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Assessment of Diseases in Embankment–Bridge Transition Section With Methodological Detection Along the Qinghai‐Tibet Railway in Permafrost Regions
Abstract
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.
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Electrical resistivity tomography (ERT) is a minimally invasive geophysical method that produces a model of subsurface resistivity from a large number of electrical resistance measurements. Strong resistivity contrasts usually exist between frozen and unfrozen earth materials, making ERT an effective and increasingly utilized tool in permafrost research. In this paper, we review more than 300 scientific publications dating from 2000 to 2022 to identify the capabilities and limitations of ERT for permafrost applications. The annual publication rate has increased by a factor of 10 over this period, but several unique challenges remain, and best practices for acquiring, processing, and interpreting ERT data in permafrost environments have not been clearly established. In this paper, we make recommendations for ERT surveys of permafrost and highlight recent advances in the field, with the objective of maximizing the utility of existing and future surveys.
Retrogressive thaw slumps (RTSs), which frequently occur in permafrost regions of the Qinghai-Tibet Plateau (QTP), China, can cause significant damage to the local surface, resulting in material losses and posing a threat to infrastructure and ecosystems in the region. However, quantitative assessment of ground ice ablation and hydrological ecosystem response was limited due to a lack of understanding of the complex hydro-thermal process during RTS development. In this study, we developed a three-dimensional hydro-thermal coupled numerical model of a RTS in the permafrost terrain at the Beilu River Basin of the QTP, including ice–water phase transitions, heat exchange, mass transport, and the parameterized exchange of heat between the active layer and air. Based on the calibrated hydro-thermal model and combined with the electrical resistivity tomography survey and sample analysis results, a method for estimating the melting of ground ice was proposed. Simulation results indicate that the model effectively reflects the factual hydro-thermal regime of the RTS and can evaluate the ground ice ablation and total suspended sediment variation, represented by turbidity. Between 2011 and 2021, the maximum simulated ground ice ablation was in 2016 within the slump region, amounting to a total of 492 m ³ , and it induced the reciprocal evolution, especially in the headwall of the RTS. High ponding depression water turbidity values of 28 and 49 occurred in the thawing season in 2021. The simulated ground ice ablation and turbidity events were highly correlated with climatic warming and wetting. The results offer a valuable approach to assessing the effects of RTS on infrastructure and the environment, especially in the context of a changing climate.
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.
Ground-penetrating radar (GPR) is an established technology with a wide range of applications for civil engineering, geological research, archaeological studies, and hydrological practices. In this regard, this study applies bibliometric and scientometric assessment to provide a systematic review of the literature on GPR-related research. This study reports the publication trends, sources of publications and subject categories, cooperation of countries, productivity of authors, citations of publications, and clusters of keywords in GPR-related research. The Science Citation Index Expanded (SCI-EXPANDED) and the Social Sciences Citation Index (SSCI), which can be accessed through the Web of Science Core Collection, are used as references. The findings report that the number of publications is 6880 between 2001 and 2021. The number of annual publications has increased significantly, from 139 in 2001 to 576 in 2021. The studies are published in 894 journals, and the annual number of active journals increased from 68 in 2001 to 215 in 2021. Throughout the study, the number of subject categories involved in GPR-related research fluctuated, ranging from 38 in 2001 to 68 in 2021. The research studies originated from 118 countries on 6 continents, where the United States and the People’s Republic of China led the research articles. The top five most common keywords are ground-penetrating radar, non-destructive testing, geophysics, electrical resistivity tomography, and radar. After investigating the clusters of keywords, it is determined that civil engineering, geological research, archaeological studies, and hydrological practices are the four main research fields incorporating GPR utilization. This study offers academics and practitioners an in-depth review of the latest research in GPR research as well as a multidisciplinary reference for future studies.
Human engineering activities and climate warming induce permafrost degradation in the Da Xing’anling Mountains, which may affect the distribution of permafrost and the safety of infrastructure. This study uses the electrical resistivity tomography method, in combination with field surveys and ground temperature monitoring, to investigate the distribution and degradation characteristics of permafrost and influencing factors at a typical monitoring site (MDS304) near the China-Russia Crude Oil Pipeline (CRCOP). The results show that the isolated permafrost in this area is vulnerable to further degradation because of warm oil pipelines and thermal erosion of rivers and ponds. The isolated permafrost is degrading in three directions at the MDS304 site. Specifically, the boundary between permafrost and talik is on both sides of the CRCOP, and permafrost is distributed as islands along a cross-section with a length of about 58–60 m. At present, the vertical hydrothermal influence range of the CRCOP increased to about 10–12 m. The active layer thickness has increased at a rate of 2.0 m/a from about 2.4–6.8 m to 2.5–10.8 m from 2019 to 2021 along this cross-section. Permafrost degradation on the side of the CRCOP’s second line is more visible due to the river’s lateral thermal erosion, where the talik boundary has moved eastward about 12 m during 2018–2022 at a rate of 3.0 m/a. It is 2.25 times the westward moving speed of the talik boundary on one side of the CRCOP’s first line. In contrast, the talik boundary between the CRCOP’s first line and the G111 highway also moves westward by about 4 m in 2019–2022. Moreover, the maximum displacement of the CRCOP’s second line caused by the thawing of frozen soil has reached up to 1.78 m. The degradation of permafrost may threaten the long-term stability of the pipeline. Moreover, the research results can provide a useful reference for decision-makers to reduce the risk of pipeline freeze-thaw hazards.
