Freeze-thaw Erosion Research Articles

Using Advanced InSAR Techniques and Machine Learning in Google Earth Engine (GEE) to Monitor Regional Black Soil Erosion—A Case Study of Yanshou County, Heilongjiang Province, Northeastern China

The black soil region experiences complex erosion due to natural processes and intense human activities, leading to soil degradation and adverse ecological and agricultural impacts. However, the complexities involved in quantifying regional erosion poses remarkable challenges in accurately assessing the current status of regional soil erosion for effective soil conservation. To solve this issue, we proposed a new method for monitoring soil erosion using Interferometric synthetic aperture radar (InSAR) technology and machine learning algorithms within the Google Earth Engine platform. The new method not only enables regional-scale monitoring, but also ensures high accuracy in measurement (millimeter-level). The erosion susceptibility of the study area (Yanshou County, Heilongjiang Province, Northeastern China) was also classified using random forest algorithms to refine the monitored and predicted soil erosion. The results indicate that the five-year (2016–2021) deformation in Yanshou County was −11.08 mm, with a significant mean cumulative deformation of −8.08 mm yr−1 occurring in 2017. The driving factor analysis shows that the region was subject to the compound effect of water and freeze–thaw erosion, closely related to crop phenological stages. The susceptibility analysis indicates that 73.3% of the region was susceptible to erosion, with a higher probability in river areas, at high altitudes, and on steep slopes. However, good vegetation cover can reduce the risk of soil erosion to some extent. This study offers a new perspective on monitoring regional soil erosion in the black soil region of China. The proposed method holds potential for future expansion to monitor soil erosion in a larger areas, thereby guiding the strategies development for protection of the agriculturally important black soil.

Spatial and temporal distribution and environmental determinants of freeze-thaw erosion intensity in Qiangtang grasslands, China

Context Analysing freeze-thaw erosion is of great significance to ecological environment protection and land resource utilisation in high altitude areas. Aims We used seven indicators (temperature, precipitation, vegetation cover, elevation, slope, slope orientation, and sand content) to calculate the freeze-thaw erosion intensity index for different seasons from 2000 to 2019. Methods We used a graded weighted evaluation model and a geographical detector method to analyse spatiotemporal pattern and driving factors of freeze-thaw erosion intensity in Qiangtang grasslands. Key results (1) From 2000 to 2019, the total area of freeze-thaw erosion was higher in the non-growing season than in the growing season. The area of moderate and above-average freeze-thaw erosion increased over time in the non-growing season but decreased in the growing season. The spatial distribution of freeze-thaw erosion was mainly determined by the annual range of precipitation and temperature, which reflect the intensity and frequency of freezing and thawing cycles. (2) Vegetation cover was an indirect factor that influenced the soil moisture and stability. The slope was another important factor that affected the spatial distribution of freeze-thaw erosion in different regions. Conclusions The results show that in 2000–2019 the area of freeze-thaw erosion showed a downward trend. The erosion degree in the non-growing season is on the rise. Implications Our study provides new insights into the dynamics and mechanisms of freeze-thaw erosion in Qiangtang grasslands and contributes to the understanding and management of water and climate change impacts on this region.

Investigation on damage evolution mechanism of various FRP strengthened concrete subjected to chemical-freeze-thaw coupling erosion.

