Qinghai-Tibet Railway Research Articles

Monitoring surface deformation of permafrost in Wudaoliang Region, Qinghai–Tibet Plateau with ENVISAT ASAR data

Permafrost in Qinghai–Tibet Plateau (QTP) has been suffering from global warming in recent years, characterized by the deepening of the permafrost active layer. Seasonal changes in permafrost are usually reflected as ground surface deformation, which can be monitored by multi-temporal interferometric synthetic aperture radar (MT-InSAR) technology. Owing to the extreme environment in the QTP, there are few ground-based deformational observation data available, and records of permafrost monitoring by MT-InSAR with ground validation are limited. Here we present a study of surface deformation monitoring for permafrost with MT-InSAR technology validated by a large number of in-situ observations compared with the previous published results. In this study, a small baseline subset (SBAS) method was used with ENVISAT ASAR data in WuDaoLiang, QTP, to acquire the surface deformation and to analyze the corresponding characteristics. The results were first validated with 24 GNSS leveling observation points along the Qinghai–Tibet Railway, including numeric validation (e.g., statistics and KS test) between the InSAR derived deformation and the time-interpolated GNSS leveling values, and the variation trend of the two deformation sequences during a permafrost deformation period, at each observation point. Considering both the differences in magnitudes and trends, the deformation at 22 out of 24 points detected by InSAR corresponded well to the GNSS observation series over one year, which indicates the reliability of MT-InSAR for permafrost monitoring. After validation, the amplitudes and linear velocity of the InSAR deformation in this region were calculated and analyzed, together with selected points in different types of terrain. Generally, in the deformation map, most pixels show a trend of periodic and seasonal displacement, uplift in winter and subsidence in summer, with amplitudes of 3–10 mm in most regions. The deformation in mountain areas is less than that of flat lands in amplitude, and shows more randomness in periodic characteristics. Meanwhile, some points with obvious settlement have been detected, probably corresponding with permafrost degradation.

Multi-decadal geomorphic changes of a low-angle valley glacier in the East Kunlun Mountains: remote sensing observations and detachment hazard assessment

Abstract. Detachments of large parts of low-angle mountain glaciers in recent years have raised great attention due to their threats to lives and properties downstream. While current studies have mainly focused on post-event analysis, a few opportunities have presented themselves to assess the potential hazards of a glacier prone to detachment. Here we present a comprehensive analysis of the dynamics and runout hazard of a low-angle (∼20∘) valley glacier, close to the Qinghai–Tibet railway and highway, in the East Kunlun Mountains on the Qinghai–Tibet Plateau. The changes in morphology, terminus position, and surface elevation of the glacier between 1975 and 2021 were characterized with a stereo-image pair from the historical KH-9 spy satellite, six digital elevation models (DEMs), and 11 high-resolution images from Planet Labs. The surface flow velocities of the glacier tongue between 2009 and 2020 were also tracked based on cross-correlation of Planet images. Our observations show that the glacier snout has been progressively advancing in the past 4 decades, with a stepwise increase in advance velocity from 4.55±0.46ma-1 between 1975 and 2009 to 30.88±2.36ma-1 between 2015 and 2020. DEM differencing confirms the glacial advance, with surface thinning in the source region and thickening in the tongue. The net volume loss over the glacier tongue was about 11.21±2.66×105 m3 during 1975–2018. Image cross-correlation reveals that the surface flow velocity of the glacier tongue has been increasing in recent years, with the mean velocity below 4800 m more than tripling from 6.3±1.8ma-1 during 2009–2010 to 22.3±3.2ma-1 during 2019–2020. With a combined analysis of the geomorphic, climatic, and hydrologic conditions of the glacier, we suggest that the flow of the glacier tongue is mainly controlled by the glacier geometry, while the presence of an ice-dammed lake and a supraglacial pond implies a hydrological influence as well. Taking the whole glacier and glacier tongue as two endmember avalanche sources, we assessed the potential runout distances of these two scenarios using the angle of reach and the Voellmy–Salm avalanche model. The assessments show that the avalanche of the whole glacier would easily travel a distance that would threaten the safety of the railway. In contrast, the detachment of the glacier tongue would threaten the railway only with a small angle of reach or when employing a low-friction parameter in the Voellmy–Salm modeling.

