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Soil–water characteristic curve (SWCC) and suction stress characteristic curve (SSCC), as the core of unsaturated soil mechanics, are important constitutive relationship curves for unsaturated soils, which can accurately describe the stress state in the soil. This paper examines the pore size distribution curves (PSD) of loess collected from Yan'an, China, by performing nuclear magnetic resonance (NMR) tests. In this paper, the Young–Laplace theory and the fractal model are combined with the PSD to establish the relationship between matric suction and volumetric water content. Finally, it establishes a mathematical model for predicting SWCC and SSCC. In addition, the evolution of SWCC and SSCC under different dry densities of compacted loess was studied based on the predictions. The study found that pore volumes with pore diameters smaller than the critical pore diameter could be used to predict the residual water content. Additionally, the water-holding capacity can be expressed in terms of the fractal dimension, which is controlled by the PSD. Based on the rapid characteristics of the NMR test, this paper makes a rapid prediction of SWCC and SSCC. It gives a new idea for the subsequent rapid testing of SWCC and SSCC. [ABSTRACT FROM AUTHOR]

To solve the problem where the prediction formula for vibration velocity by dynamic compaction cannot fully reflect the elevation amplification effect, the elevation amplification effect of vibration velocity by dynamic compaction was studied theoretically, and the factors that influence the elevation amplification effect of vibration velocity by dynamic compaction were systematically analyzed in this paper. The elevation amplification effect of a loess high slope under dynamic compaction is coformed by the refraction and reflection superposition effect of dynamic compaction vibration waves at the soil layer interface and the diffraction effect of dynamic compaction vibration waves. The propagation path of dynamic compaction vibration waves in soil was analyzed, and the elevation amplification effect was verified theoretically. The related physical quantities that affected the dynamic compaction vibration velocity of a loess high slope were analyzed based on the dimensional analysis method, and the calculation and improved calculation formulas that considered the elevation amplification effect of dynamic compaction vibration velocity were obtained. The multiple regression analysis of the calculation and improved calculation formula that considered the elevation amplification effect of the dynamic compaction vibration velocity was carried out using MATLAB with engineering examples. The results show that the relative error of the two formulas is small when the elevation difference is small; when the elevation difference is large, the calculation accuracy of the improved calculation formula that considered the elevation difference is higher, and it is more in line with the actual situation. Finally, according to the selected maximum allowable value of the slope particle velocity (e.g., 1.5, 2.0, and 2.5 cm/s), the allowable safe distance for dynamic compaction on a loess high slope is proposed area of northern Shaanxi Province, China. The results of this paper could provide a reliable basis for predicting vibration velocity by dynamic compaction in the Loess Plateau area of northern Shaanxi Province, China. They might have a reference value for dynamic compaction vibration control under similar terrain environments with large elevation differences and provide a safe guide for a dynamic compaction construction site in the Loess Plateau area of northern Shaanxi Province, China. [ABSTRACT FROM AUTHOR]

In view of the low accuracy and incompleteness of surface fissure extraction in mining areas, this paper takes the surface fissures in the visible light image of a mine in western China as an example, enhances the difference of spectral characteristics of the image by hue–saturation–intensity transformation, and then gets the rough extraction of ground fissures by combining the edge detection algorithm based on Sobel operator and Prewitt operator. Aiming at the discontinuity of ground fissures in remote sensing images due to the weak contrast with the environmental background, this paper uses the regional growth method based on pixel and object-oriented to realize the continuous expression of fracture areas. First, the growth area of ground fissure seed points is established, and the similarity judgment criterion based on the spectral characteristics and the real morphological characteristics of the fissure are proposed. Then, the pixels meeting the conditions are merged with the extracted objects to solve the problem that which is difficult to continuously extract ground fissure under the influence of "same object different spectrum" and vegetation coverage. The results of uniform sampling analysis show that the extraction integrity of fissures with width greater than 20 cm in 2.1 cm/pixel visible light image is 98.69%. The extraction integrity of fissures with width 10–20 cm is 86.54%. Part of fissures with width < 10 cm were also extracted, and the extraction integrity was 58.62%. The average extraction accuracy of fissures width fluctuates around 80%. [ABSTRACT FROM AUTHOR]