Active layer thickness (ALT) is a sensitive indicator of response to climate change. ALT has important influence on various aspects of the regional environment such as hydrological processes and vegetation. In this study, 57 ground-penetrating radar (GPR) sections were surveyed along the Qinghai–Tibet Engineering Corridor (QTEC) during 2018–2021, covering a total length of 58.5 km. The suitability of GPR-derived ALT was evaluated using in situ measurements and reference datasets, for which the bias and root mean square error were approximately −0.16 and 0.43 m, respectively. The GPR results show that the QTEC ALT was in the range of 1.25–6.70 m (mean: 2.49 ± 0.57 m). Observed ALT demonstrated pronounced spatial variability at both regional and fine scales. We developed a statistical estimation model that explicitly considers the soil thermal regime (i.e., ground thawing index, TIg), soil properties, and vegetation. This model was found suitable for simulating ALT over the QTEC, and it could explain 52% (R2 = 0.52) of ALT variability. The statistical model shows that a difference of 10 °C.d in TIg is equivalent to a change of 0.67 m in ALT, and an increase of 0.1 in the normalized difference vegetation index (NDVI) is equivalent to a decrease of 0.23 m in ALT. The fine-scale (<1 km) variation in ALT could account for 77.6% of the regional-scale (approximately 550 km) variation. These results provide a timely ALT benchmark along the QTEC, which can inform the construction and maintenance of engineering facilities along the QTEC.
Permafrost in the NE European Russian Arctic is suffering from some of the highest degradation rates in the world. The rising mean annual air temperature causes warming permafrost, the increase in the active layer thickness (ALT), and the reduction of the permafrost extent. These phenomena represent a serious risk for infrastructures and human activities. ALT characterization is important to estimate the degree of permafrost degradation. We used a multidisciplinary approach to investigate the ALT distribution in the Khanovey railway station area (close to Vorkuta, Arctic Russia), where thaw subsidence leads to railroad vertical deformations up to 2.5 cm/year. Geocryological surveys, including vegetation analysis and underground temperature measurements, together with the faster and less invasive electrical resistivity tomography (ERT) geophysical method, were used to investigate the frozen/unfrozen ground settings between the railroad and the Vorkuta River. Borehole stratigraphy and landscape microzonation indicated a massive prevalence of clay and silty clay sediments at shallow depths in this area. The complex refractive index method (CRIM) was used to integrate and quantitatively validate the results. The data analysis showed landscape heterogeneity and maximum ALT and permafrost thickness values of about 7 and 50 m, respectively. The active layer was characterized by resistivity values ranging from about 30 to 100 Ωm, whereas the underlying permafrost resistivity exceeded 200 Ωm, up to a maximum of about 10 kΩm. In the active layer, there was a coexistence of frozen and unfrozen unconsolidated sediments, where the ice content estimated using the CRIM ranged from about 0.3 – 0.4 to 0.9. Moreover, the transition zone between the active layer base and the permafrost table, whose resistivity values ranged from 100 to 200 Ωm for this kind of sediments, showed ice contents ranging from 0.9 to 1.0. Taliks were present in some depressions of the study area, characterized by minimum resistivity values lower than 10 Ωm. This thermokarst activity was more active close to the railroad because of the absence of insulating vegetation. This study contributes to better understanding of the spatial variability of cryological conditions, and the result is helpful in addressing engineering solutions for the stability of the railway.
The present study presents three‐dimensional investigations of a hydrostatic pingo in the Mackenzie Delta region and a hydraulic pingo in the Ogilvie Mountains and contributes to a better understanding about the internal structures of the two pingo types. A combined approach using quasi‐three‐dimensional electrical resistivity tomography, ground‐penetrating radar and frost probing allowed a clear delineation of frozen and unfrozen areas in the subsurface. At the hydrostatic pingo a massive ice core as well as a surrounding talik could be detected, but the location of the ice core and the talik differs from previous published assumptions. In contrast to acknowledged theory, at our site the massive ice core is not located in the center of the pingo but at the western edge, whereas the eastern flank is underlain by a talik, which surrounds the massive ice core. At the hydraulic pingo, the expected internal structure could be confirmed and the pathway of upwelling water could also be detected. The combined approach of the applied methods represents the first known three‐dimensional geoelectrical investigation of pingos and provides new insights into the internal structure and architecture of the two different pingo types. The chosen approach allows further conclusions on the formation of these permafrost‐affected landforms.