The corrosion resistance of FRP-reinforced ordinary concrete members under the combined action of harsh environments (i.e., alkaline or acidic solutions, salt solutions) and freeze-thaw cycles is still unclear. To study the mechanical and apparent deterioration of carbon/basalt/glass/aramid fiber cloth reinforced concrete under chemical and freeze-thaw coupling. Plain concrete blocks and FRP-bonded concrete blocks were fabricated. The tensile properties of the FRP sheet and epoxy resin sheet before and after chemical freezing, the compressive strength of the FRP reinforced test block, and the bending capacity of the prismatic test block pasted with FRP on the prefabricated crack side were tested. The deterioration mechanism of the test block was analyzed through the change of surface photos. Based on the experimental data, the Lam-Teng constitutive model of concrete reinforced by alkali-freeze coupling FRP is modified. The results indicate that, in terms of apparent properties, with the increase in the duration of chemical freeze-thaw erosion, the surface of epoxy resin sheets exhibits an increase in pores, along with the emergence of small cracks and wrinkles. The texture of FRP sheets becomes blurred, and cracks and wrinkles appear on the surface. In terms of failure modes, as the number of chemical coupling erosion cycles increases, the location of failure in epoxy resin sheets becomes uncertain, and the failure plane tilts towards the direction of the applied load. The failure mode of FRP sheets remains unchanged. However, the bonding strength between FRP sheets and concrete decreases, resulting in a weakened reinforcement effect. In terms of mechanical properties, FRP sheets undergo the most severe degradation in the coupled environment of acid freeze-thaw cycles. Among them, GFRP experiences the largest degradation in tensile strength, reaching up to 30.17%. In terms of tensile performance, the sheets rank from highest to lowest as follows: CFRP, BFRP, AFRP, and GFRP.As the duration of chemical freeze-coupled erosion increases, the loss rate of compressive strength for specimens bonded with CFRP is the smallest (9.62% in salt freeze-thaw environment), while the loss rate of bearing capacity is higher for specimens reinforced with GFRP (33.8% in acid freeze-thaw environment). In contrast, the loss rate of bearing capacity is lower for specimens reinforced with CFRP (13.6% in salt freeze-thaw environment), but still higher for specimens reinforced with GFRP (25.8% in acid freeze-thaw environment).

Engineering Properties and Microstructure of Soils Stabilized by Red-Mud-Based Cementitious Material.

Red mud (RM) is an industrial waste generated in the process of aluminum refinement. The recycling and reusing of RM have become urgent problems to be solved. To explore the feasibility of using RM in geotechnical engineering, this study combined magnesium oxide (MgO) (or calcium oxide (CaO)) with RM as an RM-based binder, which was then used to stabilize the soil. The physical, mechanical, and micro-structural properties of the stabilized soil were investigated. As the content of MgO or CaO in the mixture increased, the unconfined compressive strength (UCS) of the RM-based cementitious materials first increased and then decreased. For the soils stabilized with RM-MgO or RM-CaO, the UCS increased and then decreased, reaching a maximum at RM:MgO = 5:5 or RM:CaO = 8:2. The addition of sodium hydroxide (NaOH) promoted the hydration reaction. The UCS enhancement ranged from 8.09% to 66.67% for the RM-MgO stabilized soils and 204.6% to 346.6% for the RM-CaO stabilized soils. The optimum ratio of the RM-MgO stabilized soil (with NaOH) was 2:8, while that of the RM-CaO stabilized soil (with NaOH) was 4:6. Freeze-thaw cycles reduced the UCS of the stabilized soil, but the resistance of the stabilized soil to freeze-thaw erosion was significantly improved by the addition of RM-MgO or RM-CaO, and the soil stabilized with RM-MgO had better freeze-thaw resistance than that with RM-CaO. The hydrated magnesium silicate generated by the RM-MgO stabilized soil and the hydrated calcium silicate generated by the RM-CaO stabilized soil helped to improve the UCS of the stabilized soil. The freeze-thaw cycles did not weaken the formation of hydration products in the stabilized soil but could result in physical damage to the stabilized soils. The decrease in the UCS of the stabilized soil was mainly due to physical damage.