Characteristics and prevention and control technology of blown sand environment with high altitude and cold temperature on Qinghai-Tibet Railway

<p indent=0mm>Since the beginning of the construction of the Golmud to Lhasa section of the Qinghai-Tibet Railway, sand damage has been a serious problem that cannot be ignored because it threatens the normal operation of the railway. Thus, alpine blown sand activity and its prevention and control must be studied urgently. Through continuous, systematic research on the blown sand environment and sand control engineering of the Golmud to Lhasa section of the Qinghai-Tibet Railway in recent years, we analyzed the characteristics of the blown sand hazards, proposed prevention and control concepts and a protection system configuration, and analyzed the protection benefits after the project was implemented. In this paper, the characteristics of a blown sand disaster and its prevention and control are summarized systematically, which fills the research gaps in terms of blown sand hazards in high altitude and cold regions, and provides a scientific basis and technical support for the prevention and control of blown sand hazards of railway projects in the Qinghai-Tibet Plateau and similar regions.

Numeričko ispitivanje seizmičkog ponašanja željezničkog nasipa u hladnim područjima

To investigate more fully seismic behaviour of the Qinghai-Tibet railway embankment, a comprehensive discussion and a781nalysis is conducted in this paper by applying a numerical technique. Specifically, the one dimensional equivalent linear ground response analysis was conducted in permafrost regions. On this basis, the seismic response of a typical railway embankment was further studied by applying the nonlinear dynamic finite element analysis method. As a result, nonlinear behaviour of permafrost sites was determined, and the dynamic acceleration, velocity and displacement of the embankment was discussed and the quantitative assessment was approximately estimated. The results indicate that the dynamic response of the embankment has distinct nonlinear characteristics. The peak ground acceleration coefficient at the embankment shoulder is larger than the natural ground surface, marking a 73% increase compared to the coefficient on the natural ground surface. When the seismic intensity reaches a certain value, a plastic zone gradually appears in the embankment, and a continuous extension of the plastic zone can be noted with an increase in peak acceleration of the input seismic wave. The findings of this research may provide an additional insight and have significant implications for further research of cold regions.

An integrated observation dataset of the hydrological and thermal deformation in permafrost slopes and engineering infrastructure in the Qinghai–Tibet Engineering Corridor

Abstract. Across the Qinghai–Tibet Plateau (QTP) there is a narrow engineering corridor with widely distributed slopes called the Qinghai–Tibet Engineering Corridor (QTEC), where a variety of important infrastructures are concentrated. These facilities are transportation routes for people, materials, energy, etc. from inland China to the Tibet Autonomous Region. From Golmud to Lhasa, the engineering corridor covers 632 km of permafrost containing the densely developed Qinghai–Tibet Railway and Qinghai–Tibet Highway, as well as power and communication towers. Slope failure in permafrost regions, caused by permafrost degradation, ground ice melting, etc., affects the engineering construction and permafrost environments in the QTEC. We implement a variety of sensors to monitor the hydrological and thermal deformation between permafrost slopes and permafrost engineering projects in the corridor. In addition to soil temperature and moisture sensors, the global navigation satellite system (GNSS), terrestrial laser scanning (TLS), and unmanned aerial vehicles (UAVs) were adopted to monitor the spatial distribution and changes in thermal deformation. An integrated dataset of hydrological and thermal deformation in permafrost engineering and slopes in the QTEC from the 1950s to 2020, including meteorological and ground observations, TLS point cloud data, and RGB and thermal infrared (TIR) images, can be of great value for estimating the hydrological and thermal impact and stability between engineering and slopes under the influence of climate change and engineering disturbance. The dataset and code were uploaded to the Zenodo repository and can be accessed through https://zenodo.org/communities/qtec (last access: 23 June 2021), including meteorological and ground observations at https://doi.org/10.5281/zenodo.5009871 (Luo et al., 2020d), TLS measurements at https://doi.org/10.5281/zenodo.5009558 (Luo et al., 2020a), UAV RGB and TIR images at https://doi.org/10.5281/zenodo.5016192 (Luo et al., 2020b), and R code for permafrost indices and visualisation at https://doi.org/10.5281/zenodo.5002981 (Luo et al., 2020c).

