Thaw Settlement Research Articles

Thermal state of soils in the active layer and underlain permafrost at the kilometer post 304 site along the China-Russia Crude Oil Pipeline

On-site monitoring is very important for understanding formation mechanisms of frost hazards frequently occurring in pipeline foundation soils and for designing and deploying according mitigative measures in permafrost regions. Significant thaw subsidence of ground surfaces along the China-Russia Crude Oil Pipeline (CRCOP) from Mo'he to Daqing, Heilongjiang Province, Northeast China have been observed at some segments underlain by ice-rich, warm (>1.0°C) permafrost since the official operation in January 2011. Recent monitoring results of the thermal states of foundation soils at the kilometer post (KP) 304 site along the CRCOP are presented in this paper. The results indicate that during the period from 2012 to 2014, shallow soils (at the depths from 0.8 to 4.0 m from ground surface) has warmed by approximately 1.0°C in the lateral range of 1.2 to 2.1 m away from the pipeline axis, and deeper permafrost (such as at the depth of 15 m, or the depth of zero annual amplitude of ground temperatures) by 0.08°C per year 4 m away from the pipe axis, and 0.07°C per year 5 m away from the pipeline axis. The results indicate an all-season talik has developed around and along the CRCOP. The thaw bulb, with a faster lateral expansion (compared with the vertical growth), enlarges in summer and shrinks in winter. This research will provide important references and bases for evaluating thermal influences of warm pipeline on permafrost and for design, construction, operation and maintenance of pipelines in permafrost regions.

Interannual variations in the hydrothermal regime around a thermokarst lake in Beiluhe, Qinghai-Tibet Plateau

Thermokarst is a term associated with the thaw of ice-rich permafrost and the resulting formation of irregular depressions in the landscape from thaw settlement. Thermokarst lakes may subsequently develop from ponds formed in depressions. These lakes commonly have collapsing shorelines, and the development of thermokarst terrain and associated thermal erosion may significantly influence the stability of infrastructure and the hydrothermal conditions of the surrounding permafrost. In this study, we examined interannual variations in the hydrothermal regime of a thermokarst lake in Beiluhe Basin based on field data measured in 2006–2013. The timing and nature of lake ice growth and melt were recorded. We observed considerable seasonal differences in lake water level (~0.5m) and differences in water level between the lake and the water table in the surrounding ground (over 1.0m). The nearly-saturated ground at the lakeshore (~35% in maximum volumetric water content) highlights the seepage effect from the lake to the surrounding ground. The vertical temperature profile from +2m (air) to −2m (lake bottom) and to 60m depth in the ground was measured. The annual mean air temperature, lake-surface temperature, and annual mean lake-bottom temperature in 2010–2011 were approximately −3.6, 0.4, and >5°C, respectively. The thermal offsets between the air and the lake surface and between the lake surface and lake bottom were 3 and 7°C, respectively. The annual mean lake-bottom temperatures ranged from 2.3 to 6.9°C at water depths from 1.2 to 2.1m. The asymmetry of the bathymetry has resulted in distinct thermal regimes beneath the lake bottom in different locations. A through-talik was present at the deepest side of the lake, but some permafrost extended laterally beneath the lake bottom at the shallower side, forming an hourglass shape in cross section at one end. Lateral thermal erosion along the lakeshore was linked to the lake-bottom temperature and lake depth. Variation in permafrost table depth from the lake center to the lakeshore was greater on the east side near deeper water (≥2m) than at the west side where water was shallower (≤70cm). The results from this study have highlighted the hydrothermal relations between thermokarst lake development and permafrost conditions.

Thaw Subsidence in Undisturbed Tundra Landscapes, Barrow, Alaska, 1962–2015

AbstractIn some regions underlain by ice‐rich permafrost, a consistent, long‐term increase in ALT under changing climatic conditions is not supported by observations. The apparent lack of ALT may be attributed to soil consolidation from thawing of the uppermost ice‐rich permafrost and subsidence of the ground surface. Four plots established in 1962 at Barrow, Alaska, were re‐instrumented in 2003 and surveyed annually using differential GPS technology, accompanied by active‐layer probing. Elevation change from 1962 to 2003 was within the interannual variability of the 2003–15 period, indicating net stability in the area. Over the 2003–15 period, however, all four plots experienced subsidence trends of 0.4–1.0 cm/year, resulting in a net elevation change of 8–15 cm. Warmer winters and increased snow depth during this period decreased the potential for frost heave. Warmer summers resulted in thaw penetration into the ice‐rich transient layer and ice wedges, leading to the net subsidence in recent years. Copyright © 2016 John Wiley & Sons, Ltd.