Spatiotemporal Distribution Characteristics and Influencing Factors of Freeze–Thaw Erosion in the Qinghai–Tibet Plateau

Freeze–thaw (FT) erosion intensity may exhibit a future increasing trend with climate warming, humidification, and permafrost degradation in the Qinghai–Tibet Plateau (QTP). The present study provides a reference for the prevention and control of FT erosion in the QTP, as well as for the protection and restoration of the regional ecological environment. FT erosion is the third major type of soil erosion after water and wind erosion. Although FT erosion is one of the major soil erosion types in cold regions, it has been studied relatively little in the past because of the complexity of several influencing factors and the involvement of shallow surface layers at certain depths. The QTP is an important ecological barrier area in China. However, this area is characterized by harsh climatic and fragile environmental conditions, as well as by frequent FT erosion events, making it necessary to conduct research on FT erosion. In this paper, a total of 11 meteorological, vegetation, topographic, geomorphological, and geological factors were selected and assigned analytic hierarchy process (AHP)-based weights to evaluate the FT erosion intensity in the QTP using a comprehensive evaluation index method. In addition, the single effects of the selected influencing factors on the FT erosion intensity were further evaluated in this study. According to the obtained results, the total FT erosion area covered 1.61 × 106 km2, accounting for 61.33% of the total area of the QTP. The moderate and strong FT erosion intensity classes covered 6.19 × 105 km2, accounting for 38.37% of the total FT erosion area in the QTP. The results revealed substantial variations in the spatial distribution of the FT erosion intensity in the QTP. Indeed, the moderate and strong erosion areas were mainly located in the high mountain areas and the hilly part of the Hoh Xil frozen soil region.

Effects of freeze–thaw on bank soil mechanical properties and bank stability

Riverbank instability in the seasonally frozen zone is primarily caused by freeze–thaw erosion. Using the triaxial freeze–thaw test on the bank of Shisifenzi Bend in the Yellow River section of Inner Mongolia, we investigated the changes in the mechanical properties of the soil at different freezing temperatures and freeze–thaw times, and analyzed the bank’s stability before and after freezing based on the finite element strength reduction method. The results showed that the elastic modulus, cohesion, internal friction angle and shear strength of the soil tended to decrease with the increase in the number of freeze–thaw cycles and the decrease in freezing temperature. After 10 freezing cycles at − 5 ℃, − 10 ℃, − 15 ℃ and − 20 ℃, the modulus of elasticity of soil decreased by 40.84 ~ 68.70%, the cohesion decreased by 41.96 ~ 56.66%, the shear strength decreased by 41.92 ~ 57.32%, respectively. Moreover, the stability safety coefficient of bank slope decreased by 18.58% after freeze–thaw, indicating that the freeze–thaw effect will significantly reduce the stability of bank slope, and the bank slope is more likely to be destabilized and damaged after freeze–thaw.

Study on sulfate diffusion test and mathematical model of manufactured sand concrete under typical freeze-thaw environment in Northwest China

In the construction industry, it is imperative to replace natural sand with manufactured sand. The environment in northwest China is very complex and harsh. The application of manufactured sand concrete in such a harsh environment needs scientific and comprehensive research to meet the requirements. However, there is a gap in the study of sulfate freeze-thaw resistance of manufactured sand concrete in the complex environment of Northwest China. Therefore, this study investigated the northwest environment, designed an indoor sulfate freeze-thaw cycle experiment system close to the real environment, and designed a conductive titration method to test the sulfate ion content in hardened concrete. The influence of the freeze-thaw cycle on the diffusion depth of sulfate ions in manufactured sand concrete was studied. Finally, the following conclusions are obtained: In the process of conductometric titration, hydrochloric acid is used as the dissolution solution, Ag2O and CO2 are used as neutralizers, and Ba(NO3)2 is used as the titration solution, which can perfectly eliminate the significant influence ions in the test solution, and can accurately test the content of sulfate ions in hardened concrete. The sulfate ion content of concrete at different depths was tested, and it was found that the two sides of sulfate erosion caused by freeze-thaw cycles were mainly reflected in about 100 freeze-thaw cycles. The limit number of freeze-thaw cycles N0 and the limit diffusion depth X0 are proposed, and the diffusion equation of manufactured sand concrete under the action of sulfate freeze-thaw cycles is derived. The proposed diffusion parameter v is unique to the concrete, which can well judge the sulfate freeze-thaw resistance of the concrete. When v is closer to 0, it shows that the resistance of concrete to sulfate freeze-thaw erosion is better. For the northwest environment of China, the manufactured sand concrete should ensure v < 6; the environment in Northwest China has a very complex multi-factor erosion environment. It is worth noting that this study is only applicable to laboratory conditions. To improve the accuracy and reference value of experimental research, future research needs to add more comprehensive environmental impact factors and collect actual data in the northwest environment of China for verification.