Cooling performance enhancement of a new expressway embankment in the Tibetan Plateau permafrost zone

The crushed-rock interlayer (CRI), as typical cooling technique used in the Qinghai-Tibet Railway, cannot be directly applied in expressways traversing permafrost areas because of the intense heat-absorption asphalt pavement. Sufficient cooling of permafrost foundation to meet the demand of engineering stability is an important issue. In this study, a CRI embankment combined with vertical ventilation ducts (VVDs) was designed to strengthen the convective cooling of wide expressways. To assess the performance of the combination design, a field experiment was conducted in the Tibet Plateau by building a full-scale expressway section. A numerical model was then developed and validated to analyze the heat transfer process and to predict its long-term thermal regimes considering climate warming. Results show that the new structure can produce an obviously increased convection cooling on permafrost foundation by enhancing the winter cold-energy utilization. The VVDs at the centerline play an effective role in dissipating heat accumulation in embankment center and can eliminate thermal asymmetry caused by plateau's prevalent wind direction. The combination of CRI and VVDs is effective to control ground temperature to improve expressway embankment stability. This new design could be considered for application in expressways built on permafrost stratum.

Research on Integrated Navigation Algorithm Based on Radial Basis Function Neural Network

The Qinghai-Tibet Railway is located on the Qinghai-Tibet Plateau in China. Due to its harsh climatic conditions and geographic environment, the line currently uses the Global Position System (GPS) to achieve train positioning. However, the navigation satellites are easily blocked by obstructions such as tunnels, resulting in a decrease in positioning accuracy. The conventional solution is to use multiple sensors such as an inertial navigation system (INS) for data fusion. But in the INS/GPS integrated navigation system, when the GPS signal is lost, the navigation accuracy will still decrease. In order to solve this problem, this paper proposes a radial basis function (RBF) neural network-assisted integrated navigation filtering algorithm. When the two systems are working normally, the measured raw information is used to train the RBF neural network. When the GPS fails, the measured and calculated values of the inertial navigation system are input to the trained network model to obtain the predicted error value, which is corrected to the inertial navigation system to obtain the final navigation information. The MATLAB simulation results show that when the short-term GPS information is missing, the integrated navigation system assisted by the RBF neural network has better estimation accuracy.

Hydrological ecosystem changes and impacts after the Zonag Lake outburst in Hoh Xil of Tibetan Plateau

After the iconic outburst of Zonag Lake in Hoh Xil of Tibetan Plateau (TP) in 2011, the causes of the collapse and its impact on the volume of water contained by the downstream lakes have highly been concerned, but the overall changes of the hydrological ecosystem and its impacts on the basin are yet not clear. This paper analyzes the hydrological system (lake area and hydrological connection) and ecosystem (sandstorm activity and vegetation growth status) changes and their impacts on the regional ecological environment after the outburst event, based on remotely sensed images from 2000 to 2020, meteorological observations, and field surveys. The results show that the outburst of Zonag Lake has not only changed the regional hydrology and ecosystem pattern but also caused a trend of degradation in the ecological environment of Zonag Lake Basin. Some lambing areas and active areas of Tibetan antelope in the area are being buried and eroded by the sandstorm. The downstream Yanhu Lake has risen to the highest level and overflowed through the emergency diversion engineering. These impacts are continuously threatening the health of the ecological environment of the world natural heritage site in Hoh Xil, the safety of Qinghai-Tibet highway, Qinghai-Tibet railway, and other engineering facilities, as well as the stability of fluvial geomorphology in the northern most sources of Yangtze River.

