamic stress of the ice-rich permafrost layer. Moreover, increasing the mean annual ground temperature (MAGT) and decreasing the embankment height will aggravate permafrost table vibration-induced subsidence. This study also analysed the relationships between the train-induced permafrost table vibration subsidence and the MAGT, the ice-rich permafrost layer thickness and the embankment height and predicted the permafrost table vibration subsidence in the DK1136 test section under different global warming conditions. The analyses and prediction demonstrate that the appropriate embankment height of the DK1136 section is 3–3.5 m, and the application of engineering measures for actively cooling the permafrost foundations is the best choice for reducing vibration-induced subsidence, thawing settlement and compression deformation.
Warm permafrost is a challenging geological material for infrastructure engineering. This study presents the observed damage, ground temperature, and settlement at varying depths from three-year continuous monitoring of two selected highway embankment segments along the Qinghai-Tibet Highway in warm permafrost areas, including one conventional embankment and the other with heat pipes on the sunny slope side. Field monitoring data reveal that the embankment settlement mainly results from thaw consolidation of warm permafrost, and the permafrost table beneath a conventional embankment is concave-shaped due to the polythermal effects of asphalt pavement. In contrast, the permafrost table underneath the embankment equipped with heat pipes on the sunny side is convex-shaped due to heat pipes' cooling effects. The different causes of longitudinal cracks on the two embankment surfaces were uncovered based on field observed data. Results of coupled hydro-thermal-mechanical model simulation considering climate warming show that while the configurations of heat pipes on both sides of the embankment can generally ensure the long-term thermal stability and limit the differential settlement across the road surface, the one with slanted heat pipes delivers the best performance and is recommended for future applications. Results from this study, including field monitoring data and recommended heat pipe configuration, will be of value for the construction and maintenance of transportation infrastructure in warm permafrost regions.
A key issue in ensuring the stability of transportation infrastructure in permafrost regions of the Qinghai–Tibet Plateau (QTP) is to prevent the degradation of the underlying permafrost. Therefore, several cooling methods (such as sun sheds, duct-ventilated embankment, thermosyphon, crushed-rock embankment, and dry bridge) have been developed to stabilize the underlying permafrost and mitigate thaw settlement. In this study, considering climate warming and engineering geologic conditions, a necessity model of cooling methods for transportation infrastructure was proposed. The application features of cooling methods along the Qinghai–Tibet Railway (QTR) in permafrost regions were systematically and comprehensively summarized to validate the model accuracy. The results indicated that the model has satisfactory performance and can determine the necessity index (NI) of cooling methods in a certain area. Based on the NI values, convenient application criteria for cooling methods were proposed. Specifically, the transportation infrastructure can be constructed without cooling methods in regions where the NI is less than 1.088. The results indicated that approximately 97% of the regions (NI < 1.088) in the study area are located in talik and low-temperature and ice-poor permafrost regions. Therefore, NI = 1.088 was determined to be a reasonable boundary value for deciding whether to apply cooling methods. Finally, the reliability of the criteria was validated by analyzing the settlement data of six typical embankment sections. This model can improve the reasonableness of the decision-making process of cooling method selection during the design and construction of transportation infrastructure, not only in the Qinghai–Tibet engineering corridor but also in a wide region of the QTP.
A new work-flow is proposed to unify the way the community shares Logistic Regression results for landslide susceptibility purposes. Although Logistic Regression models and methods have been widely used in geomorphology for several decades, no standards for presenting results in a consistent way have been adopted; most
papers report parameters with different units and interpretations, therefore limiting potential meta-analytic applications. We first summarize the major differences in the geomorphological literature and then investigate each one proposing current best practices and few methodological developments. The latter is mainly represented
by a widely used approach in statistics for simultaneous parameter estimation and variable selection in generalized linear models, namely the Least Absolute Shrinkage Selection Operator (LASSO). The North-easternmost sector of Sicily (Italy) is chosen as a straightforward example with well exposed debris flows induced by extreme rainfall.
In the context of climate warming, damage to road pavements and embankments in permafrost regions caused by thawing of underlying permafrost severely reduces the serviceability of roads. In this study, 10 types of asphalt pavement damage were measured every kilometer along the Qinghai–Tibet Highway (QTH), from Kunlun Mountain to Tonggula Mountain (approximately 440 km in permafrost regions). Based on observed data and embankment geometry along the QTH, and information about the characteristics of the permafrost, aspects of pavement deterioration are analyzed and discussed. The three most common forms of pavement damage in the permafrost regions are transverse cracking (TC), potholes, and longitudinal cracking (LC), observed in 87, 64, and 57% of the study section, respectively. About half of the damaged pavement was also affected by block cracking (BC) and alligator cracking (AC), in addition to LC and TC. Results also showed that pavement damage in the degrading permafrost regions was closely related to the underlying permafrost characteristics and embankment geometry. Damage from settlement and patching were more severe in sections with high ice content than low ice content. All the above forms of damage increase exponentially with higher underlying permafrost temperatures. Because of the significant thermal effects of sunlit/shaded slopes, BC, LC, and TC cracking is closely related to roadway orientation, with the most severe cracking damage observed in roads oriented approximately east to west (E–W). Also, more LC was seen in sections of greater embankment thickness, which exacerbates the sunlit/shaded thermal effect.
In Transbaikal and in the adjacent territories including China for the last 20 years was activated the building of railroad and highways. Experience of development anti-deformation measures for the Russian and Chinese railroads and highways with utilization active methods of strengthening of the railway embankment on ice-rich permafrost is illuminated. New technical solutions anti-frost heaving devices for contact-line and airline supports on permafrost and a deep seasonal freezing of the soils, providing decrease of forces of a regulation seasonally-thawed soils with a lateral area of a support and reduction of their power and humidity are defined also at simultaneous magnifying of pinching down action of the transmission tower footing by upheaval of a roofing of permafrost by means of the taken out a patent for modes; experience of design and the installation new anti-frost heaving devices is featured at renovation of an overhead contact system Transbaikal railroad.
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.
This paper reviews the effectiveness and costs of strategies to improve roadbed stability in permafrost regions, based on a synthesis of literature findings. Roadbeds in permafrost regions experience instability when the embankment loading and its heat absorption properties degrade the permafrost foundation. A variety of engineering strategies are used to mitigate this effect. The review summarizes the rationale, effectiveness, and costs of four types of strategies, namely those that control roadbed thawing, cool the roadbed, insulate the roadbed, and reduce roadbed fill weight. The literature reveals that strategies to control roadbed thawing, insulate the roadbed, or reduce roadbed fill weight do not reverse the long-term degradation of permafrost foundations. Strategies that cool the roadbed by implementing air convection embankments, ventilation ducts, thermosiphons, heat drains, or combinations of these are effective in reducing embankment temperatures and stabilizing the roadbed. Costs vary by geographic and climatic conditions and the proximity of materials to the construction site. Reported data suggest that conducting normal maintenance is less expensive than implementing roadbed cooling strategies, but maintaining serviceability may not be feasible.