Extreme climate and human activities contribute to low-frequency, large-scale catastrophic debris flow: a case study in the Heishui Gully

Rainfall is an excitation factor for rainfall-type debris flows, and high-frequency rainfall commonly does not directly trigger large-scale catastrophic debris flows. A low-frequency, large-scale catastrophic debris flow occurred in Heishui Gully (HSG), Pingwu County, Sichuan Province, southwestern China on 12 July 2022. In this study, the HSG debris flow was used as a case study to reveal the formation mechanisms of low-frequency and large-scale catastrophic debris flow triggered by high-frequency gentle rainfall by calculating and analysing a total of five indicators, including the Standard Precipitation Index (SPI), the Freeze-Thaw Index (FTI), the empirical relationship between earthquakes and landslides, the hypsometric integral (HI) and human activities. The study results indicate that high-frequency gentle rainfall is a direct factor in the debris flow outbreak in HSG. Long-duration extreme drought conditions and extreme freeze-thaw erosion provided sufficient soil conditions for debris flow formation. Frequent earthquakes and mature erosional geomorphologic evolution have indirectly contributed to the debris flow formation. Simultaneously, human activities downstream of HSG amplified the risk of debris flow disaster. The results reveal the contribution of extreme climates and human activities to low-frequency, large-scale catastrophic debris flows initiated by high-frequency gentle rainfall, which is significant for accurately assessing and predicting debris flow occurrence.

A novel method for analyzing the spatial and temporal distribution of freeze-thaw erosion based on a similar information value model: a case study of the China-Mongolia-Russia Economic Corridor region

In this study, the region along the Mongolia-China-Russia Economic Corridor was selected as the subject. Here, a freeze-thaw erosion model would be built and used. By contrasting the probability of a geological disaster under the effect of an influencing factor with the probability of a geological disaster in the whole research region, the information value model is realized. In order to identify the most prone factors of freeze-thaw erosion in the research region, we replaced the possibility of geological disasters with the possibility of freeze-thaw erosion. The study region under each influencing factor was separated into five grades. Each grade’s information value was computed using the principles of the information quantity model and the freezing and thawing erosion grade division. Since there were positive and negative information values, for the purposes of calculating probabilities, they were normalized to obtain the similar information value for each grade before calculating the overall similar information value of each factor. The similar information value model (SIVM) underlies this procedure determines the weight. We compared the Analytic Hierarchy Process (AHP) and SIVM with the results of 0.070–0.758 and 0.063–0.776, respectively. Finally, the outcomes were confirmed through visual interpretation.

Energy evolution and crack development characteristics of sandstone under freeze-thaw cycles by digital image correlation.

Freeze-thaw erosion is the main reason for rock mass instability in cold regions and poses major threats to public safety. In this study, the stress threshold, energy, and strain field evolution of sandstone and the variation in stress intensity factor of fractures in various stress fields were all investigated after freeze-thaw cycles by uniaxial compression tests and digital image correlation technology. The results show that the elastic modulus, crack initiation stress, and peak stress all fell by 97%, 92.5%, and 89.9%, respectively, as the number of freeze-thaw cycles approaches 80. Elastic energy's storage capacity also dropped from 0.85 to 0.17. Sandstone's strain was increased by freeze-thaw erosion, which also improved ductility and shortened the cracking time. The stress intensity factor at the crack tip was positively correlated with the tip inclination angle and negatively correlated with the number of freeze-thaw cycles. This study provides a useful reference for understanding the stability of rock masses and the characteristics of crack derivation in cold regions.