GIMMS NDVI3g+ (1982–2015) response to climate change and engineering activities along the Qinghai–Tibet Railway

Restricted by cold, drought and high altitude natural environments, vegetation ecological environment of the Qinghai–Tibet Plateau is fragile and difficult to repair when damaged. The purpose of this research is to reveal the characteristic of Normalized Difference Vegetation Index (NDVI) in direct impact area and ecological background area response to the engineering activities and global climate changes along Qinghai–Tibet railway. A framework was constructed by integrating a Gaussian fitting model, a buffer analysis, a trend analysis, a correlation analysis and a regression analysis method. The advantages of this framework are (1) Exploration of the impact of human and natural factors on the local vegetation ecological environment in pre-, co-, and post-construction of the railway; (2) Investigation of the time and extent of the impact of engineering activities on the plateau ecological environment; (3) Identify the contribution of climate change and engineering activities to changes of vegetation index. The framework was evaluated with GIMMS (Global Inventory Modeling and Mapping Studies) and MODIS (Moderate Resolution Imaging Spectroradiometer) NDVI from 1982 to 2001–2018. Results demonstrated that (1) Annual NDVI of the Qinghai–Tibet Railway was highly responsive to climate change and engineering activities, and shown a downward trend, upward trend for under construction and in operation period respectively. (2) Engineering activities of the Qinghai–Tibet Railway had a significant impact on vegetation along the route. Annual NDVI growth rate of ‘core area’ and ‘background buffer’ are quite different in pre-construction, under construction and in operation time. (3) Climate change along the Qinghai–Tibet Railway was significantly be responded to global changes during the 34 years. The air temperature and precipitation growth rate of the Golmud South–mountain Pass to Lhasa (GSPL) route is substantial lower than that of the Xining to Golmud South–mountain Pass (XGSP) route. Research results recommend that information on vegetation ecological environment is exploited by government agencies to ensure responsible ecological safety, traffic safety and sustainable development along the Qinghai–Tibet railway.

A Seamless Train Positioning System Using a Lidar-Aided Hybrid Integration Methodology

GNSS/INS integrated navigation and positioning technology is widely used for train operations applications seeking a decrease in dependence on trackside equipment. However, during train operations, environmental factors such as bridges, tunnels, hillsides, and buildings will block the satellite signals. When INS works in a stand-alone mode, the system errors accumulate with time due to the inertial sensor characteristics. To overcome this problem, light detection and ranging (lidar) equipment can be introduced to help control INS divergence. The lidar point cloud data is first processed using the random sample consensus (RANSAC) algorithm to determine the track plane, then the moving average filtering (MAF) algorithm is used to detect and classify the rails. The frogs can be detected based on the changing rail number and the constraint condition for turnout parameters. With the assistance of a previously surveyed turnout database, the geographical positions of the detected frogs can be obtained and integrated with INS data to converge INS sensor errors when GNSS is not available. In this paper a lidar-aided GNSS/INS integrated navigation system is proposed that can ensure continuous positioning in both GNSS-available and GNSS-blocked scenarios. GNSS/INS is applied when the system operates in the GNSS-available scenario, and switches to the INS/lidar mode when the GNSS signals are blocked. To evaluate the performance of the proposed system, an actual train experiment was conducted along the Qinghai-Tibet railway. The results confirm that the proposed lidar-aided navigation system can achieve accurate and continuous positioning. When GNSS is not available, the proposed method can effectively suppress the error of INS with a DRMS of 1.66 m, which is a 70.4% improvement compared with a conventional GNSS/INS integrated system.