It is anticipated that an increase in Arctic rainfall will have significant impacts on the geomorphology of permafrost landscapes. Field observations, remote sensing and historical climate data were used to investigate the drivers, processes and feedbacks that perpetuate the growth of large retrogressive thaw slumps. These “mega slumps” (5 to 40 ha) are now common in formerly glaciated, fluvially incised, ice-cored terrain of the Peel Plateau, NW Canada. Individual thaw slumps can persist for decades and their enlargement due to ground ice thaw can displace up to 10- 6 m3 of materials from slopes to valley bottoms reconfiguring slope morphology and drainage networks. Analyses of Landsat images (1985 to 2011) indicate that the number and size of active slumps and debris tongue deposits has increased significantly with the recent intensification of rainfall. The analyses of high resolution climatic and photographic time-series for summers 2010 and 2012 shows strong linkages amongst temperature, precipitation and the downslope sediment flux from active slumps. Ground ice thaw supplies meltwater and sediments to the slump scar zone and drives diurnal pulses of surficial flow. Coherence in the timing of down valley debris tongue deposition and fine-scaled observations of sediment flux indicate that heavy rainfall stimulates major mass flow events. Evacuation of sediments from the slump scar zone can help to maintain a headwall of exposed ground ice, perpetuating slump growth and leading to larger disturbances. The development of debris tongue deposits divert streams and increase thermoerosion to initiate adjacent slumps. We conclude that higher rainfall can intensify thaw slump activity and rapidly alter the slope-sediment cascade in regions of ice-cored glaciogenic deposits.
With recent climatic warming and enhanced human activities, slope failures related to permafrost degradation are widespread along the Qinghai–Tibet Engineering Corridor. Assessment and mapping of the slope failures are necessary to mitigate hazards and plan engineering activities. According to our field investigations, the occurrence of slope failures is mainly controlled by the slope gradient, ground-ice content, permafrost temperatures, surficial deposits, and slope aspect. Modeling conducted in ArcGIS™ was used to produce a slope failure susceptibility map for a representative region along the Qinghai–Tibet Railway from Wudaoliang to Fenghuo Mountain Pass. The study region was divided into four classes based on slope failure susceptibility: (1) unlikely, (2) low, (3) moderate, and (4) high. Areas classified as unlikely accounted for 10.76 % of the study region, while low susceptibility areas comprised 44.51 %. The moderate and high susceptibility zones comprised 21.79 and 22.94 %, respectively. The actual distribution of slope failures in the region was consistent with the modeled results, which demonstrates the utility of the assessment method for future hazard management and engineering planning.
Climate change and engineering activities are the leading causes of permafrost temperature increase, active layer thickening, and ground-ice thaw, which trigger changes in the engineering stability of embankments. Based on the important research advances on permafrost changes and frozen soil engineering in Qinghai-Xizang Plateau, the changes in permafrost temperature and active layer thickness, their relationships with climate factors, the response process of engineering activities on permafrost, dynamic change of engineering stability of Qinghai-Xizang Railway, and the cooling mechanism and process of crushed-rock layers are discussed using the monitoring data of permafrost and embankment deformation. Finally, solutions to the key scientific problems of frozen soil engineering under climate change are proposed.
Seasonal variation of diurnal cloud activity (abbreviated DCA) over the Tibetan Plateau throughout the year is examined using 3-hourly geostationary meteorological satellite (GMS) data for 6-years (1989-1994). The DCA shows two distinct variance maxima in the seasonal cycle. One is in spring (pre-monsoon season), and the other is in the summer monsoon season. The DCA begins in late January, and reaches its maximum from March through April. The active DCA extends over almost the whole of the plateau, especially over the southern part (around 30°N, 90°E) and the zonally oriented belt between 35°N, 80°E and 31°N, 102°E. A short interval between the two active DCAs is found around late May to early June. The DCA starts again over the southeastern region of the plateau (centered around 30°N, 101°E) in June and moves up to the southern region. From July to August, the DCA is most active over the southern region (around 30°N, 86°E). After September, the active DCA retreats to the southeastern region. In both spring and summer, the amplitude of the DCA fluctuates on intra-seasonal time scales. In the active period of the DCA in spring, corresponding to the meandering of the upper-level mid-latitude westerly to the south of the plateau with a trough, the cold air mass at the upper-level is clarly seen over the plateau and weak wind speed is observed through the plateau troposphere. This atmospheric structure and a heating of the lower atmosphere during daytime are likely to be responsible for the enhancement of the DCA in spring. In contrast, during summer monsoon season, the increase of humidity and temperature are identified at the lower atmosphere over the plateau, associated with a humid and warm air intrusion from the South Asian monsoon area into the lower atmosphere over the plateau and precipitation due to active convection. This indicates an increase of the instability for moist convection. These features of the atmospheric circulation and the surface heating during daytime induce active moist convection. Corresponding to the enhanced DCA over the southern part of the plateau, the center of the Tibetan high is located over there. A possible mechanism for the intraseasonal variability of the DCA associated with that of the upper-level atmospheric circulation is also discussed.
The present distribution of permafrost on the Qinghai-Xizang (Tibet)
Plateau (QTP) is largely a relict of the permafrost formed during the
late Pleistocene. It has been degrading and shrinking in areal extent
under the fluctuating climates, with a general trend of warming, during
the Holocene. The major criteria for the occurrence of relict permafrost
include the remnants of ancient buried permafrost, relict permafrost
tables, thawed sandwiches (taliks), thick-layered ground ice, and
periglacial phenomena such as pingo scars, cryoturbations, primary sand
and clayey silt wedges, ice wedge casts, aeolian sand dunes and loesses,
thick layers of peat, and humic soils. On the basis of 14C
dating of soils, comprehensive analyses, and comparisons of the
spatiotemporal distribution of relict and modern permafrost and
periglacial phenomena, the evolution of permafrost and periglacial
environments since the late Pleistocene was divided into seven stages:
(1) the cold period at the end of the late Pleistocene (35,000 to 10,800
years B.P.); (2) the period of significant climatic change during the
early Holocene (10,800 to ˜8500-7000 years B.P.), (3) the
Megathermal period in the middle Holocene (˜8500-7000 to
˜4000-3000 years B.P.), (4) the cold period in the late Holocene
(˜4000-3000 to 1000 years B.P.), (5) the warm period in the later
Holocene (1000 to 500 years B.P.), (6) the Little Ice Age (500 to 100
years B.P.), and (7) the recent warming period (100 years B.P. to
present). The conditions for permafrost development, distribution, and
the paleoclimates and paleoenvironments are discussed for each stage.