Quantifying the effect of a retrogressive thaw slump on soil freeze–thaw erosion in permafrost regions on the Qinghai–Tibet Plateau, China

AbstractThermokarst terrain is developing at an accelerating pace in the ice‐rich permafrost on the Qinghai–Tibet Plateau (QTP), China, and the most dramatic of these terrain‐altering thermokarsts is retrogressive thaw slump (RTS). The freeze–thaw erosion (FTE) impacts are sharply increasing on the Plateau due to RTS, especially as a result of the migration of fine sediments in cold climates, these impacts are still not quantified due to the limitation of hydro‐thermal‐mass transport laws in RTS development. Moreover, it is difficult to assess the impact of RTS on the ecology and environment, especially on soil erosion. This study developed a heat–water‐mass transport coupled model of a RTS in the Beiluhe River Region on the QTP, considering the actual topography, water‐ice phase change, latent heat, and surface heat exchange layer. Based on the observed data of ground temperature, unfrozen water content, and heat flux, the coupled model herein is practicable for presenting the geotemperature regime and groundwater flow in the RTS area, thereby quantifying the ice‐rich permafrost thaw and mass wasting. The results presented indicate that: (1) the seepage velocity of the superficial zone (0–1.5 m depth) is two orders of magnitude higher than that of the permafrost table; (2) the mean ice‐rich permafrost thaw volume was 13.4 m2 from 2016 to 2021; and (3) the cumulative mass transport volume was 22 m2 from July 2020 to September 2021. In addition, the relation between the FTE (shown as the migration of sediments) and the amount of ground ice ablation can be fitted by an exponential equation. This work proposes a reliable method for quantifying the effect of FTE and is helpful to assess the eco‐environmental impacts of RTS.

Spatiotemporal variations of freeze-thaw erosion risk during 1991–2020 in the black soil region, northeastern China

Freeze-thaw (FT) erosion, which occurs in high-altitude and high-latitude regions, has a considerable impact on water and wind erosion. However, studies on long-term variations of FT erosion induced risks are still limited. In the present study, based on 30-year data at 247 meteorological stations, spatiotemporal FT erosion risk in the black soil region, northeastern China was evaluated through the Analytical Hierarchy Process (AHP) and Entropy-weight method (EWM). Six FT erosion-related variables, including annual FT cycle days, soil water content (SWC), fraction vegetation coverage (FVC), slope, soil bulk density (BD), and soil structural stability (SSI) were used to assess FT erosion risk in the study region. Among these variables, the slope was the most important variable (45 %), followed by annual FT cycle days (15 %), FVC (15 %), and SSI (14 %). FT erosion risk differed in different land use types. Woodland, residential land and grassland suffered severe FT erosion risk, and paddy and dryland suffered slight FT erosion risk. Complex topography areas had a higher FT erosion risk. During past 30 years, global warming mitigated the FT erosion risk. This study can help understand soil erosion characteristics and soil loss control for the Chinese black soil region and similar regions in the world.

Analysis of eccentrically loaded FRP partially wrapped reinforced concrete columns subjected to combined environmental erosion