Formation and evolution of suprapermafrost taliks beneath earth-filled embankments along the Qinghai-Tibet Railway in permafrost regions

Taliks are bodies or layers of unfrozen ground in permafrost areas. Suprapermafrost taliks (SPTs) formed between the active layer and permafrost table beneath embankments along the Qinghai-Tibet Railway (QTR) would reduce the stability of the embankments and thus threaten the safety of QTR operations, because the SPTs exhibit a lower bearing capacity than that of frozen ground. This study investigated the formation and evolution of SPTs beneath earth-filled embankments at two monitoring sites (P7 and P17) along the QTR in order to determine the SPTs formation mechanism. The SPTs under the left shoulder of the embankments at P7 and P17 were caused by thermal disturbance of filling and vertical heat accumulation, respectively. The mechanism of SPTs formation beneath the embankments was closely associated with the mean annual ground temperature and the height of embankment filling materials. The study findings can facilitate understanding the formation and evolution of SPTs beneath the embankments in similar sections along the QTR. In particular, the findings can serve as a guidance for the QTR administration bureau in implementing countermeasures for eliminating these unfrozen layers and increasing ground bearing capacity.

A new methodological framework coupling computational fluid dynamics and fingerprinting for assessment of aeolian sediment transport processes

A systematic understanding of the transport processes of aeolian sand from source to sedimentary areas is important for both hazard control and fundamental mechanism research. This study proposes a methodological framework consisting of wind data standardisation, computational fluid dynamics (CFD) simulation and fingerprinting technology to clarify aeolian sediment transport processes. The methodological framework was applied to the Cuona Lake section of the Qinghai-Tibetan Railway as a case study. One main finding was that the mountain passes located on the west of the lake act as outlets that converge and accelerate the predominant wind. The Basuoqu river valley and Amdo-Cuona down-faulted valley act as a ventilation tunnel in the sedimentary area. The CFD simulation clearly showed the influence of the complex terrain on the wind flow field. Second, the area southwest of the lake was predicted to be the main sediment source; a large portion of this area has an annual wind power density exceeding 1000 W/m2. Third, the fingerprinting estimation results revealed that the predicted main source area contributed more than 80% to the target sediment, which was in good agreement with the CFD simulation result. A decision-tree is provided to guide interested users in critical choices for different situations and research objectives. This CFD- and fingerprinting- based framework has the potential to contribute significantly to aeolian research and facilitate the development of a more detailed methodology.

Risk assessment of potential thaw settlement hazard in the permafrost regions of Qinghai-Tibet Plateau

Climate warming could exacerbate the occurrence of thaw settlement hazard in the permafrost regions of the Qinghai-Tibet Plateau (QTP), which would threaten the stability of engineering infrastructure in cold regions. The risk associated with permafrost settlement, valuable for the regional sustainable development, remains poorly assessed or understood on the QTP. In this study, three common Geo-hazard indices were used to assess the settlement risks in the permafrost regions of the QTP, including the settlement index, the risk zonation index, and the allowable bearing capacity index. However, large spatial differences existed in simulating the risk maps by using the abovementioned Geo-hazard indices. Hence, we developed a combined index (Ic) by integrating the three indices to reduce the uncertainty of the simulations. The results indicated that the ground ice is a critical factor for assessing the settlement risk in permafrost regions. We also applied the Ic to assess the settlement risk along the Qinghai-Tibet Railway (QTR). The proportion of low-risk area along the QTR would be the highest (45.38%) for the future periods 2061–2080 under Representative Concentration Pathway 4.5. The medium-risk area combined with the high-risk area would be accounted for more than 40%, which were located at the boundary of the present permafrost regions. Therefore, the corresponding adaptation measures should be taken to reduce the potential economic losses caused by the high-risk regions to the infrastructure. Overall, the results would present valuable references for engineering design, construction and maintenance, and provide insights for early warning and prevention of permafrost thaw settlement hazard on the QTP.