The riverine sediment flux (SF) is an essential pathway for nutrients and pollutants delivery and considered as an important indicator of land degradation and environment changes. With growing interest in environmental changes over the Tibetan Plateau (TP), this work investigated the variation of the SF in response to climate change in the headwater of the Yangtze River over the past 30 years. Annual time series of hydro-meteorological variables during 1986–2014 indicate significantly increasing trends of air temperature, precipitation, ground temperature, river discharge, suspended sediment concentration and SF. Stepwise changes were identified with significantly higher values of the above variables in 1998–2014 compared with 1986–1997, which could potentially be attributed to the strong 1997 El Niño event. Double-mass plots indicated that both meltwater and rainfall contributed to the increased river discharge while the increased SF mostly resulted from enhanced erosive power and transport capacities of the increased discharge. However, it was buffered by a decrease in sediment source due to the shift of maximum monthly rainfall from June/July to July/August during which period a denser vegetation cover prevents soil erosion. Partial least squares structural equation modeling analysis confirmed the dominance of warming on the increase of discharge amplified by increased precipitation. It also confirmed that the increased precipitation drives the increase in suspended sediment concentration. Both processes conspire and equally contribute to the stepwise increase of SF. This study provides important insights into the controlling processes for recent SF changes and gives guidance for water and soil conservation on the TP.
Hydrogeologic processes and shallow subsurface flows control runoff generation, groundwater dynamics, and permafrost distribution at high latitudes and elevations. Electrical resistivity tomography (ERT) can effectively delineate the frozen and thawed zones in the cold environment and can be applied in permafrost hydrogeology by measuring the differences in subsurface electrical potential. A combined approach of ERT and borehole measurements is implemented to map the flow paths of the supra-permafrost and sub-permafrost waters around the Wanlong Worma Lake (WWL) basin in the headwaters of the Yellow River (northeastern Qinghai-Tibet Plateau, China). The ERT sounding results are further validated using drilling records and measured data on ground temperatures and groundwater level. Then, basic features for permafrost hydrogeology are outlined according to the ERT sounding, vegetation distribution, and geological data in the WWL basin. The results show the presence of permafrost at depths up to 15 m, in which electrical resistivity is >250 Ωm. Below the permafrost (at depth 15–80 m), electrical resistivity is generally <100 Ωm. At the depth where an aquifer occurs (20–60 m), electrical resistivity is in the range 1–25 Ωm. The sub-permafrost water moves towards the zone of taliks (unfrozen ground) under the hydraulic gradient controlled by local permafrost distribution and is affected by terrain relief. This work demonstrates the capability of ERT for delineating the distribution of the aquifers of the supra- and sub-permafrost waters and for understanding changes in hydraulic connections in a rapidly degrading alpine permafrost basin.
Air temperature increases thermally degrade permafrost, which has widespread impacts on engineering design, resource development, and environmental protection in cold regions. This study evaluates the potential thermal degradation of permafrost over the Qinghai–Tibet Plateau (QTP) from the 1960s to the 2000s using estimated decadal mean annual air temperatures (MAATs) by integrating remote-sensing-based estimates of mean annual land surface temperatures (MASTs), leaf area index (LAI) and fractional snow cover values, and decadal mean MAAT date from 152 weather stations with a geographically weighted regression (GWR). The results reflect a continuous rise of approximately 0.04 ∘C a-1 in the decadal mean MAAT values over the past half century. A thermal-condition classification matrix is used to convert modelled MAATs to permafrost thermal type. Results show that the climate warming has led to a thermal degradation of permafrost in the past half century. The total area of thermally degraded permafrost is approximately 153.76×104 km2, which corresponds to 88 % of the permafrost area in the 1960s. The thermal condition of 75.2 % of the very cold permafrost, 89.6 % of the cold permafrost, 90.3 % of the cool permafrost, 92.3 % of the warm permafrost, and 32.8 % of the very warm permafrost has been degraded to lower levels of thermal condition. Approximately 49.4 % of the very warm permafrost and 96 % of the likely thawing permafrost has degraded to seasonally frozen ground. The mean elevations of the very cold, cold, cool, warm, very warm, and likely thawing permafrost areas increased by 88, 97, 155, 185, 161, and 250 m, respectively. The degradation mainly occurred from the 1960s to the 1970s and from the 1990s to the 2000s. This degradation may lead to increased risks to infrastructure, reductions in ecosystem resilience, increased flood risks, and positive climate feedback effects. It therefore affects the well-being of millions of people and sustainable development at the Third Pole.
Permafrost is determined to a large extent by the Earth’s surface temperature, therefore it distributes mainly in high altitude and latitude regions. However, stable, warm (about −1 °C) permafrost occurs within a scree slope in northern China that is more than 600 km south of the southernmost limit of latitudinal permafrost on the Eurasian Continent. It is at an elevation of only 900 m above sea level (ASL). The area has a mean annual air temperature (MAAT) of 6 to 8 °C. Thermal processes of the scree slope, investigated through field monitoring and numerical simulation, showed that the permafrost is caused by winter air convection within the porous rock deposits and is stable as air convection does not occur in summer time. The deposit is covered by a 30-cm-thick peaty soil layer dated (carbon C-14) to between 1,000 to 1,600 years ago. The layer also contributes to the permafrost’s existence due to the peat’s thermal conductivity offset when frozen and thawed. The existence of permafrost under such warm climatic conditions confirms the effectiveness of using crushed rock layer as basement or slope cover to protect the warm permafrost subgrade of the recently-constructed Qinghai-Tibet Railway (QTR), even under the predicted climate warming conditions.
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.