The behavior of eccentrically loaded fiber reinforced polymer (FRP) partially wrapped reinforced concrete (RC) columns under combined environmental erosion was investigated in this paper. Circular RC columns were firstly subjected to chloride erosion where the target corrosion degree (0, 10 %, and 20 %) is obtained with externally applied current. This was then followed by partially strengthening with 2-ply of glass fiber reinforced polymer (GFRP) strips as well as 50 freeze–thaw cycles. Series of eccentric compression tests were conducted with ranging eccentricities of 0, 5 mm, 10 mm, and 15 mm. For comparison, the carbon fiber reinforced polymer (CFRP) partially strengthened columns with the corrosion degree of 10 % and subjected to 50 freeze–thaw cycles were also eccentrically loaded with an eccentricity of 10 mm. Results showed that with increasing corrosion degree, the bearing capacity of GFRP strengthened column showed a 2-stage behavior (firstly increased and then decreased), which may be caused by the confinement reduction of FRP on columns due to severe environmental erosion. Under small eccentric loading, The CFRP strengthened RC columns showed better compressive behavior than that of GFRP strengthened RC columns. Based on the stress–strain relationship of constituent materials, a simplified analytical model considered the effects of chloride and freeze–thaw erosion was put forward to predict the bearing capacity of FRP partially wrapped RC column under eccentric loading.

Study on the pore structure characteristics and damage constitutive model of sandstone under freeze-thaw conditions

Rocks in Northwest China are often affected by the combined action of freeze-thaw and load erosion. Therefore, in order to better understand the mechanical properties of rocks in seasonal frozen areas and the meso-damage caused by freeze-thaw erosion, uniaxial compression tests, electron microscope scanning tests, X-ray diffraction tests (XRD) and mercury intrusion tests (MIP) were carried out on five sandstone samples with different freeze-thaw times, and the mechanical parameters and meso-damage characteristics of sandstone samples with different freeze-thaw times were obtained. Fractal theory was used to analyze the change in pore volume of sandstone after freeze-thaw cycles. Finally, the damage constitutive equation under the coupling action of freeze-thaw damage and load was established based on Lemaitre’s equivalent effect variation criterion. The results showed that the type of sandstone is a porous coarse-grained sandstone. With the increased freeze-thaw times, the compressive strength and cohesion of sandstone gradually decreased, and the closed pores in sandstone gradually connected, leading to the visible internal macroscopic cracks. Affected by freeze-thaw times, the volume proportion of large pores (100–1,000 µm) in sandstone gradually increased, while the volume proportion of micropores (.05–100 µm) gradually decreased. With the increased freeze-thaw times, the fractal dimension of pore volume decreased from 1.94 to 1.59. The theoretical curve can better fit the characteristic points of the stress-strain curve, which can further reveal the damage mechanism of sandstone under the coupling effects of freeze-thaw and load. The minimum error between the peak point of the experimental curve and the theoretical curve is 3.3%.

Freeze-thaw erosion mechanism and preventive actions of highway subgrade soil in an alpine meadow on the Qinghai-Tibet Plateau

Freeze-thaw erosion is widely distributed in China, where the difference of natural conditions brings a series of characteristics for different regions. The alpine meadow area of the Qinghai-Tibet Plateau (QTP) has a special climate, geography, and hydrogeology environment, with multiple road frost heaves and frost boiling failures, which seriously threaten the highway constructions in the QTP. This study summarizes the freeze–thaw geology of the southeastern QTP. For the highway constructions in the frozen soil areas, multiple problems such as frost heave, thawing settlement, freeze–thaw weathering, and pavement cracks and highway operation and management issues may rise as a result of the activity of the freeze–thaw geology, which damages the subgrade structure. To prevent the occurrence of possible hazards and reduce hazards and risks, this study discusses a series of countermeasures and suggestions. A case history is referred to, specifically the Budongquan highway in the QTP, where the study section is conducted, to evaluate the effectiveness of the adopted treatment measures. The results show that these treatment measures effectively prevent the surface water from infiltrating into the subgrade in the rainy season, block the migration of groundwater to the upper subgrade during the freezing season, and discharge the water accumulated in the subgrade as soon as possible after thawing. Thus, this study further understanding of the long-term durability and stability of subgrade, and provide useful information for the structure design of the highway subgrade in cold regions.