Air and ground temperatures are important factors contributing to land and atmosphere processes as well as ecosystem dynamics. This paper presents a simple model for simulating ground temperature from air temperature in the permafrost regions on the Qinghai-Tibetan Plateau (QTP). The model takes hysteresis between daily air temperature and ground temperature into consideration as well as exponential and linear functions for annual average ground temperatures at different depths. Results indicate an evident hysteresis in ground temperature with increasing depth. By taking hysteresis into account, the developed model provides improved daily ground temperature estimates compared to those obtain from the original linear regression, at Xidatan (site QT09) and Kunlun Pass (site CN06) in the permafrost regions on the QTP, with an average root mean square error (RMSE), normalized standard error (NSEE), and mean absolute error (MAE) of 1.12 °C, 0.41, and 0.84 °C for QT09, and 1.41 °C, 0.29 and 1.10 °C for CN06, respectively, at all depths. The results indicate that the model that takes hysteresis into account provides monthly ground temperatures that are closest to field observations, with an average RMSE, NSEE, and MAE of 0.63 °C, 0.24, and 0.50 °C, respectively, at QT09 site and 0.92 °C, 0.18 and 0.63 °C, respectively, at CN06 site. In addition, the simulation accuracy of the average annual ground temperature is significantly improved by using the combined exponential and linear model, and this is particularly relevant when drilling boreholes at great depths in permafrost regions. Therefore, these models provide a useful and simple method for simulating ground temperature and modeling permafrost changes under global warming conditions.
The Himalayan range is one of the most tectonically active mountain ranges on Earth. The Jilong Valley is a deeply-dissected canyon in the Chinese Himalayas in Tibet, and in this valley, landslide hazard and risk have increased significantly in response to active crustal movements, intense rainfall and ever-increasing human interference. Landslide susceptibility assessment in the valley is fundamental for risk mitigation and to inform land use and planning but remains a challenge owing to the inaccessible high altitude and incomplete landslide inventory. In addition, because of sustained glacial erosion, weathering, and denudation, there is considerable uncertainty in the use of remote sensing interpretation of landslides in high-altitude terrain. In this paper, therefore, a systematic approach for landslide susceptibility assessment is proposed, combining the interpretations from remotely sensed dataset and both heuristic and statistical susceptibility models to overcome the problem of the limited spatial coverage of landslide data and uncertainty in landslide interpretation. The main steps include: 1) landslide field investigation and interpretation and the compilation of a preliminary landslide inventory, including certain and probable landslides, 2) knowledge-driven identification of landslide-prone areas based on the heuristic model, 3) classification and quantification of the uncertainty of probable landslides through heuristic landslide-prone areas mapping and the production of a revised landslide inventory, and 4) data-driven susceptibility assessment using a statistical model. In the statistical model, the landslide samples have multivalent dependent variables between 0 and 1. Therefore, a multinomial statistical classifier and multiclass Receiver Operation Characteristic curves are needed for model calibration and validation. The statistical susceptibility mapping showed good performance in the study area, with an average AUC of 0.867, which is a significant improvement over the heuristic model. The methodology presented can be used for landslide susceptibility mapping in data-scarce environments, not only in the Himalayan region but also in other mountainous areas where there is a lack of data on past landslide occurrences.
Surface water is an important local factor in engineering geological conditions in permafrost regions. In this paper, the impacts of surface water ponding on the long-term thermal and settlement characteristics of an air convection embankment (ACE) were investigated based on 13 years of data records from field observations along the Qinghai-Tibet Railway (QTR). The time series of the ground temperatures and the settlement of two ACEs with and without adjacent surface water ponding were investigated and compared. The results indicated that surface water ponding could significantly affect the thermal performance of the ACE. Without surface water ponding, the ACE showed a satisfactory cooling effect; the underlying permafrost table rose, and the shallow permafrost layer cooled significantly after construction of the embankment. However, with surface water ponding, the great heat capacity and latent heat of the ponded water and related capillary action impeded the thermal interaction between the ACE and the underlying permafrost. Before the drainage of the ponded water, no permafrost cooling occurred beneath the embankment. The settlement of the two ACEs also differed significantly. The creep of the ice-rich permafrost layer immediately beneath the permafrost table was inferred as the main contribution of the settlement. The temperature of the layer was the main factor determining the rate of settlement. The results can help the hydro-thermal analysis of engineering foundations built over permafrost and provide a reference for embankment construction and maintenance in permafrost regions with rich surface water.
The structural functionality of roads and railways in warm permafrost regions is influenced by both physical and mechanical processes at work within the underlying subgrade. This paper uses ten-years worth of monitoring data to examine the thermal regimes and deformation behaviors of three different types of crushed-rock embankments employed in the construction of the Qinghai-Tibet Railway, which is located in a warm permafrost region of the Tibetan Plateau, China. More specifically, the efficiency of U-shaped crushed-rock, crushed-rock revetment, and crushed-rock basement embankments in stabilizing permafrost temperature is evaluated with consideration to the permafrost table, ground temperature, and mean annual ground temperature. Then, deformation laws in the three embankments were analyzed. Finally, deformation characteristics and sources for general subgrade are discussed and summarized on the basis of monitoring data and previous research. Results show the permafrost table of each of the three crushed-rock embankments to be higher than that of the natural ground at all times, and that the underlying permafrost warms with time regardless of the type of embankment employed. The deformation characteristics of general subgrade in permafrost regions are determined to be non-uniform and persistent. Furthermore, U-shaped crushed-rock embankment out-performed both crushed-rock revetment embankment and crushed-rock basement embankment in terms of cooling capacity and ability to weaken the sunny-shady slope effect. These findings stand to provide important guidance for understanding the deformation mechanisms of subgrade in warm permafrost regions, as well as for improving Qinghai-Tibet Railway embankment quality and operational safety.
Understanding the long‐term role of cooling the underlying permafrost of the crushed rock structure embankment (CRSE) along the Qinghai–Xizang Railway (QXR) is crucial for the railway's safe operation. The thermal regime of the permafrost under the CRSE is analyzed here using monitoring data of soil temperature from 2005 to 2015. The results show that the CRSE plays an important long‐term role in cooling the underlying permafrost under the present climate change conditions; however, different types of CRSEs have different cooling effects. A U‐shaped crushed rock embankment and a crushed rock berm embankment with debris rock revetment can maintain the cooling of the permafrost underlying the embankment under a future climate warming of 1.0°C. Moreover, under an increase in air temperature of 0.5°C, a crushed‐based rock embankment and a crushed rock revetment embankment can maintain the cooling of the underlying permafrost when its mean annual ground temperature is below −1.0°C. The long‐term role of cooling the underlying permafrost of CRSEs indicates that the QXR must use reinforcing engineering techniques to ensure its safe operation and adaptation to a temperature increase of 1.5°C.