Railway track transition zone is a zone where track stiffness changes abruptly. This change occurs where the slab track connects
to a conventional ballasted track, at the abutments of open-deck bridges, at the beginnings and ends of tunnels, at road and
railway level crossings, and at locations where rigid culverts are placed close to the bottom of sleepers. In this paper,
ballasted and slab tracks are simulated by two-dimensional model with two-layer masses. The transition zone is divided into
three segments, each having a length of 6 meters with different specification and stiffness. The model of track consists of
a Timoshenko beam as a rail and slab, lumped mass as sleepers, and spring and damper as ballast, sub-grade, and rail pad.
The results of the dynamic analysis are presented and compared in two circumstances — one considering the transition zone
and the other its absence.
The method of numerical analysis of the differential scanning calorimetry (DSC) thermogram obtained during warming makes it possible to obtain a complete curve of the unfrozen water content in frozen soil, including the highest temperature at which last ice crystals melt and the unfrozen water content becomes equal to the total water content. This is referred to as the freezing point of the soil–water system obtained on melting. Statistical analysis of 137 results obtained for 6 monomineral and homoionic model soils implies that, similarly to the freezing point obtained from the cooling curves, the soil freezing point obtained on melting strongly depends on the water content. An empirical equation, found basing on the reported results, has proved to be useful as a predicting tool with reference to 33 foreign data points obtained in the typical way (i.e., from the cooling curve).
A small-diameter nuclear magnetic resonance (NMR) logging tool has been developed and field tested at various sites in the United States and Australia. A novel design approach has produced relatively inexpensive, small-diameter probes that can be run in open or PVC-cased boreholes as small as 2 inches in diameter. The complete system, including surface electronics and various downhole probes, has been successfully tested in small-diameter monitoring wells in a range of hydrogeological settings. A variant of the probe that can be deployed by a direct-push machine has also been developed and tested in the field. The new NMR logging tool provides reliable, direct, and high-resolution information that is of importance for groundwater studies. Specifically, the technology provides direct measurement of total water content (total porosity in the saturated zone or moisture content in the unsaturated zone), and estimates of relative pore-size distribution (bound vs. mobile water content) and hydraulic conductivity. The NMR measurements show good agreement with ancillary data from lithologic logs, geophysical logs, and hydrogeologic measurements, and provide valuable information for groundwater investigations.
Under global warming scenarios, the passive method of simply increasing the thermal resistance by raising the embankment height
and using insulating materials has been proven ineffective in warm and ice-rich permafrost areas and therefore could not be
used in the Qinghai-Tibet Railway engineering. Instead, a proactive “cooled-roadbed” approach was developed and used to lower
the ground temperature in order to maintain a perennially frozen subgrade. The concept that local and site-specific factors
play an important role in the occurrence and disappearance of permafrost has helped us to devise a number of measures to cool
down the roadbed. For example, we adjust and control heat transfer by using different embankment configurations and fill materials.
The Qinghai-Tibet Railway project demonstrates that a series of proactive roadbed-cooling methods can be used to lower the
temperature of permafrost beneath the embankment and to stabilize the roadbed. These methods include solar radiation control
using shading boards, heat convection control using ventilation ducts, thermosyphons, air-cooled embankments, and heat conduction
control using “thermal semi-conductor” materials, as well as combinations of above mentioned three control measures. This
roadbed-cooling approach provides not only a solution for engineering construction in sensitive permafrost areas but also
a countermeasure against possible global warming.
The Qinghai–Tibet Highway and Railway (the Corridor) across the Qinghai–Tibet Plateau traverses 670 km of permafrost and seasonally frozen-ground in the interior of the Plateau, which is sensitive to climatic and anthropogenic environmental changes. The frozen-ground conditions for engineering geology along the Corridor is complicated by the variability in the near-surface lithology, and the mosaic presence of warm permafrost and talik in a periglacial environment. Differential settlement is the major frost-effect problem encountered over permafrost areas. The traditional classification of frozen ground based on the areal distribution of permafrost is too generalized for engineering purposes and a more refined classification is necessary for engineering design and construction. A proposed classification of 51 zones, sub-zones, and sections of frozen ground has been widely adopted for the design and construction of foundations in the portion of the Corridor studied. The mean annual ground temperature (MAGT), near-surface soil types and moisture content, and active faults and topography are most commonly the primary controlling factors in this classification. However, other factors, such as local microreliefs, drainage conditions, and snow and vegetation covers also exert important influences on the features of frozen ground. About 60% of the total length of the Corridor studied possesses reasonably good frozen-ground conditions, which do not need special mitigative measures for frost hazards. However, other sections, such as warm and ice-rich or -saturated permafrost, particularly in the sections in wetlands, ground improvement measures such as elevated land bridges and passive or proactive cooling techniques need to be applied to ensure the long-term stability of thermally unstable, thick permafrost subsoils, and/or refill with non-frost-susceptible soils. Due to the long-history of the construction and management of the Corridor by various government departments, adverse impacts of construction and operation on the permafrost environment have been resulted. It is recommended that an integrated, executable plan for the routing of major construction projects within this transportation corridor be established and long-term monitoring networks installed for evaluating and mitigating the impact from anthropogenic and climatic changes in frozen-ground conditions.
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.