Modeling the performance of an air convection embankment (ACE) with thermal berm over ice-rich permafrost, Lost Chicken Creek, Alaska

Construction of roadway embankments over permafrost often results in settlement due to thawing of ice-rich foundation soils. The air convection embankment (ACE) is a relatively new design developed to reduce thaw settlement. In 2012 an ACE and an adjacent thermal berm were constructed as part of a realignment of the Taylor Highway near Lost Chicken Creek, Alaska. The Taylor Highway, a minor roadway with a gravel surface, is closed and not maintained during the winter months. To evaluate the thermal performance of the newly-constructed ACE and thermal berm, we performed field work and laboratory testing to determine foundation soil and embankment properties, measured temperatures at the base of the embankment, and developed two-dimensional finite element models to estimate long-term stability. Measurements indicated temperatures beneath the ACE were significantly colder than beneath the thermal berm. In the modeling, we simulated plowed (PC) and snow-covered (SC) conditions. Both models indicated that the ACE experienced density-driven air convection during the winter months. The PC scenario produced significantly colder temperatures within the ACE and underlying foundation soils. The SC model results more closely matched measured temperatures beneath the ACE, which is reasonable considering the lack of maintenance on the Taylor Highway during winter. The modeling indicates that ACE performance is improved through plowing of the surface, and that an ACE is more effective in maintaining frozen conditions in the foundation soils than the thermal berm; in fact, the modeling and measured temperatures indicate that the thermal berm actually raises the temperature in the foundation soils. Based on the results, we expect that thaw settlement will occur beneath the thermal berm until thermal equilibrium is reached, whereas the majority of the ACE will remain stable.

Experimental study on the anti-jacking-up performance of a screw pile for photovoltaic stents in a seasonal frozen region

The soils in seasonal frozen regions freeze and thaw frequently, causing severe frost heave and thaw settlement problems, which bring challenges to piles of photovoltaic stents. In this paper, laboratory tests are conducted with different types of screw piles under freezing conditions, with also using smooth piles for contrast. The aim is to simulate the freezing process of screw piles according to practical working conditions based on the similarity principle. Internal thermal resistance is ignored. The change laws of temperature, displacement, as well as the influence factors of types of screw piles are analyzed. The results indicate that: with a freezing depth of 30 cm, which is half of the pile length, large-double-bladed screw piles perform the best in antijacking-up, while all-bladed screw piles perform the worst, independent of the types of soil samples tested. The fitting relationship between jacking-up displacement and freezing depth is also proposed for each type of pile. Results obtained can provide an important reference to site construction in seasonal frozen regions.

Combined freeze-sealing and New Tubular Roof construction methods for seaside urban tunnel in soft ground

Construction of seaside urban tunnels is significantly difficult due to the densely adjacent buildings and underground facilities in conjunction with unfavourable geological conditions. For this, this paper investigates the construction methods used for Gongbei Tunnel, which is a typical seaside tunnel connecting Hong Kong-Zhuhai-Macau Bridge in China. The construction methods and stability of the undercutting section will be focused. In the tunnel section of interest, dozens of thick steel tubes are jacked into the soft soil, and freeze-sealing method is applied to form a thick water-proofing wall. In this study, the combined freezing and New Tubular Roof (NTR) method are simulated by thermo-mechanical coupling analysis. The temperature field obtained in the freezing process indicates that the thickness of frozen wall grows approx. 2.0m after 50days of freezing. Besides, the stability of the surrounding ground and supporting structures in the bench-cutting stage are also investigated. Then the thawing process is simulated and associated suggestions for post-grouting to prevent excessive thawing settlement are proposed. The numerical results show that the tunnel is stable and the influence of tunnel excavation on adjacent buildings is within the permissible range. It also shows that the designed construction methods can be used to adequately meet safety and stability standards when adopting the proposed construction and supporting system.