In permafrost zones, the ground thermal regime beneath and around foundations is of great importance to long-term stability and integrity of engineering infrastructures. In this study, ground temperatures beneath and around embankments of the Qinghai-Tibet Highway (QTH) and the Qinghai-Tibet Railway (QTR) were observed at two profiles in continuous permafrost zones on the Qinghai-Tibet Plateau. The lateral thermal influences of the embankments on natural ground in the vicinity were analyzed based on the field observed data. The results indicated that the lateral thermal influence of the QTH and QTR embankments on shallow ground in the vicinity was very slight. The permafrost table depth or freeze-thaw process in the shallow ground near the embankments was mainly determined by the ground surface conditions. Different from the case of shallow ground, the lateral thermal influence of the QTH embankment on the permafrost in the vicinity was significant. Based on the permafrost temperature distribution at −10 m depth, the scopes of the lateral thermal influence of the QTH embankment calculated from the embankment shoulder were as much as 30–40 m at the two observation profiles. Whereas, the lateral thermal influence of the QTR embankment on the permafrost in the vicinity was slight. Because the QTR was constructed using cooling method of crushed rock embankment at the two profiles, the underlying permafrost either maintained well in thermal regime or experienced a slight cooling. The factors affecting the scope of the lateral thermal influences of embankments on permafrost in the vicinity were discussed at the end of the paper, as well as the related mitigation method. This study provides information that could aid engineering design of linear transportation projects and the assessment of environmental impacts in permafrost zones.
Warm permafrost sites such as those extensively existing on the Qinghai-Tibet Plateau present a challenging geological environment for infrastructure engineering. A reliable drainage system is crucial for long-term stability of railway embankment in such sites. This paper presents a case study of the drainage trench along the Qinghai-Tibet railway embankment. The damage patterns to the precast U-shaped concrete lining originally installed in 2008 is described. A coupled thermal-hydro-mechanical finite element model and its results including temperature and stress distributions during ground freezing are presented. Parametric study was also conducted to assess the sensitivity of these results to soil water content and the stiffness of the U-shaped concrete lining. Based on the modeling results, a new design including a coarse-grained transition layer and impermeable geotextile was proposed for field experiment and its field performance six years after its construction is presented. The damage to the original trench was characterized by disjointed lining segments and extensive longitudinal cracks mostly located below the mid-height of the linings. Factors contributing to the damage include challenging construction conditions, uneven thaw settlement, and frost heave stress. Modeling results show that significant horizontal frost heave stress can develop on the outside surface of the U-shaped lining and hence results in large tensile stress at the outside edge of the U-shaped lining. The tensile stress may exceed the lower bound of the concrete flexural strength and induce longitudinal cracks at depths below the mid-height of the lining, which agrees well with field observation. Field performance of the new trench design during a period of six years shows that the improved design performed well and can be adopted for future engineering practice in similar challenging geology conditions.
In this study, Sentinel-2A (S-2A) Multi-Spectral Instrument (MSI) Level 1C (L1C) products are used for identification and mapping of rock glaciers within a transect under observation in Sikkim Himalayas. The mapped rock glaciers were classified on the basis of their activity (intact or relict) and their origin (glacier-derived or talus-derived). Logistic regression models were applied to calculate the probability of permafrost distribution within transect under observation. We observed that freely available high resolution S-2A MSI L1C products are a valuable addition to the already existing freely available high resolution satellite images that can be exploited to study rock glaciers in Himalayan region. The distribution of rock glaciers in Sikkim Himalayas is found to be strongly controlled by elevation and aspect. Topoclimatic conditions above 5000 m a.s.l. are favourable for the presence of permafrost in Sikkim Himalayas. More glacier-derived rock glaciers than talus-derived rock glaciers were observed within transect under observation. Outputs from logistic regression models were capable to reasonably estimate the spatially-distributed probability of permafrost occurrence in the region. However, outputs from these models depended upon the selection of the initiation line location points of rock glaciers and topoclimatic and topographic variables used as predictors for model computation. Based on probability distribution maps, more than 60% (>800 km ² ) area of transect under observation could contain permafrost. This high areal abundance of permafrost in Sikkim Himalayas suggests increased risks of thawing permafrost under the influence of climate warming in future.
The thermal regime of permafrost in the rugged topography on parts of the Qinghai-Tibet Plateau (QTP) remains ambiguous, due to general inaccessibility and inconvenient investigations with geophysical prospecting. While the relatively easy implementations of monitoring ground surface temperature (GST) may facilitate the investigations
of permafrost thermal state. Here, surface freezing and thawing and the relationship between GST and permafrost temperature are investigated in the Bayan Har Mountains, NE QTP on the basis of 22 monitoring sites. Results demonstrate that, unlike the air temperature (Ta) mainly controlled by elevation, the GST is complicately influenced by elevation and the surface characteristics, such as vegetation, local soil textures, as well as the exposure to solar radiation. Mean annual GST (MAGST) ranges from 1.1 °C to−3.1 °C and is averaged at −0.8 °C. MAGST generally decreases at a lapse rate of 1.1 °C/100m in relation to elevation. Surface freezing and thawing processes depend on topography and local surface characteristics. The onset of unstable thawing, stable thawing, unstable freezing, and stable freezing are averaged at 6 April 2015, 15 May 2015, 14 October 2015, and 21 October 2015. Based on the relationship between MAGST and the ground temperature at the depth of zero annual amplitude, GST likely serves as a reliable indicator of the thermal state of permafrost. For the 22 sites, it is estimated that the lowest TZAA of permafrost is −3.4 °C and the thickest permafrost is 106.2 m. However, detailed investigations of subsurface characteristics are indispensable for the accurate inference of permafrost.
This article presents the results of geocryological investigations conducted in the ice-rich permafrost section of the railway during the geotechnical exploration, design and construction stages, as well as prior to its permanent operation.
Changes in the thermal regime of the subgrade and embankment soils have been quantified associated with the wide use of thermosyphons and insulation materials. The observations indicate rising of the permafrost table and cooling of the subgrade under high and low embankments, and active-layer deepening and ground temperature warming on the right-of-way along the railroad. Where a zero-slope fill is placed with removal of the active layer, perennial thaw bulbs have developed in the subsoil. Degradation of ice-rich permafrost is observed on the cut slopes and ditches in the cut sections. Thermosyphons on the berms in combination with Penoplex insulation have shown a cooling effect on the subgrade and permafrost table. Overhanging snow sheds on the embankment slopes have also proved to be beneficial in reducing subgrade temperatures.