Two-phase closed thermosyphons (TPCTs) are widely used in enhancing mechanical strength of foundation soils in permafrost regions. However, engineering problems develop in embankments containing TPCTs. Based on numerical simulations, we herein discuss the influence of four important parameters, namely model size, daily variations in air and ground surface temperatures (AGST), decreasing cooling power of a TPCT, and adiabatic section, on the simulation accuracy or the application results of a TPCT. Results show that the simulated thermal influence of the TPCT can be severely impacted by the model size. It is also found that neglecting daily AGST variations results in 0.3–0.4 °C temperature increase in soil 2 m away from the TPCT. The decreasing cooling power of a TPCT can increase the ground temperature. When the cooling power decreases by 30% and 50%, the ground temperature 2 m away from the TPCT increases by 0.2–0.3 °C and 0.4–0.6 °C in cold seasons, respectively. Although adiabatic section was applied in many TPCTs, but it has limited effect on the cooling performance of a TPCT. The results may help improving the accuracy of a simulation model and help optimize field applications of TPCTs in cold regions.
The warming and thawing of ice-rich permafrost pose considerable threat to the integrity of polar and high-altitude infrastructure, in turn jeopardizing sustainable development. In this Review, we explore the extent and costs of observed and predicted infrastructure damage associated with permafrost degradation, and the methods available to mitigate such adverse consequences. Permafrost change imposes various threats to infrastructure, namely through warming, active layer thickening and thaw-related hazards such as thermokarst and mass wasting. These impacts, often linked to anthropogenic warming, are exacerbated through increased human activity. Observed infrastructure damage is substantial, with up to 80% of buildings in some Russian cities and ~30% of some road surfaces in the Qinghai–Tibet Plateau reporting damage. Under anthropogenic warming, infrastructure damage is projected to continue, with 30–50% of critical circumpolar infrastructure thought to be at high risk by 2050. Accordingly, permafrost degradation-related infrastructure costs could rise to tens of billions of US dollars by the second half of the century. Several mitigation techniques exist to alleviate these impacts, including convection embankments, thermosyphons and piling foundations, with proven success at preserving and cooling permafrost and stabilizing infrastructure. To be effective, however, better understanding is needed on the regions at high risk.
The embankment–bridge transition section (EBTS) is one of the zones where railway diseases occur frequently in permafrost regions. Disease risk assessment of EBTSs can provide guidance for maintenance. In this study, considering the engineering geological conditions, climate characteristics, and embankment structure types along the Qinghai–Tibet Railway (QTR) as well as based on the disease inventory of the QTR from 2010 to 2019, the logistic regression (LR), support vector machine (SVM), and combination-weight-based gay relation analysis (GRA) were used for disease risk assessment of the EBTSs along the QTR in permafrost regions. The results indicate that the LR and SVM models have a better capability for EBTS disease prediction than the GRA model, and the SVM model can select more disease samples in relatively larger regions than the LR model. Based on the SVM and LR models, the risk level of EBTSs is divided into four classes: low- (29.9%), moderate- (39.6%), high- (22.1%), and very high (8.4%) risk. Finally, we selected 272 EBTSs in high- and very-high-risk classes for key observation during the maintenance of the QTR in permafrost regions. This study provides a reference for the risk assessment of railways built in permafrost regions using data-driven methods.
The embankment construction in permafrost regions changes the energy balance on the surface, resulting in the degradation of the underlying permafrost and instability in the embankment structure. Considering the strict evenness requirement for an expressway, large deformation and instability in expressway embankment cannot be allowed. Accordingly, in this study, a composite measure combined with two-phase closed thermosyphons (TPCTs) and insulation boards is proposed for stabilizing embankments. Moreover, a full-scale experimental expressway embankment is constructed in the Qinghai–Tibet Plateau (QTP) to analyze and investigate the stability of the composite embankment. The experimental results show that the composite measure significantly cools the permafrost under the embankment center and shady slope, and reliably alleviates the embankment deformation and deformation difference. However, the special ground temperature distribution around the TPCTs causes the asymmetric thermal regime and longitudinal cracks in the composite embankment. Additional reinforcement measures should be developed to alleviate the asymmetric thermal regime and prevent such longitudinal cracks. Moreover, timely repair of existing cracks and taking waterproofing measures in advance are favorable for embankment stability.
Icing occurs each winter along the floodplain of the Kuuguluk River in the continuous permafrost zone at Salluit in Nunavik (Quebec), Canada. The source of successive water overflows which thicken and enlarge this ice cover over time is suprapermafrost groundwater discharging from a talik below the riverbed. Electrical resistivity tomography was used to delineate the talik, while water level and temperature dataloggers were used to assess the thermo‐hydraulic conditions of the riverbed. The mean annual riverbed temperature was 1.8°C in 2016 while the mean annual air temperature was −6.0°C. Hydraulic heads below the ice cover as high as 2.8 m and events of abrupt decreases in hydraulic head due to suprapermafrost groundwater overflow through cracks in the ice cover were monitored. An analytical solution based on beam mechanics theory was used to assess the water pressure‐induced stresses which are sufficient to fracture the ice cover. A detailed conceptual model of the talik and icing dynamics is proposed to explain the cryo‐hydrogeological processes taking place in this complex groundwater–river system. The groundwater pressure buildup in the talik during the winter is due to constricted flow of suprapermafrost groundwater in the talik. These results have implications for understanding the dynamics of river taliks and their use as potential water supplies in northern communities.