Investigation of the freeze–thaw states of foundation soils in permafrost areas along the China–Russia Crude Oil Pipeline (CRCOP) route using ground-penetrating radar (GPR)

The China–Russia Crude Oil Pipeline (CRCOP) was built to transport Siberian crude oil across 1030km of frozen ground. The Chinese portion of the CRCOP crosses 441km of discontinuous permafrost zones along the eastern flanks of the Da Xing'anling (Hinggan) Mountains. Significant thaw settlement of some of the pipeline foundation soils has occurred since the pipeline began operating in January 2011. The differential thaw settlement around the pipeline at the transitions between the thaw-settling and thaw-stable zones may lead to displacement or even buckling of the pipeline. To evaluate the engineering safety and long-term stability of pipeline foundations, ground-penetrating radar (GPR) was used to detect the freeze–thaw states of pipeline foundation soils in the permafrost zones. From April 2012 to November 2013, a total of 2780m of GPR profiles and 62 cross-sections (perpendicular to the CRCOP route) were obtained at eight GPR study sites on various terrains and vegetative coverage, with different thermal insulation configurations around the pipe, and with and without thermosyphons installed. The GPR profiles were interpreted and cross-checked with data from drilling, hand-dug pit or trench excavations, and ground temperature measurements. The results showed that the foundation soils around the pipeline were thawing, with maximum thaw depths under the pipeline of about 1.1m to 4.5m from the pipe bottom and increased maximum thaw depths of 0.5m to 3.7m during the period of this study. However, GPR profiles from the areas with dense vegetative coverage, and with pipe insulation of 80-mm-thick extruded polystyrene (XPS), and also with vertical thermosyphons installed, showed that permafrost foundation soils were thermally better protected, with only minor thaw settlement. The thermal states of pipeline foundation soils and the underlying permafrost varied markedly with different terrains. The drainage patterns and engineering activities, especially the heating from operating oil flows at an average annual oil temperature of 7.7°C (with a range of 0.7°C to 20.4°C) along the pipeline route may have been responsible for the extensive and substantial thaw subsidence in the ice-rich permafrost zones. Additionally, there was positive feedback between the thaw subsidence of ground surface in the vicinity of the pipeline route and the thaw settlement of the pipeline foundation soils. The greater the earth surface subsidence, the more surface water ponding and soil disturbances, and even more progressive thawing. Therefore, some measures are recommended for stabilizing the pipeline foundation soils. The research results also indicate that the GPR method is effective, nondestructive, and convenient for evaluating the spatiotemporal extent and development processes of the freeze–thaw states of pipeline foundation soils and the underlying permafrost.

Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization

AbstractGround ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3 m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water‐filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9°C among degradation and stabilization stages and by 9.9°C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice‐poor transient layer, ice‐rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.

Recent Arctic tundra fire initiates widespread thermokarst development.

Fire-induced permafrost degradation is well documented in boreal forests, but the role of fires in initiating thermokarst development in Arctic tundra is less well understood. Here we show that Arctic tundra fires may induce widespread thaw subsidence of permafrost terrain in the first seven years following the disturbance. Quantitative analysis of airborne LiDAR data acquired two and seven years post-fire, detected permafrost thaw subsidence across 34% of the burned tundra area studied, compared to less than 1% in similar undisturbed, ice-rich tundra terrain units. The variability in thermokarst development appears to be influenced by the interaction of tundra fire burn severity and near-surface, ground-ice content. Subsidence was greatest in severely burned, ice-rich upland terrain (yedoma), accounting for ~50% of the detected subsidence, despite representing only 30% of the fire disturbed study area. Microtopography increased by 340% in this terrain unit as a result of ice wedge degradation. Increases in the frequency, magnitude, and severity of tundra fires will contribute to future thermokarst development and associated landscape change in Arctic tundra regions.

Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests

AbstractWe examined the effects of fire disturbance on permafrost degradation and thaw settlement across a series of wildfires (from ~1930 to 2010) in the forested areas of collapse‐scar bog complexes in the Tanana Flats lowland of interior Alaska. Field measurements were combined with numerical modeling of soil thermal dynamics to assess the roles of fire severity and climate history in postfire permafrost dynamics. Field‐based calculations of potential thaw settlement following the loss of remaining ice‐rich permafrost averaged 0.6 m. This subsidence would cause the surface elevations of forests to drop on average 0.1 m below the surface water level of adjacent collapse‐scar features. Up to 0.5 m of thaw settlement was documented after recent fires, causing water impoundment and further thawing along forest margins. Substantial heterogeneity in soil properties (organic layer thickness, texture, moisture, and ice content) was attributed to differing site histories, which resulted in distinct soil thermal regimes by soil type. Model simulations showed increasing vulnerability of permafrost to deep thawing and thaw settlement with increased fire severity (i.e., reduced organic layer thickness). However, the thresholds of fire severity that triggered permafrost destabilization varied temporally in response to climate. Simulated permafrost dynamics underscore the importance of multiyear to multidecadal fluctuations in air temperature and snow depth in mediating the effects of fire on permafrost. Our results suggest that permafrost is becoming increasingly vulnerable to substantial thaw and collapse after moderate to high‐severity fire, and the ability of permafrost to recover is diminishing as the climate continues to warm.

Stress and deformation characteristics of transmission tower foundations in permafrost regions along the Qinghai–Tibet Power Transmission Line

A transmission tower foundation embedded in frozen soil is subject to both the wind-induced uplift and frost heave forces. The frost heave results in an upward force acting on the foundation, while additional stress induced by the structure load may compress the underlying soils. The freezing- and thawing-induced deformations tend to cause further structural loads and lead to instability problems within the structure. To evaluate the engineering risk and ensure the safety of the Qinghai–Tibet Power Transmission Line (QTPTL) system, stress sensors were installed at the bases of two test tower foundations to investigate the stress state of the tower foundations. Using data on air and ground temperatures, and the deformation of tower foundations, we analyzed the stress variation, and the causes were discussed here. The results showed that the stresses at the bases of tower foundations had a close relationship with air and ground temperatures. The cooling of the underlying soils led to the occurrence of frost heave, which pushed the foundations upward and caused a significant stress bulb under the bases of tower foundations. Seasonal variations in the contact stress depended on the seasonal freezing and thawing of foundation soil. The contact stress increased with the cooling of the underlying soils and decreased with the warming of the underlying soils. The results also showed that the contact stress was free of the wind influence, i.e., the wind-induced uplift force was minor for the contact stress. To fully understand the influences of freezing and thawing on the stress state of tower foundations, a thermal–elasto-plastic finite element model for the tower foundation–soil system was established, and the stresses and deformations of a tower foundation subject to frost heave and thaw settlement were simulated. The results showed that the frost heave force induced by soil freezing potentially threatens the safety and normal operation of the QTPTL. Thaw settlement may lead to harmful deformation of tower foundations if global warming is considered in the numerical model. The remedial measure with thermosyphons only can reduce the settlement of the foundation and will increase the frost jacking risk of the foundation.

Thermal performance of a combined cooling method of thermosyphons and insulation boards for tower foundation soils along the Qinghai–Tibet Power Transmission Line

Preliminary field observations along the Qinghai–Tibet Power Transmission Line (QTPTL) show that foundation soils of some shallow footings (with an embedding depth of 3.7m) with thermosyphons in permafrost regions still suffer substantial and rapid thaw settlement in warm seasons. In this paper, a series of numerical simulations on the long-term thermal performance of foundation soils of these shallow footings are carried out. The simulated results show that thermosyphons could do effectively cool foundation soils at depths 2.5 to 8.0m under the footing. However, in warm season from mid-May to mid-October, the rapid warming of shallow foundation soils near the footing caused by heat transfer through the concrete footing could not be prevented. The maximum thaw around the footing could be as much as 1.0m deeper than that in the natural ground. Under a warming climate, the maximum thaw around the footing would go deeper than the embedding depth of the footing with four thermosyphons in very warm (≥−0.5°C) permafrost regions and with two thermosyphons in warm (≥−1.0°C) permafrost regions during a 50-year operational period. To retard thaw penetration around the footing, a combined cooling method of thermosyphons and insulation boards is proposed for foundation soils. Numerically simulated results show that the additional placement of the boards on ground surface could prevent the rapid warming of shallow foundation soils and effectively reduce the maximum thaw around the footing. The method could also effectively delay permafrost warming under the footing. Thus, it is recommended to be used at shallow footings in very warm, ice-rich permafrost regions along the QTPTL.