Evaluating the sensitivity and influential factors of freeze-thaw erosion in Tibet, China

Freeze‒thaw (FT) erosion has gradually become more severe due to climate warming, and concerns about FT erosion in ecologically fragile areas (e.g., high-altitude and high-latitude areas) continues to grow. Tibet, located at the Third Pole of Earth, is also in a substantial part underlain with seasonally frozen soil and subject to FT erosion. Evaluating the sensitivity and influential factors of FT erosion in Tibet is warranted to manage the ecological environment and human production activities. In this study, we investigated the sensitivity and spatial distribution characteristics of FT erosion in Tibet based on advanced remote sensing and geographic information system (GIS) technologies. To further explore the influence of each factor on FT erosion, we analyzed the sensitivity of FT erosion under each factor condition. Our results showed that the annual temperature range is the most influential factor on FT erosion among temperature, precipitation, topography and vegetation. In addition, we introduced the coefficient of variation (CV) to represent the stability of temperature and then used CMIP5 simulation data to estimate the susceptibility of FT erosion in Tibet over the next 30 years. The CVs in central and western Tibet were higher than those in other areas and thus need more attention to FT erosion in central and western Tibet in the future.

Compressive behavior of GFRP partially strengthened corroded RC columns subjected to freeze-thaw erosion

The compression test of glass fiber-reinforced polymer (GFRP) partially strengthened corroded reinforced concrete (RC) columns subjected to freeze-thaw cycling was conducted in this study. A total of 45 small-scale RC columns were prepared. The columns were firstly subjected to accelerated corrosion conditioning to obtain the target level of steel loss, and then partially strengthened with 2-ply GFRP strips; finally, the strengthened RC columns were subjected to different freeze-thaw cycles. The main parameters in this experiment were reinforcement corrosion degree (0, 10%, and 20%) and number of freeze-thaw cycles (0, 25, 50, and 75). The compressive behaviors of columns were evaluated in terms of failure mode, load capacity, load-displacement response, stiffness, and ductility. Results showed that GFRP partially strengthening could significantly improve the load capacity, stiffness, and ductility of corrosion-damaged RC columns, while the ultimate load capacity and stiffness of strengthened columns decreased with the increase of freeze-thaw cycles. Moreover, a design-oriented calculation method for the ultimate load capacity of GFRP partially strengthened corroded RC columns subjected to freeze-thaw cycles was proposed and validated by the experimental results.

137Cs tracing of the spatial patterns in soil redistribution, organic carbon and total nitrogen in the southeastern Tibetan Plateau

The southeastern Tibetan Plateau, which profoundly affects East Asia by helping to maintain the stability of climate systems, biological diversity and clean water, is one of the regions most vulnerable to water erosion, wind erosion, tillage erosion, freeze–thaw erosion and overgrazing under global climate changes and intensive human activities. Spatial variations in soil erosion in terraced farmland (TL), sloping farmland (SL) and grassland (GL) were determined by the 137Cs tracing method and compared with spatial variations in soil organic carbon (SOC) and total nitrogen (total N). The 137Cs concentration in the GL was higher in the 0–0.03 m soil layer than in the other soil layers due to weak migration and diffusion under low precipitation and temperature conditions, while the 137Cs concentration in the soil layer of the SL was generally uniform in the 0–0.18 m soil layer due to tillage-induced mixing. Low 137Cs inventories appeared at the summit and toe slope positions in the SL due to soil loss by tillage erosion and water erosion, respectively, while the highest 137Cs inventories appeared at the middle slope positions due to soil accumulation under relatively flat landform conditions. In the GL, the 137Cs data showed that higher soil erosion rates appeared at the summit due to freeze–thaw erosion and steep slope gradients and at the toe slope position due to wind erosion, gully erosion, freeze–thaw erosion and overgrazing. The 137Cs inventory generally increased from upper to lower slope positions within each terrace (except the lowest terrace). The 137Cs data along the terrace toposequence showed abrupt changes in soil erosion rates between the lower part of the upper terrace and the upper part of the immediate terrace over a short distance and net deposition on the lower and toe terraces. Hence, tillage erosion played an important role in the soil loss at the summit slope positions of each terrace, while water erosion dominantly transported soil from the upper terrace to the lower terrace and resulted in net soil deposition on the flat lower terrace. The SOC inventories showed similar spatial patterns to the 137Cs inventories in the SL, TL and GL, and significant correlations were found between the SOC and 137Cs inventories in these slope landscapes. The total N inventories showed similar spatial patterns to the inventories of 137Cs and SOC, and significant correlations were also found between the total N and 137Cs inventories in the SL, TL and GL. Therefore, 137Cs can successfully be used for tracing soil, SOC and total N dynamics within slope landscapes in the southeastern Tibetan Plateau.