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.
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.
Track transitions such as bridge approaches, road crossings and shifts from slab track to ballasted track are common locations where track degradation accelerates due to dynamic and high impact forces; as a consequence there is higher differential settlement. These types of discontinuities cause an abrupt change in the structural response of the track due mainly to variations in stiffness and track damping. Track transition zones are prone to an accelerated deterioration of track material and geometry that leads to increased maintenance costs. Track deterioration also leads to vehicle degradation due to enhanced acceleration, low frequency oscillation, and high frequency vibrations. While ballast deterioration is a major factor affecting the stability and longevity of rail tracks, the cost of tackling transition related problems that detract from passenger comfort is also high. A good transition zone lessens the impact of dynamic load of moving trains by minimising the abrupt variations in track stiffness and ensuring a smooth and gradual change from a less stiff (ballasted track) to a stiff (slab track) structure. This paper presents a critical review of various problems associated with transition zones and the measures adopted to mitigate them; it also includes critical review of research work carried out using large-scale laboratory testing, mathematical and computational modelling and field measurements on track transition zones.
Landslides in the Thompson River valley, British Columbia, Canada, have historically impacted vital transportation infrastructure, the environment and natural resources, cultural heritage features, communities, public safety, and the economy. To better understand and manage geohazard risks in Canada’s primary national railway corridor, government agencies, universities, and railway industry partners are focusing research efforts on Ripley Landslide, 7 km south of Ashcroft. Electrical resistivity tomography (ERT) datasets collected in November 2013 (on land) and November 2014 (over water) were successfully combined and inverted into a pseudo-3D model that produced significantly deeper resistivity values than previously available in 2D profiles. The lithology, degree of saturation, porosity, presence of dissolved electrolytes, and temperature all influence electrical resistivity of earth materials in the landslide. Continuous (real-time) ERT monitoring began in November 2017 to characterize the long-term hydrological behavior of geological units in the landslide. Seventy-two electrodes were positioned in two arrays across the slide body and connected to a proactive infrastructure monitoring and evaluation (PRIME) system with internet access. PRIME resistivity results corroborate data from other geophysical techniques and hints at an unusual distribution pattern for surface moisture and groundwater in fractured bedrock and overlying clay-rich sediments containing vertical tension cracks and discrete sub-horizontal planar features interpreted as slide surfaces within pre-sheared zones. A greater understanding of the composition and internal structure of slope failures in the valley is gained at the site from terrain analysis and modeling of multi-dimensional geophysical datasets. This insight helps with the interpretation of multi-year monitoring datasets and will guide future efforts to record landslide activity in the valley, reducing stakeholder risks.
In order to explore more economic filling alternatives than typically used graded gravel + 5% cement in a high-speed railway transition zone, engineering properties of graded gravel (without cement) and A, B group filling (well graded coarse-grained soil with less than 30% of fine-grained soil) were tested. This is followed by the establishment of a 3D vertical coupling dynamic model of a tunnel-culvert-tunnel transition section based on the D'Alembert’s principle of energy weak variation and the Lagrange scheme. The model results have been validated against the in situ measurements. The analysis from the model show that both graded gravel and A, B group filling are well-graded with high strengths, and the dynamic responses of the roadbed supported by the two fillings are both less than allowable values at the speed of 350 km/h. However, the curves of vertical displacement along the longitudinal transition section are great like a shape of “W” with the A, B group filling in the transition zone. Therefore, the graded gravel is recommended to be more suitable than the A, B group filling for the studied tunnel-culvert-tunnel transition zone. This recommendation may be applicable to the case with a rock subgrade underneath to support the transition zone. Comparatively, for a soil subgrade under the transition zone, our results indicate that graded gravel + 5% cement is still the best filling material, while the other two less stiffer filling materials would result in considerable fluctuations to the roadbed surface.
Long-term thermal effects of air convection embankments (ACEs) over 550-km-long permafrost zones along the Qinghai-Tibet railway were analyzed on the basis of 14-year records (2002-2016) of ground temperature. The results showed that, after embankment construction, permafrost tables beneath the ACEs moved upward quickly in the first 3 years and then remained stable over the next 10 years. The magnitude of this upward movement showed a positive correlation with embankment thickness. Shallow permafrost temperature beneath the ACEs decreased over a 5-year period after embankment construction in cold permafrost zones, but increased sharply concurrent with permafrost table upward movement in warm permafrost zones. Deep permafrost beneath all the ACEs showed a slow warming trend due to climate warming. Overall, the thermal effects of ACEs significantly uplifted underlying permafrost tables after embankment construction and then maintained them well in a warming climate. The different thermal effects of ACEs in cold and warm permafrost zones related to the working principle of the ACEs and natural ground thermal regime in the two zones.