Freeze–thaw properties and long-term thermal stability of the unprotected tower foundation soils in permafrost regions along the Qinghai–Tibet Power Transmission Line

Many of the unprotected tower footings along the Qinghai–Tibet Power Transmission Line (QTPTL) were buried by open excavation in thaw-unstable permafrost. Their thermal stability was of concern due to climate warming and human-induced thermal disturbances. On the basis of ground temperature measurements during the last three years, the tower foundation soils were stable during the studied period from 2011 to 2013 in spite of appreciable impacts of engineering construction of tower footings on the thermal regimes of the surrounding and underlying permafrost. The thaw front near a typical concrete footing was 0.67m to 1.74m deeper than that at adjacent natural, undisturbed sites in summer, and ground temperatures near such footings were lower than those at nearby natural sites in winter. This thermal enhancement (TE) effect of concrete footings lengthened the duration of freezing and thawing of the surrounding soils, deepened the permafrost table near the tower foundations, and subsequently adversely affected the thermal stability of the tower foundation soils. Numerical modeling was used for simulating the long-term thermal stability of the foundations soils and impacts of the TE effect, ice contents, mean annual ground temperature (MAGT), embedding depths of tower footings, and climate warming on ground thermal regime. Under the scenario of climate warming by 2.6°C within the next 50years, the active layer thickens and permafrost temperatures at depths rise progressively with time. The ice contents and MAGT of permafrost remarkably would affect the degradation rate of permafrost around the footings. The TE effect of the footings thickened the active layer by at least 1m relative to natural sites 20-m away from the footings. The thaw settlement of tower foundation soils could present higher risk for the unprotected footings with a shallow (<5.8m) embedment in warm and ice-rich permafrost soils under a warming climate. In the end, some recommendations and suggestions were made.

INTEGRATED SAR TECHNOLOGIES FOR MONITORING THE STABILITY OF MINE SITES: APPLICATION USING TERRASAR-X AND RADARSAT-2 IMAGES

Abstract. The last three decades have seen significant mining development in the northern regions of Canada, where the freeze and thaw cycle of permafrost and corresponding surface subsidence and heave represent a significant challenge at all mining stages, from the design of infrastructures to the monitoring of restored areas. Over the past ten years, SAR interferometry has been widely used to monitor ground surface deformation. With this technique, changes in phase between two SAR acquisitions are used to detect centimetre to millimetre surface displacements over a large area with high spatial resolution. This paper presents the results of a project that aims to develop a SAR solution to provide useful information for environmental monitoring and assessing the stability of mining sites. RADARSAT-2 and TerraSAR-X images acquired during the summer of 2014 were used to measure the displacements of ground surface, infrastructures and stockpiles caused by seasonal changes in permafrost extent. The study area is an open-pit mine located in Nunavut, northern Canada, in the continuous permafrost zone. Results shown that surface displacements calculated from RADARSAT-2 and TerraSAR-X are very similar and in agreement with scientific and terrain knowledge. Significant displacements were observed in loose soil areas while none was detected in bedrock and rock outcrop areas. The areas most affected by active layer changes showed surface subsidence during the thaw settlement period. Thus, InSAR can be used as a tool to guide the siting and design of new infrastructure as well as highlighting risks in areas of unstable terrain.