Crushed-rock revetment embankments (CRRE) were the most commonly used structure in the construction of the Qinghai–Tibet Railway, and also is a main strengthening measure at the later period's maintenance. Numerical and short-time field monitoring results have confirmed the cooling effects of CRRE, but studies regarding the long-term embankment thermal regime and deformation are still required to fully evaluate their performance. This paper discusses the cooling effects and embankment settlement of a CRRE at the Qinghai–Tibet Railway by examining the ground temperatures and embankment deformation between the years of 2003 and 2014. The results indicate that the crushed-rock layer has lowered the permafrost temperatures beneath the embankment and promoted permafrost aggradation. The estimated annual heat budget of the permafrost beneath the embankment was negative during the studied time period, indicating the sustained cooling performance of the CRRE. Furthermore, although the embankment shoulders experienced settlement, this settlement was smaller than that of a traditional embankment with normal gravel soil fills. This study confirms the utility of the CRRE as an effective design and maintenance measure for roadbeds in warm permafrost regions.
Seepage-induced internal instability is a phenomenon whereby fine particles are transported from a non-plastic soil. A distinction can readily be made between a washed-out soil structure that remains intact and one in which some form of destruction or collapse of the structure accompanies the migration of fine particles. The three variables of a measured value of mass loss, a measured value of volume change and a value of change in hydraulic conductivity, deduced from measurements of hydraulic gradient and flow rate, are sufficient to quantify, and hence distinguish between, seepage- induced internal instability phenomena. The term ‘suffusion’ is advocated to describe the non- destructive response, which may be quantified by a mass loss, no change in volume and an increase in hydraulic conductivity. The term ‘suffosion’ is recommended to describe the instability phenomenon whereby the transport of fine particles by seepage flow is accompanied by a collapse of the soil structure. Accordingly, this distinct internal instability phenomenon may be quantified by a mass loss, a volumetric contraction and a change in hydraulic conductivity.
Coupled strengthening measures of ripped-rock (RR) revetment and two-phase closed thermosyphons (TCPTs), referred to as CRRTs, have proved to be effective in solving the thaw-induced problems in engineering constructions in permafrost regions. However, one of the key issues is related to the effectiveness of the current CRRT systems in the long term. In this paper, a coupled strengthening model with a CRRT is established to rebuild and forecast the geo-temperature distribution before and after the reinforcement. The geothermal conditions are recorded for three cases: a heat insulating embankment reinforced with RRs and vertically implemented TPCTs, a heat insulating embankment and general embankment reinforced with CRRT in which the TCPTs are vertically implemented, and a heat insulating embankment and general embankment reinforced with CRRT in which the TPCTs on the sunny shoulder are inclined at an angle based on the practical configuration of the embankment. Some corresponding conclusions and suggestions are proposed for a better design of CRRTs for the construction and possible reinforcement of railway embankments in permafrost regions.
The hydro-thermo-mechanical state is important for embankments in permafrost regions, especially for the embankments with shady and sunny slopes. It is difficult to determine the state because the complex hydro-thermo-mechanical interaction usually occurs within the embankments during freezing-thawing processes. To explore the thermo-mechanical stability of embankments in permafrost regions, an in-situ experiment of highway with asphalt pavement was performed firstly. Based on the observed results, a mathematical model was developed to describe the hydro-thermo-mechanical process. Subsequently, the model was validated by the observed data. Finally, the long-term stability of the embankment was analyzed and predicted with a climate warming rate of 0.052 °C/a. The results show that, (1) the asphalt pavement heat absorption effect and shady-sunny slope effect reduce the stability of the embankment; (2) the deformation of the embankment demonstrates the periodic freezing-thawing fluctuation and the long-term creep settlement characteristics; (3) the settlement is mainly caused by the freezing-thawing behavior of the active layer, the moving down of the permafrost table, and the warming of permafrost; (4) the shady-sunny slope effect induces the uneven settlement, and the settlement difference increases with operation time. The study will be helpful for the design and maintenance of embankments in permafrost regions.
Air and soil temperatures are important factors that contribute to hydro-thermal processes and ecosystem dynamics in permafrost regions. However, there is little research regarding soil thermal dynamics during freeze-thaw processes in permafrost regions with thermal orbits on the Tibetan Plateau. Thermal orbits can provide simplified illustrations of the relationships between air and ground temperatures. This paper presents a new quantitative analysis for thermal orbits by combining the characteristics of ellipse and linear regression theories. A sensibility analysis of thermal orbits was conducted with different air and ground temperatures and vegetation types on the Tibetan Plateau. Results indicated that the thermal orbit regression slopes and intercepts had variations in characteristics between air and ground temperatures at different depths. More specifically, both air and ground temperatures showed homologous variation with increasing depth. This type of analysis is important for a better understanding of permafrost thermal properties as they relate to soil moisture, climate change, and vegetation effects in permafrost regions on the Tibetan Plateau.
The Qinghai–Tibet Highway (QTH) in China has been experiencing a serious embankment settlement/heave for more than half a century. The settlement/heave is resulted from several mechanical processes taking place in different soil layers. In this paper, four typical settlement/heave patterns of road embankments in permafrost regions, namely “steady-low rate”, “fluctuate”, “down step” and “steady-high rate” are proposed based on 3-year monitored data of embankment settlement/heave and ground temperature at four road sections as well as previous published data of the QTH. Their formation mechanisms and evolution trend in the process of permafrost degradation are discussed from the viewpoints of engineering geology and mechanical process, based on the clarification of the deformation characteristics of different soil layers of a typical road embankment. The results show that the four patterns are caused by the negligible settlement/heave, freeze-thaw cycling in an open condition, consolidation of the thawed permafrost layers, and creep of warm permafrost layers respectively. The pattern will change from one to another during the process of permafrost degradation, which will become very complex with the occurrence of frost heave. The results can help revealing the deformation mechanism of road embankments in permafrost regions, and can benefit road construction and maintenance in the future.
This paper examines the applicability of a landslide susceptibility assessment approach to engineered slopes using data from the Irish Rail network. A logistical regression model was used to determine the susceptibility of landslide occurrence on an asset by asset basis using input factors derived specifically for man-made earthworks. Records of past failures were used to train the model to predict the probability of future failures occurring. The model was used to analyse a substantial section of the Irish Rail network comprising of 1184 slopes. The database of assets was split into training and validation datasets and similar levels of predictive performance were achieved with both datasets indicating the applicability and robustness of the approach. The results of the study show that simple asset databases, partially populated by visual survey data, can be used effectively to carry out a landslide susceptibility analysis. This enables proactive identification of critical assets as opposed to the current reactive industry standard, which represents an important step forward in creating objective risk rating systems for transport network earthworks.