In a permafrost environment, supra-permafrost water is an important local factor affecting the shallow ground thermal regime and also plays a significant role in geotechnical problems. In this study, the impacts of supra-permafrost water ponding and drainage on the thermal regime and settlement characteristics of a railway embankment in continuous permafrost zone, the interior of the Qinghai-Tibet Plateau were investigated using 13-year records (2003–2016) of field measured data. Results showed that, because of the great latent heat of the ponded water alongside the embankment, a zero curtain layer (ZCL) as much as 5.5 m thick developed in and beneath the embankment after embankment construction in 2003. A three-layered thermal regime developed in the embankment and the subgrade. Although crushed rock revetments were installed 5 years after embankment construction, no soil cooling occurred beneath the ZCL and the ZCL remained stable in thickness. Meanwhile, embankment settlement developed quickly and nearly linearly from 2003 to 2012, with a cumulative settlement approaching approximately 160 mm at both the sunny and the shady embankment shoulders. Compression and creep of warm and ice-rich permafrost layer (WIPL) beneath the ZCL are considered as the main contributors to this significant settlement. Following drainage of the ponded water during 2012, the ZCL cooled quickly and completely frozen after two cold seasons. The underlying permafrost table moved upwards into the embankment and the WIPL cooled with time. Embankment settlement also slowed significantly. However, an asymmetrical temperature field developed in the embankment and the subgrade because of the sunny-shady embankment slope effect, leading to differential settlement between the sunny and the shady embankment shoulders.
To analyse the damage characteristics of thermosyphon embankments in a permafrost region, the Qingshui River section along the Qinghai-Tibet Highway (QTH) was used as a case study in which a field investigation and drilling were performed. The field soils were sampled, and their water content, dry density and compaction degree were tested in the laboratory. Based on the measured temperature data of the thermosyphon embankment, damage characteristics and possible associated causes were analysed. The major damage found in thermosyphon embankments was a longitudinal crack, which developed 1.0 to 2.0 m away from the thermosyphon. In partial sections, waves and other damage also occurred. The damage was primarily attributed to the non-uniform temperature distribution, which resulted in a non-uniform distribution of the mechanical properties of the embankment filling. Under a heavy traffic load, stress concentration phenomena occurred at the freezing-thawing interface that gradually developed into a longitudinal crack with increased highway operation. The embankment damage history, rainfall seepage, ponding near the embankment and freezing-thawing cycles further accelerated the development of damage along the thermosyphon embankments. According to the characteristics and causes of thermosyphon embankment damage, precisely computing the cooling efficiency of thermosyphon in the design stage is necessary to prevent freezing-thawing interface waves resulting from excessive cooling effectiveness, to reduce thermal erosion from ponding near the embankment by improving embankment drainage systems, and to set necessary structural measures at thermosyphon embankments that can improve their strength.
Soil thermodynamic properties are critical for determining the soil freezing and thawing depths of active layers which is highly important for the hydrology and energy balances of permafrost regions. Here, three soil thermal conductivity parameterizations were evaluated against detailed field measurements at two field sites in the permafrost region of Qinghai-Xizang (Tibet) Plateau (QXP). The results revealed that the comprehensive parameterization based on different schemes for calculating soil thermal conductivity is relatively close to the measured values in unfrozen soil, and Johansen's parameterization is the best in the frozen soil. Then, we first combined three thermal conductivity parameterizations with a freeze-thaw algorithm to simulate freezing and thawing depths of multi-layered soil. The analysis showed that the average percentage difference between the observed and calculated soil thawing depth values for the Johansen's and comprehensive parameterization was 10.42% and 8.49% at Tanggula (TGL) and Xidatan (XDT), receptively. It indicated that the comprehensive parameterization with freeze-thaw algorithm simulated the soil thawing depth more similarly to the observed data for multi-layered soil. These findings can also be incorporated into other land surface, hydrological or ecosystem models to simulate the freeze-thaw cycles in permafrost regions.
Both the inflow and outflow of supra-permafrost water to lakes play important roles in the hydrologic process of thermokarst lakes. The accompanying thermal effects on the adjacent permafrost are required for assessing their influences on the development of thermokarst lakes. For these purposes, the lake water level, temperature dynamics and supra-permafrost water flow of a lake were monitored on the Qinghai-Tibet Plateau (QTP). In addition, the spatial and temporal variation of the active layer thickness and permafrost distribution around the lake were investigated by combining ground penetrating radar (GPR), electrical resistivity tomography (ERT) and borehole temperature monitoring. The results revealed that the yearly unfrozen supra-permafrost water flow around the lake lasted approximately five months. The temperature and water level measurements during this period indicate that the lake water was recharged by relatively colder supra-permafrost water from the north-western lakeshore and was discharged through the eastern lakeshore. This process, accompanied by heat exchange with the underlying permafrost, might cause a directional difference of the active layer thickness and permafrost characteristics around the lake. Specifically, the active layer thickness variation was minimal and the ice-rich permafrost was found adjacent to the lakeshore along the recharge groundwater pathways, whereas a deeper active layer and ice-poor permafrost were observed close to the lakeshore from which the warm lake water was discharged. This study suggests that the lateral flow of warm lake water can be a major driver for the rapid expansion of thermokarst lakes and provides clues for evaluating the relationships between the thermokarst expansion process and climate warming.