Artificial ground freezing of fully saturated mucky clay: Thawing problem by centrifuge modeling

In the construction of cross passages in subway tunnels in soft soils having high water content and large void ratio, Artificial Ground Freezing (AGF) has been preferred due to its unique advantages as both a structural support and a water barrier. Compared to the freeze process, the thaw response is much more complicated and less research work has been documented, particularly in applicably predicting long-term settlement. It is mainly because of the variability in the redistribution of water released from melting ice crystals and the re-consolidation or over-consolidation circumstances during freeze. This paper is based on centrifuge modeling experiments to investigate the thaw settlement of the saturated mucky clay surrounding the subway tunnel. The experimental results demonstrated the significance of replicating the prototype self-weight stress condition in a model to evaluate the thaw settlement of Shanghai mucky clay after artificial ground freezing. The water content profiles of model soils presents that there was still serious water content re-distribution even after freeze–thaw. It indicates the potential reason of differential settlement along subway tunnel around AFG construction site. Great increase in permeability of mucky clay also makes clear sense for additional large thaw settlement after artificial ground freezing. More importantly, field self-weight stress condition extended the influence area of moisture migration and aggravated the pore size to be concentrated in coarser field. All the discussion revealed that the advantages of centrifugal modeling in thaw problem by providing field self-weight. Additionally in the further computation model development, large strain thaw consolidation theory should be applied to prognosticate the long-term settlement of thick soft mucky clay after artificial ground freezing construction. Finally the scaling laws generally used in thaw processes were also checked in this paper in consideration of lacking references on thaw problem in centrifuge models.

Centrifuge experimental study of thaw settlement characteristics of mucky clay after artificial ground freezing

Artificial ground freezing (AGF) plays a significant role in the construction of subway tunnel cross passages, underground commercial streets and underground pumping stations, etc. especially under adverse hydro-geological conditions. Associated with the properties of high water content and large void ratio in saturated Shanghai mucky clay, large thaw settlement has arisen after AGF construction. The thawing response is much more complicated compared to freezing and less research work has been documented in the AGF method partly due to the long-period and variability in the redistribution of water released from melting ice crystals and the rewetting of the soil aggregates in clay. This paper presented a series of centrifuge model tests to derive the thawing function development and predict the thaw settlement. The results show that the thawing rate was distinct and larger than the conventional results of small sample tests without stress acting. The thawing front advanced much faster compare to the development in natural frozen soil. An improved gray prediction model emphasizes that a simple analytical result with new thaw front function is much consistent with the experimental and prediction results. All the discussions demonstrate that small scale specimen thaw test at 1g is not capable to directly apply into full scale prediction of the thaw settlement in thick soft saturated clay after artificial ground freezing construction, in which self-weight dominates the process of consolidation. This could motivate, in the near future of computation model development, that the large strain thaw consolidation theory should be applied to prognosticate the long-term settlement of thick soft mucky clay after artificial ground freezing construction.

Thermal-Hydro-Mechanical Analysis of Frost Heave and Thaw Settlement

AbstractFrost heave and thaw settlement are the cause of substantial damage to infrastructure in regions of seasonal freezing as well as seasonal thawing (permafrost). While frost heaving of soils has been researched for decades, less attention has been paid to quantitative estimates of settlement and loss of strength of soils due to thawing. A constitutive model is developed, capable of simulating freezing and thawing of soils, and associated changes in the soil strength. While the porosity growth parameters describing frost heaving have been calibrated and validated for a specific soil, the description of the thawing phase has not been validated due to a lack of experimental data. The yielding of the frozen soil is described using the critical state concept, with the pore ice content being an important parameter affecting the yield function. The model was calibrated using available laboratory test data and used in the simulation of a freezing–thawing cycle in the soil with embedded footing.

Observing Muostakh disappear: permafrost thaw subsidence and erosion of a ground-ice-rich island in response to arctic summer warming and sea ice reduction