Climate warming since the second half of the 20th century has begun to significantly impact infrastructure integrity in permafrost environments and has already resulted in expensive maintenance operations. Engineers in countries with permafrost are actively working to adapt the design of structures to degrading permafrost conditions. Here, we review permafrost degradation processes and their geotechnical impacts. We also summarise mitigation techniques for protecting transportation infrastructure built on permafrost and for preventing permafrost degradation near these facilities based on the results of field and laboratory tests, numerical simulations and engineering practices on such infrastructure. We draw four conclusions: (1) climate warming and local surface changes have caused permafrost degradation, and resulted in instability and damage leading to infrastructure maintenance and repair; (2) passive cooling methods, including high-albedo surfacing, sun-sheds, air convection embankments, air ducts, heat drains and thermosyphons, have shown consistent cooling effects, if designed appropriately; (3) mitigation and adaptation methods are more expensive than conventional construction techniques as shown by construction cost data for a test site in Canada; and (4) the influence of continued climate warming on permafrost and infrastructure design must be considered within the design of new or rehabilitated infrastructure and within the context of the infrastructure's service life. Copyright
The permafrost on the Qinghai-Tibet plateau(QTP) is degrading at present under the influence of Global Warming, which will greatly affect the stability of engineering structures and the ecosystem on the QTP. The variation of the air temperature and the process of permafrost degradation based on the air temperature in the permafrost regions on the QTP from 1955 to 2011 from four weather stations along the Qinghai-Tibet railway (QTR) were studied. The continuous ground temperatures over 35 years from two boreholes including a 15-meter-deep borehole on the sunny slope and a 35-meter-deep borehole on the shady slope of the mountain, acquired from the permafrost observational station at Fenghuoshan were analyzed. The annual mean air temperature in the permafrost regions along the QTR started to rise gradually in late 1950s, went down during 1970s, ascended back in the middle of 1980s and increased rapidly after 2000, and the rate of increasing is rising conspicuously. From 1978 to 2014, the annual mean ground temperature of the permafrost on the sunny slope of the Fenghuoshan climbed up by 0.91℃, and that on the shady slope also increased by 0.58℃ from 1964 to 2014. The permafrost is degrading because of the rising temperature. With the degradation of the permafrost, the type of geothermal temperature curves has transformed. The geothermal temperature curve of the sunny slope was changed from the initial positive geothermal gradient type to zero geothermal gradient type, then to the current minus geothermal gradient type. The geothermal temperature curve of the shady slope was changed from the initial positive geothermal gradient type to the zero geothermal gradient type. The degradation on the sunny slope is far more severe than that on the shady slope, which is mainly caused by the difference of ground temperature in cold seasons. The permafrost table is sensitive to the change of the annual mean air temperature and fluctuates with the climate change.
Landslide susceptibility mapping is one of the crucial stages of landslide hazard and risk assessment. Moreover, the susceptibility maps assist planners, local administrations, and decision makers in disaster planning. Various approaches have been applied in the literature to increase the accuracy of landslide susceptibility maps. The determination of suitable susceptibility mapping method plays critical role for obtaining required accuracy. In this study, the performances of three quantitative susceptibility mapping methods are evaluated. The logistic regression (LR) analysis is the typical example of statistical methods, while GIS-based multi-criteria decision analyses (MCDA) and association rule mining (ARM) are the examples of heuristic and data mining methods, respectively. The susceptibility maps based on the three methods are obtained for Şavşat in Artvin province (NE Turkey) where the region has intense landslides. The landslide influencing parameters for the study area are lithology, land use/land cover, soil type, erosion, altitude, slope, aspect, distance to drainage, soil depth, distance to fault, distance to road. The models for the three methods are then compared and evaluated by using pixel-based evaluation metrics. Results showed that ARM provides a higher quality percent (QP), whereas percent of damage detection (PDD) is higher for LR method. The lowest QP is obtained by GIS-based MCDA. It is found that LR and ARM methods are better than GIS-based MCDA in modeling the landslide susceptibility and they can be integrated to obtain better performance.
A centrifuge model test of sloping subgrade was conducted using the mechanical similarity when the freezing-thawing depth reaches the greatest. The deformation characteristics, influence factors as well as failure causes were researched. Compared with the in-situ test achievement of the natural slope in the permafrost region, the feasibility of the test scheme as well as the reliability of the results based on the mechanical similarity was verified. The results show that the root cause of the instability is the deficiency of shear resistance strength of the weak belt, resulting in the large deformation. Meanwhile, the deformation mainly concentrates on the shallow soil layer above the freezing-thawing interface, and the deformation mutation point takes place near the freezing-thawing interface. The crack slips along the freezing-thawing interface after cutting through the active layer. Under the experimental conditions, the reasonable height of embankment is 4.0-5.0 m.
Thermokarst lakes have been developing recently along the Qinghai-Tibet engineering corridor in association with increased human activity and persistent climatic warming. Based on field observations, we assessed the susceptibility of terrain to the development of thermokarst lakes between the Chumaerhe River and Fenghuoshan mountain pass. A susceptibility map of the region was created in a geographic information system by assessing seven controlling factors, ranked using the analytic hierarchy process. The resulting susceptibility values ranged between 0.1 and 0.66. These susceptibility values were divided into four classes (high, moderate, low, and lowest) according to the mutagenesis point method. Areas with values between 0.1 and 0.16 were considered to have the ‘lowest’ susceptibility, while those between 0.26 and 0.66 were considered to have ‘high’ susceptibility. Using SPOT-5 satellite data, we determined that the high-susceptibility areas contained approximately 91 % of the total thermokarst lake area in the study region, and 88 % of the number of lakes. The moderate, low, and lowest level areas accounted for about 52 % of the study region, but only contained 9 % of the total lake area and 12 % of the lakes. Finally, relations between the area of the thermokarst lakes and the main controlling factors, e.g., ground ice content, ground temperature, vegetation type, and altitude were discussed.