The development of thermokarst lakes in permafrost regions can relate to climate change and significantly impact the hydrological regime. We investigated the configuration of permafrost and a talik under a thermokarst lake on the Qinghai–Tibet Plateau (QTP), China, using GPR, electrical resistivity tomography, drilling and ground temperature measurements. The boundaries and ice content of permafrost and the talik were identified adjacent to and under the lake. The thickness of permafrost differed by about 4 m on opposite sides of the lake. The thickness and extent of ice-rich permafrost under the northwest shore was greater than under the southeast shore. A talik penetrated the permafrost base beneath both the shallower and deeper parts of the lake, where water depths were all less than the maximum thickness of winter ice. The talik was wider beneath shallower parts of the lake than in deeper areas. This investigation demonstrates that a through-talik developed although the water depth was less than the maximum thickness of winter ice, indicating that the general relation between water depth and ice thickness is not reliable for identifying the nature of taliks on the QTP. Copyright © 2017 John Wiley & Sons, Ltd.
Fire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire-induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. We present a combination of multi-scale remote sensing, geophysical, and field observations that reveal details of both near-surface (<1 m) and deeper impacts of fire on permafrost. Along 11 transects that span burned-unburned boundaries in different landscape settings within interior Alaska, subsurface imaging indicates locations where permafrost appears to be resilient to disturbance from fire, areas where warm permafrost conditions exist that may be most vulnerable to future change, and also where permafrost has thawed. High-resolution geophysical data corroborate remote sensing interpretations of near-surface permafrost, and also add new high-fidelity details of spatial heterogeneity that extend from the shallow subsurface to depths of about 10 m. Data collected along each transect include observations of active layer thickness (ALT), organic layer thickness (OLT), plant species cover, electrical resistivity tomography (ERT), and downhole Nuclear Magnetic Resonance (NMR) measurements. Results show that post-fire impacts on permafrost can be variable, and depend on multiple factors such as fire severity, soil texture, and soil moisture.
The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation may be very large within a short distance. One example is when an unsupported sleeper is hanging in the rail. Track stiffness is then, locally at that sleeper, very low. At insulated joints the bending stiffness of the rail has a discontinuity implying a discontinuity also of the track stiffness. A third example of an abrupt change of track stiffness is the transition from an embankment to a bridge. At switches both mass and stiffness change rapidly. The variations of track stiffness will induce variations in the wheel/rail contact force. This will intensify track degradation such as increased wear, fatigue, track settlement due to permanent deformation of the ballast and the substructure, and so on. As soon as the track geometry starts to deteriorate, the variations of the wheel/rail interaction forces will increase, and the track deterioration rate increases. In the work reported here the possibility to smooth out track stiffness variations is discussed. It is demonstrated that by modifying the stiffness variations along the track, for example by use of grouting or under-sleeper pads, the variations of the wheel/rail contact force may be considerably reduced.
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.
The thermal convection of fluid inside ballast layer and ripped-rock layer, which are regarded as porous media in railway embankment, is the process of heat and mass transfer. In this paper, in order to research the influence of different embankment structures and geometries on the underlying permafrost thermal regime along Qinghai-Tibetan Railway, a numerical representation of the unsteady two-dimensional continuity, momentum (non-Darcy) and energy equations of thermal convection for incompressible fluid in porous media is used to analyze temperature characteristics of a traditional ballast embankment, a horizontal ripped-rock embankment and two U-shaped ripped-rock embankments for the 50 years. The calculated results indicate: (1) the traditional ballast embankment will cause the great degradation of the underlying permafrost under the assumption that the air temperature will warm up 2.6 °C in the 50 years; (2) the U-shaped ripped-rock embankment with 150-cm-thick ripped-rock layer and 160-cm-wide ripped-rock revetment can efficiently protect the underlying permafrost. However, 120-cm-thick horizontal ripped-rock layer has weak cooling effect. Therefore, the horizontal ripped-rock layer thickness is a very important factor to the effect of ripped-rock embankment. These analyses indicate that reasonable ripped-rock embankment structure and embankment geometry can provide an effective mechanism for preserving permafrost under trend of global warming and avoiding large deformation and embankment failure due to thaw settlement in high-temperature permafrost regions along Qinghai-Tibetan Railway.
Over one half of the permafrost along the Qinghai–Tibet Railway is “warm” and approximately 40% ice-rich. Under global warming, the construction of the Qinghai–Tibet Railway needs to consider climate changes over the next 50–100 years. Recent estimates indicate that the air temperature on the plateau will increase by 2.2–2.6 °C by 2050. Thus, the key to the success of the railway construction lies in preventing the permafrost underlying roadbeds from thawing. It has been more than 100 years since the first railway was built over permafrost. A frost damage ratio of greater than 30% has been reported for all the railroads built in permafrost regions. Based upon the experience and lessons learned from roadway constructions over permafrost, this paper proposes a more proactive design approach for the construction of the Qinghai–Tibet Railway. This approach focuses on cooling down the roadbed by lowering the ground temperature and is different from the passive method of preventing permafrost from thawing by simply increasing thermal resistance (e.g., increasing embankment height and using insulating materials). This “roadbed cooling” design approach is especially relevant to “warm” and ice-rich permafrost areas. A number of measures can be taken to cool down the roadbed, including proper selection of roadbed material and configurations to adjust solar radiation, heat convection, and heat conduction patterns in and/or around the roadbed.
A New Structure of Roadbed‐Abutment Transition Part on Permafrost
- Liu J.