Evaluation of damage probability of railway embankments in permafrost regions in Qinghai–Tibet Plateau

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. • Statistically analysis of ten years’ worth of monitoring and reinforcement data of QTR embankments. • Distribution of deformed QTR embankments and embankment damage rate in permafrost regions. • Causes of embankment deformation, case records of reinforcement and maintenance measures. • Model to evaluate the damage probability of QTR embankments in permafrost regions.

Strengthening effect of crushed rock revetment and thermosyphons in a traditional embankment in permafrost regions under warming climate

The embankment of the Qinghai–Tibet Railway (QTR) has been experiencing severe problems due to permafrost degradation, especially in warm and ice-rich permafrost regions. Based on ground temperature and deformation data of the embankment at location K1497 + 150 of the QTR in 2006–2018, the thermal regime and deformation process were analysed. The results showed that 1) the degradation rate of permafrost under the embankment was faster than that under the natural site without engineering construction, and 2) the deformation rate of the embankment had exceeded the safety range for the QTR embankment before adopting mitigative measures. In addition, this study evaluated the cooling effect on the underlying permafrost and working mechanism of two strengthening measures. Two measures, crushed rock revetment (CRR) and thermosyphons, were adopted to protect the underlying permafrost from continual degradation. The individual cooling effect of the CRR was not as good as that of the thermosyphons. However, the combination of the two could enhance the protective effects of each on the underlying permafrost, effectively cooling the permafrost and improving the stability of the embankment.

Feasibility analysis of semi-welded seamless turnout in Yuqomolangma Station of Qinghai-Tibet Railway

It is difficult to lay seamless turnouts on the Qinghai-Tibet Railway, and the large temperature difference between day and night on the plateau railway leads to large changes in the temperature of the turnouts. Aiming at the equipment status of No.1 turnout in the Yuzhufeng station of the Qinghai-Tibet railway, a non-linear finite element calculation model of P60-12 single-open turnout was established. The long rail was calculated and analyzed based on the construction lock rail temperature and the local maximum and minimum rail temperature. The development law of displacement under temperature changes, after comparing the field measured displacement observation data, the model calculation result is correct, and the lateral displacement meets the requirements. Comparing and analyzing on-site rail displacement observation data, the model calculation results meet the engineering accuracy requirements. In the season of the highest rail temperature in the year, strain sensors are installed at the rail waist at different parts of the semi-welded seamless turnout to collect the rail strain increment under the cyclic change of rail temperature. According to the strain increment change rule, displacement observation data and model calculation results, it is concluded that the scheme of laying a semi-welded seamless turnout in Yuqomangma station is feasible, and the rail in the bifurcation area is stable under the action of temperature stress.

Prediction of temperature field of embankment in permafrost region of Qinghai Tibet railway

Temperature field distribution of Qinghai-Tibet railway is important for analyzing embankment stability. Based on the finite element method, the analysis model of temperature field is developed for predicting the changes in embankment thermal field in the following 40 years. The results show that the permafrost will degenerate to seasonally frozen soil.

Overview of the Measures and Techniques Used to Protect Traffic Lines against Shifting Sands in China

Shifting sands are one of the main contributors to desertification in China. This paper briefly reviews the measures and techniques which are used to protect traffic lines by stabilizing and fixing sands in the desert and desertification-affected arid and semi-arid areas in north China. We introduce the types and features of these measures and techniques, including mechanical, chemical, and biological measures, and outline how they have been applied in different areas and in different traffic lines over the past six decades, from 1950s to 2010s, taking the Baotou-Lanzhou railway, the Qinghai-Tibet railway, and the Tarim Desert highway as examples Mechanical measures such as erecting sand-retaining wind walls and placing straw checkerboards have proved to be very efficient for stabilizing shifting sands and protecting traffic lines that pass through the desert areas. Chemical measures are not widely used in the current sand fixing systems because of their high cost and potential pollution risks. Biological measures are preferred because they exhibit much better sand fixation performance and longer duration than the former two types of measures despite their relatively high cost. A combination of different measures is usually adopted in some areas to attain better sand-fixing effects. Stabilizing sand dune surfaces with mechanical measures or irrigation from underground water or river if available helps early recruitment of some drought-tolerant plants (xerophytes). We also point out the restrictions for existing sand-fixing measures and techniques and future research orientation. This review has implications for addressing eco-environmental issues associated with infrastructure construction that is part of the Belt and Road Initiative in desert and desertification-affected arid and semi-arid areas in the Mongolian Plateau.