Crushed rock embankment (CRE) was most prevalent embankment structure with cooling measures along the Qinghai–Tibet Railway in permafrost regions. Ground temperature dataset from embankment construction (in 2002) to 2010 at nine monitoring sites along the railway were compiled to study long term cooling processes and cooling effects of CRE. Monitoring results indicated that the heat stored in filling materials could dissipate out in two cold seasons after embankment construction. Under cooling effect of CRE, permafrost tables beneath CRE moved upwards significantly during the first three years after embankment construction and then maintain almost constant. But underlying permafrost experienced different thermal process in relative warm and cold permafrost regions. In cold regions, underlying permafrost up to 14 m in depth experienced considerable cooling trends during the first five to sixth years after embankment construction. While in warm regions, the uppermost permafrost layer warmed after upwards movement of permafrost table, and underlying deep permafrost had no obvious cooling trends with time. Finally, differences in freezing and thawing seasons of, and differences in ground thermal regimes of cold and warm permafrost regions were investigated based on ground temperature from natural borehole. Then, the different cooling effects of CRE in two regions were interpreted based on these differences.
Thick permafrost was developed on the QTP during the early and middle Pleistocene with mean annual air temperatures (MAATs) 7 to 8 centigrade colder than today. During 1.1 to 0.6 MaBP, permafrost developed extensively when QTP rose to 3,500 m. The second maximum glaciation occurred during 0.8 to 0.6 MaBP, and permafrost was extensively developed. During the middle Pleistocene climatic warming, permafrost largely retreated. During 330 to 220 KaBP, permafrost was continuous. The Last Glaciation Maximum (LGM) occurred during 30 to 25 kaBP with MAATs 5 to 7 centigrade colder than today, mean annual ground temperatures (MAGTs) colder than -4 to -5 centigrade, and thicknesses of permafrost at 120 to 150 m. The lower limit of permafrost (LLP) extended down to 1,800 m. The post-LGM climate was warming, still with widespread permafrost, LLPs 1,000 m lower than today, and area of permafrost 70-80 per cent greater. During 10.8 to 8.5-7 kaBP, permafrost had retreated with LLPs on the margins up by 300-400 m. Although permafrost degraded, its total area still was 40-50 percent greater. During the Megathermal (8.5-7 to 4-3 kaBP), permafrost had largely retreated. In the interior, persistent downward thawing reached depths of 14 to 16 m. Permafrost survived in islands, or buried, or in mountains. Permafrost degradation in the east was more dramatic. The LLP was 300 to 400 m higher than today, MAATs 2 to 3 centigrade higher, and area of permafrost 40 to 50 percent of that at present. During 4-3 to 1 kaBP, the Neoglaciation resumed the cold climate. The LLP was about 300 m lower and MAATs were about 2 centigrade colder. Permafrost again expanded, and reached to the maximum in the end of the cold period. The area of permafrost was 20 to 30 per cent greater than today. In the interior, permafrost as thick as 30 m was developed. Due to the marginal nature, permafrost thawed to depths of 15 to 20 m during the Megathermal, but the newer permafrost formed during the later cold period was less than 15to 20 m in thicknesses. During 1,000 to 500 aBP, permafrost in marginal areas had largely disappeared, and downward degradation reached to depth of 10 m as a result of several small-scale warming. Two positions of relict permafrost table were identified. The first of late Holocene warming is at depth of 8.35 m, the second of the Megathermal is at depth of 16 m. The LLP, MAATs and permafrost area were 200 to 300 m and 1.5 to 2.0 centigrade higher, and 20 to 30 per cent less, respectively. During the Little Ice Age (500 to 100 aBP), permafrost started to develop again, with increasing areal extent and thickness. A new layer of permafrost of about 10 m was formed by downward freezing of soils, connecting with the second layer relict permafrost table of late Holocene warming. The LLP should be 150 to 200 m lower, the MAATs 0.8 to 1.5 centigrade colder, and area of permafrost 10 per cent greater. Climatic warming have been apparent during the past century, especially during the past 40 a. Seasonal thaw penetration has increased by 25 to 60 cm. The MAGTs have risen by 0.1 to 0.4 centigrade. Permafrost has been shrinking towards the interior, with a reduction of permafrost area of 6 to 8 percent, and the LLP has risen by 40 to 80 m. Permafrost degradation in the periphery island permafrost zones is the most striking. The vertical degradation of permafrost has resulted in taliks of tens of centimeters to 3 m in thicknesses. The MAATs are projected to rise by 2.2 to 2.6 centigrade during the next 50 years, permafrost degradation would be accelerating.
There is widespread ice-rich permafrost over Qinghai–Tibetan plateau. The exposure and subsequently thawing of ice-rich permafrost result in serious engineering and environmental consequences. However, it is often inevitable to expose ice-rich permafrost during the construction of railway, highway, or any engineering structures in permafrost regions. In this paper, we described the hazards induced from ice-rich permafrost exposure including slope instability, thermal slumping, soil erosion, frost heave and thaw settlement along Qinghai–Tibetan railway. The leading factors resulting in the occurrence of hazards were reviewed. Various remedial measures applied during the construction of Qinghai–Tibetan railway were introduced. The operation effects on avoiding failure or minimizing the damage consequence were discussed. The results show that ice-rich permafrost exposure generally causes cutting failure unless proper countermeasures are applied. Slope instability is the most serious damage for ice-rich permafrost cutting. Frost heaving and thaw settlement tend to damage the surface treatments and have lesser effects on railway operation. Experience shows that Coarse-grain soil replacement with insulation and drainage system are the most common measures to be applied. Cement concrete framework measure is more popular than turf covering and insulation covering due to its construction convenience and less cost. The results indicate that the treatment of turf covering is more suitable for ice-rich permafrost exposure than insulation covering due to high long-term performance rating and surface deformation adaptability. Retaining wall is an effective remedial measure to prevent slope failure of deep cut in permafrost regions. The field investigation shows that design and construction methods to deal with the exposure and thawing of ice-rich permafrost along Qinghai–Tibetan railway are efficient and these experiences are helpful for other projects in cold regions.
Based on field monitoring datasets, characteristics of embankment deformation were summarized along the Qinghai–Tibet Railway in four permafrost regions with different mean annual ground temperatures (MAGTs). Then, further analyses were carried out at some typical monitoring profiles to discuss mechanisms of these embankment deformations with consideration of detailed information of thermal and subsurface conditions. The results indicated that in regions with MAGT
The Qinghai-Tibet Railway (QTR) project was finished on July 1, 2006, and has served for over 3years. Judging from the present situation, the roadbed is stable and train speed in permafrost regions achieves 100km/h as expected during the designing. However, as half part of the roadbed was constructed over the permafrost characterized by high ground temperature and high ice content, slight changes of the permafrost might lead to roadbed problems, of which the settlement in embankment–bridge transition section is an obvious and special one. Investigated results of 164 bridges and accounting to 656 positions from the Xidatan Basin to the Chiqu Valley along the QTR in 2009 showed that the settlement was influenced by factors including bridge orientation, embankment slope direction, embankment height, ground temperature, ground ice content of permafrost and local subgrade soil type. For the average value of the settlement, it was greater at the northern end of a bridge than that at the southern end, and was greater in sunny-slope than that in shady-slope. It was greater in high ice permafrost regions than that in low ice regions, and was greater in high-temperature permafrost regions than that in low-temperature regions. Additionally, it increased logarithmically with the height of the embankment. In regions where the subgrade soils were dominated by silt, silty clay or fine sand, the settlement amount was higher than that in bedrock regions. Correlation analysis results showed that there were good relationships between the settlement and the slope direction, embankment height, ground temperature and ice contents when some of the later items were quantified. The correlation coefficients were 0.234, 0.213, −0.21 and 0.151 respectively, when the factors were quantified.