Abstract. Observations of coastline retreat using contemporary very high resolution satellite and historical aerial imagery were compared to measurements of open water fraction, summer air temperature, and wind. We analysed seasonal and interannual variations of thawing-induced cliff top retreat (thermo-denudation) and marine abrasion (thermo-abrasion) on Muostakh Island in the southern central Laptev Sea. Geomorphometric analysis revealed that total ground ice content on Muostakh is made up of equal amounts of intrasedimentary and macro ground ice and sums up to 87%, rendering the island particularly susceptible to erosion along the coast, resulting in land loss. Based on topographic reference measurements during field campaigns, we generated digital elevation models using stereophotogrammetry, in order to block-adjust and orthorectify aerial photographs from 1951 and GeoEye, QuickBird, WorldView-1, and WorldView-2 imagery from 2010 to 2013 for change detection. Using sea ice concentration data from the Special Sensor Microwave Imager (SSM/I) and air temperature time series from nearby Tiksi, we calculated the seasonal duration available for thermo-abrasion, expressed as open water days, and for thermo-denudation, based on the number of days with positive mean daily temperatures. Seasonal dynamics of cliff top retreat revealed rapid thermo-denudation rates of −10.2 ± 4.5 m a−1 in mid-summer and thermo-abrasion rates along the coastline of −3.4 ± 2.7 m a−1 on average during the 2010–2013 observation period, currently almost twice as rapid as the mean rate of −1.8 ± 1.3 m a−1 since 1951. Our results showed a close relationship between mean summer air temperature and coastal thermo-erosion rates, in agreement with observations made for various permafrost coastlines different to the East Siberian Ice Complex coasts elsewhere in the Arctic. Seasonality of coastline retreat and interannual variations of environmental factors suggest that an increasing length of thermo-denudation and thermo-abrasion process simultaneity favours greater coastal erosion. Coastal thermo-erosion has reduced the island's area by 0.9 km2 (24%) over the past 62 years but shrank its volume by 28 x 106 m3 (40%), not least because of permafrost thaw subsidence, with the most pronounced with rates of &amp;amp;geq;− 11 cm a−1 on yedoma uplands near the island's rapidly eroding northern cape. Recent acceleration in both will halve Muostakh Island's lifetime to less than a century.

An experimental study on the mechanical properties of silty soils under repeated freeze–thaw cycles

In this study, the subgrade fill material from the Nagqu Logistics Center Yard (NLCY) along the Qinghai–Tibet Railway was investigated. And the thaw subsidence properties and dynamic properties were thoroughly analysed in laboratory tests.1)From the determined thaw subsidence properties, the following results were obtained: samples with a higher degree of compactness exhibited heave deformation, whereas those with a lower degree of compactness exhibited compressive deformation after repeated freeze–thaw cycles. However, there is a critical compactness level at which the height of the samples does not change after repeated freeze–thaw cycles. The consolidation effect of the load restrains frost heave deformation; however, the amount of thaw subsidence deformation increases. The thaw subsidence ratio first increases, then decreases and becomes steady after the fifth freeze–thaw cycle as the number of freeze–thaw cycles increases. It is recommended that the thaw subsidence properties of silty soils be assessed after 5–6 freeze–thaw cycles.2)From the determined dynamic properties, the following results were obtained: the dynamic stress vs. strain curves clearly show a nonlinear trend. The dynamic modulus greatly decreases, whereas the damping ratio increases with additional freeze–thaw cycles; and changes level off after the sixth freeze–thaw cycle; the dynamic properties after 6–7 freeze–thaw cycles are suggested for use in designing and calculating indexes. Moreover, the dynamic modulus increases and the damping ratio decreases as the confining pressure and compactness increase.

Experimental and Theoretical Investigations on Frost Heave in Porous Media

For the construction in cold regions, frost heave and thaw settlement are the two factors which must be taken care of. Considered that a saturated soil column was subjected to an overburden pressure to model the ice lens growing process. A typical process, which coupled water, heat, and stress that happened in a saturated freezing soil column, was simulated by the finite element software. We did the numerical simulation under the same conditions as the experiment tests and then compared the results from temperature, frost heave, frozen structure, water content, and water intake. Result shows that the simulation results match well with the experimental results, and the correctness of the mathematical model is validated. On that basis, frost heave amount under different conditions by changing the temperature boundary and loading boundary is obtained. The frost heave has an optimum temperature gradient. Under the optimum value, the frost heave amount increases with increasing temperature gradient. Above the optimum value, frost heave decreases with increasing temperature gradient. Increasing the overburden pressure, frost heave amount always decreases. These results can provide references for the constrictions in cold regions.