Deformation behaviour and influence mechanism of thaw consolidation of embankments on the Qinghai-Tibet Railway in permafrost regions

With the thermal disturbance caused by engineering construction and global warming, thaw consolidation has become a primary source of subgrade deformation in permafrost regions. Based on the large-strain consolidation theory described by the updated Lagrangian, we study the thermal stability and the thaw consolidation in an ordinary subgrade at the warm and ice-rich permafrost (WIRP) site of the Beiluhe Qinghai-Tibet Railway (QTR) by establishing a thermo-mechanical coupled model. The research results are as follows: The initial mean annual ground temperature (MAGT) of the site influences the permafrost degradation on the Qinghai-Tibet Plateau due to construction and climate warming, exacerbating the thaw consolidation and creep of the ice-rich permafrost. The settlement rate and subgrade settlement increase with increasing embankment height, ice-rich permafrost layer thickness, and initial MAGT. Railway maintenance methods, such as ballast filling and track lifting, increase the subgrade weight, thus increasing the WIRP subgrade settlement. Furthermore, we predict the thaw consolidation of the DK1136 section of the QTR for the next 50 years. The prediction formulas of the cumulative settlements of the subgrade top and permafrost are established, and various suggestions for maintaining the railway subgrade of the WIRP site are proposed.

Extraction and analysis of saline soil deformation in the Qarhan Salt Lake region (in Qinghai, China) by the sentinel SBAS-InSAR technique

The instability of saline soil foundation affects the safety of artificial construction, and may cause ground collapse, building destruction and road damage. It is fundamental to reduce the potential engineering geological disasters by exploring the dynamic evolution of saline soil. Most of the previous researches of saline soil were conducted by simulated experiments and traditional geodetic surveying methods. Restricted to the limited sampling points, the spatiotemporal evolution characteristics of saline soil were difficult to find out in a large scale. This paper exploited SBAS-InSAR method to extract the deformation of the Qarhan Salt Lake (in Qinghai, China) section along Qinghai-Tibet railway, based on 119 image data acquired by Sentinel-1A from 2015 to 2020. The results showed that the deformation trends varied frequently in this saline mud flat. Between the adjacent areas with different deformation trends along Qinghai-Tibet railway, discontinuities caused by uplift and subsidence were very obvious. Besides, among the areas with brine exploitation or artificial construction, the maximum subsidence rate reached50 mm/yr, and the maximum cumulative subsidence exceeded 320 mm in the latest 5 years. In the saline mud flat closed to the rivers and lakes, the deformation trend was continuous uplift. Nevertheless, there were obvious seasonal deformation characteristics in those areas far away from the water body. Further analysis found out a sharply subsidence caused by the salt collapsibility appeared in rainy seasons. While an uplift trend induced by the salt swelling or frost heave was remarkable in dry seasons. Subsequently, the relationships were analyzed between the time series deformation and external environmental factors. Furthermore, the deformation mechanism of saline soilin the Qarhan Salt Lake region was interpreted then. In general, this study provides complete spatiotemporal evolution information of saline soil, and demonstrates the deformation characteristics of saline soil in the Qarhan Salt Lake region successfully. Related results would contribute to the safety monitoring for large-scale infrastructure construction in the saline soil areas.