Current methods for estimating the long-term settlement of shallow foundations on frozen soils are reviewed. It is found that, when the distortional creep is the main source of settlement, there are some potentially good methods for its prediction. Much less is known, however, on how to predict the long-term settlement of shallow footings on relatively warm frozen soils, when both creep and consolidation act simultaneously. Other subjects considered in the paper are the selection of operational strength of frozen soils for the design, the ways of taking into account the effect of friction on their creep and strength, as well as the effects on the settlement of foundations of the depth of burial and the loading history. Finally, some areas of needed research are defined, with a special emphasis on the need for more long-term performance observations on full-scale footings in permafrost.
The assertion that pure conductive heat transfer always dominates in cold climates is at odds with decades of research in soil physics which clearly demonstrate that non-conductive heat transfer by water and water vapor are significant, and frequently are for specific periods the dominant modes of heat transfer near the ground surface. The thermal regime at the surface represents the effective boundary condition for deeper thermal regimes. Also, surface soils are going to respond more quickly to any climatic fluctuations; this is important to us because most facets of our lives are tied to earth's surface. To accurately determine the surface thermal regime (for example, the detection of climate change), it is important to consider all potential forms of heat transfer. Gradients that have the potential to alter the thermal regime besides temperature include pore water pressure, gravitational, density, vapor pressure and chemical. The importance of several non-conductive heat transport mechanisms near the ground surface is examined.
Many highway embankments experience problematic settlements. Compression of soil under the self-weight of the embankment generally occurs during construction, but postconstruction, wetting-induced collapse can result in more long-term settlement problems, depending on climate and movement of the wetting front. A study undertaken to examine settlement associated with unsatturated soil embarkments included centrifuge modeling of compacted silt embankments, laboratory testing of the embankment soil, and data interpretation with the focus on settlement prediction. A silty soil was selected to facilitate the measurement of matric suction using tensiometers. Three model embankments were constructed and tested in the Army Corps of Engineers Centrifuge Research Center in Vicksburg, Mississipi. Embankments 20 m high were simulated using centrifugal acceleration of 165 g. Embankments were constructed to achieve a relative compaction of 90 or 95 percent based on standard effort and moisture content between 2 and 5 percent dry of the optimum moisture content. Instrumentation used during self-weight compression and wetting included linear variable differential transformers and pore-pressure transducers equipped with high-air-entry porous stones. Results demonstrate the importance of the as-compacted water content and dry unit weight on the potential for wetting-induced collapse settlement. Settlement caused by self-weight compression and that caused by wetting-induced collapse are clearly discernable in results of centrifuge tests, allowing for comparison to settlement predictions. Results are discussed in light of typical compaction specification, oedometer-based predictions, and implications for the design of compacted embankments.
The former studies on embankment in permafrost regions indicate that the maximum thawed depth on the embankment central line is regarded as the evaluation criterion, through which the roadbed thermal stability is evaluated. In fact, thermal effect problems associated with slope orientations result in the maximum thawed depth position being deviated in the roadbed transverse direction rather than thawed on the embankment central line. So the thermal stability of the permafrost embankment will highly have been changed. In this paper, the thermal stability of permafrost embankment is modeled with the assumption that the air temperature will be warmed up by 0.022 °C/a when the running time is 20 a and 50 a, respectively. Different roadbed surfaces, different embankment heights and different roadbed strikes are all analyzed. Surface material includes gravelly and asphalt. Embankment height ranges from 0 m to 5.0 m with a step of 0.5 m. For the embankment strike, east to west (EW), southwest to northeast (SW–NE), south to north (SN) and symmetric route are taken into consideration. There are several significant findings summarized from the calculated results. Firstly, for the embankments with the shady–sunny slope that there are hardly linear relations between the changes of natural permafrost table and artificial permafrost table and the heights of embankment. Secondly, there are three results when the running time is 20 a: a) with the completely symmetric thermal boundary conditions and under both the gravelly and asphalt surfaces, there are almost linear relations between the changes of permafrost table and the embankment height; b) under the gravelly surface, for embankments with sunny–shady slopes, there is no linear relation between the changes of permafrost table and the embankment height; c) under the asphalt surface, for embankments with sunny–shady slopes, if the embankment is not high enough there is a linear relation between the changes of permafrost table and the embankment height, but the thermal stability cannot be reached. Thirdly, when the running time is 50 a, the thermal stability of all embankments cannot be reached other than the symmetric strike under the gravelly surface. Finally, when designing an embankment, besides considering the minimum embankment height and the maximum embankment height, the Yin-Yang Slope effect should be taken into account.
Results are presented for experimental laboratory investigations of mechanical suffosion, and a quantitative assessment of
the stress-strain state (SSS) is given for filtering masses of sandy soils.
The existing segregation potential (SP) method for frost heave prediction in soils is semiempirical in nature and does not explicitly predict the relationship between heave rate, temperature gradient, and other more fundamental soil properties. The SP method assumes that the heave rate is directly related to the temperature gradient at the frost front but acknowledges that the SP parameter is dependent on pressure, suction at the frost front, cooling rate, soil type, and so forth. This paper extends and modifies an approximate analytical technique of Gilpin and accounts for the effects of distributed phase change within the freezing fringe in both the head- and mass-transfer components of the formulation. The approach requires as input a relationship between frozen hydraulic conductivity and temperature and predicts the discrete location of each ice lens within the freezing soil. The solution can be carried out quickly on a microcomputer to obtain the heave, suction at the frost front, ice lens temperature, and other results of interest with time. Furthermore, the discrete ice lens method predicts the effects of changing overburden pressure on the predicted heave rate. A method of extracting input parameters for the discrete ice lens procedure from a series of frost heave tests is proposed. The discrete ice theory has been tested and calibrated against well-documented frost heave test results in the literature, and very encouraging agreement between prediction and observation has been obtained. Key words: frost heave, discrete ice lens, segregation potential, hydraulic conductivity of frozen soil, freezing soil.