Study on Stability Analysis of Soil-Rock-Mixture Slopes under Freeze-Thaw Erosion in Greater Khingan Mountains

Abstract Under the action of freeze-thaw erosion, slopes in permafrost regions frequently suffer from geological disasters. The unique properties of soil-rock-mixture slopes further complicate this freeze-thaw stability problem. To study the effects of freeze-thaw erosion on the stability of soil-rock-mixture slopes, several indoor tests were first carried out on the specimens collected from the target bare slope at the K105+750~K105+850 section of the Ali River to the Kubuchun Forest Farm along National Highway 332 in permafrost regions of Greater Khingan Mountains, and then, according to the test results, damage theory, strength reduction method, Python script, and ABAQUS numerical analysis software, the slippage and safety factor of the bare slope under freeze-thaw cycles were obtained, and finally, the damage degree of freeze-thaw erosion to the bare slope was quantified. To improve the stability of bare slope in the freeze-thaw environment, the composite ecological slope protection measures of arched skeleton + three-dimensional net + grass planting were finally selected, and its feasibility is verified with the help of on-site monitoring and numerical simulation; then, the long-term freeze-thaw stability of the slope after revetment was studied. Key findings indicated that (1) the threshold between soil and rock in the target slope was 5 mm, the soil-to-rock mass and volume ratios of the slope were 55.04% : 44.96% and 69.38% : 30.62%, respectively. (2) After the 150 freeze-thaw cycles, the peak strength and elastic modulus of the specimens decreased 59.7% and 79.50%, respectively. (3) Meanwhile, the freeze-thaw damage was 0.79. (4) The slope safety factor was inversely proportional to the number of freeze-thaw cycles. The target bare slope was unstable after 150 freeze-thaw cycles, and the safety stability reduction rate was 41%. (5) Compared with the bare slope, the shallow horizontal slip of the slope after revetment decreased from 1.528 m to 4.971 cm, and the slope safety factor increased from 0.997 to 4.501, which shows that the slope protection measures are initially feasible. In addition, the numerical analysis results are consistent with the field monitoring data, and the error between the two is ≤2.01%, which proves the rationality of the numerical model established in this paper and provides data support for subsequent research.

Service Life Prediction of Basalt Fiber Reinforced Concrete under Salt Freeze-thaw Cycles

To address the reduced durability of concrete structures under salt freeze-thaw erosion in Northwest China, basalt fiber reinforced concrete and common concrete with different mixing amounts were selected to predict their service life in three freeze-thaw conditions. Results showed that the damage on concrete under fresh water freeze-thaw condition is lower than that caused by salt freeze-thaw erosion, the addition of basalt fiber can effectively slow down the degradation of mechanical properties of concrete under salt freeze-thaw erosion, and the lowest degradation rate is reached when the content of basalt fiber is 0.15%. Fiber hinders the expansion of cracks and reduces the pores, and in turn improves the frost resistance durability of concrete. The service life prediction results obtained with Gray Model and Weibull Model are roughly similar, among which, Gray Model needs less sample volume, while Weibull Model presents more accurate prediction results.