The upper reaches of the Yellow River in China, influenced by erosion of the Yellow River and tectonic activities, are prone to landslides. Therefore, it is necessary to investigate the existing landslide traces. Based on visual interpretation on high-resolution satellite images and terrain data, supplemented and validated by existing landslide records, this paper prepared the most complete and detailed landslide traces inventory in Jianzha County, Huangnan Tibetan Autonomous Prefecture, Qinghai Province, to date. The results indicate that within the study area of 1714 km², there are at least 713 landslide traces, ranging in scale from 3,556 m2 to 11.13 km², with a total area of 134.46 km². The total landslide area excluding the overlap area is 126.30 km². The overall landslide point density and area density in the study area are 0.42 km[sup -2] and 7.37% respectively. The maximum point density and maximum area density of landslide traces in the area are as high as 5.69 km-2 and 98.0% respectively. The landslides are primarily distributed in the relatively low-elevation northeastern part of Jianzha County, characterized mainly by large-scale loess landslides, with 14 landslides exceeding 1x10[sup 6] m². This inventory not only supplements the landslide trace data in the transition zone between the Qinghai-Tibet Plateau and the Loess Plateau, but also provides an important basis for subsequent landslide risk zoning, response to climate change, and landscape evolution. Additionally, it holds significant reference value for compiling landslide inventories in similar geological environments. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of clayey loess is strongly affected by the soil structure, but although anisotropy has been identified in loess by some, the anisotropy of small-strain behaviour is rarely reported. This paper presents an experimental study on the inherent and stress-induced small-strain shear stiffness anisotropy of a clayey loess from China. Both undisturbed and reconstituted specimens were tested with bender elements under isotropic compression and shearing conditions. Under an isotropic stress state, an inherent anisotropy was found for undisturbed specimens, while the reconstituted specimens prepared by moist tamping behaved isotropically. During shearing, the ratio of horizontal to vertical shear moduli of the undisturbed specimens decreased due to both an increase of stress anisotropy and the destruction of the intact structure. In contrast, the stiffness ratio of the reconstituted specimens only decreased due to stress anisotropy and it became more anisotropic at the critical state. This study reveals the influence of intact structure and inherent anisotropy on the behaviour of loess soils, which cannot be reproduced by compaction, thus highlighting the importance of characterising the undisturbed loess. [ABSTRACT FROM AUTHOR]

The problems of gully and soil erosion caused by large-scale urban construction and agricultural development in China have become more and more serious in recent years. In an effort to solve this problem, a series of gully stabilization and highland protection projects have been carried out on the Loess Plateau, and this has resulted in a large number of high-loess-filled-slopes (HLFSs). Although these filled slopes uses several different mitigation measures, the HLFSs have been eroded and destroyed under the action of water. In order to study the influence of different mitigation measures on the stability of HLFSs and their failure process, this paper uses a flume test of the effects of various mitigation measures on this failure process. The results show that: (1) the failure processes of slopes with different mitigation measures are obviously different. Slope deformation u with a declining gradient mitigation mainly occurs on the surface of the slope body, and although slope erosion is quite serious, the slope does not fail as a whole. Slopes with a stepwise drainage channel mitigation show little erosion, but material can easily slide along the horizontal drainage channels. (2) The slope deformation process is correlated with changes in pore-water pressure. When local instability occurs, there is always a pre-process of continuously rising pore-water pressure. When a failure occurs, the pore-water pressure of the soil at each position of the slope body suddenly fluctuates under instantaneous excitation. (3) The response of soil pore pressure and the development characteristics of tension cracks affect the deformation of the slopes, which is also the cause of the differences slope instability caused by different mitigation measures. These research results provide reference for the protection of HLFS engineering projects from heavy rains. [ABSTRACT FROM AUTHOR]

Compacted loess soil is used as a geo-material in many engineering projects, such as building foundations and highway embankments. Water infiltration characteristics and post settlement of the compacted loess in large construction projects of Northwest China have received increasing attention from researchers and investors. These behaviors are closely related to the soil water characteristics. This study aims to investigate the soil water characteristic curves (SWCCs) of compacted loess soil with different dry densities and to reveal the responsible micro-mechanisms for soil water characteristics. Loess soil collected from the new district of Yan'an City, China, is prepared into five dry density groups. The SWCC of each group in the suction range of 0–105 kPa is measured using the filter paper method (FPM). Two-dimensional (2D) images and the pore size distribution (PSD) curves of the specimens are tested by scanning electron microscopy (SEM) and the mercury pressure method (MIP), respectively. The results of this study highlight that the compaction behavior mainly influences the pores with a radius (r) in the range of 1–10 μm, and has no influence on the pores of r < 0.5 μm. The particle shapes among the five dry densities groups are similar. The characteristics of the PSD curves of the compacted loess soil correspond well to the SWCCs. The suction of the SWCCs increases with increasing dry density in the lower suction range of 0–100 kPa. In contrast, suction among the five dry density groups is almost identical in the suction range exceeding 100 kPa. The results of the study are helpful to understand the SWCC and microstructure characteristics of compacted loess with different dry densities. [ABSTRACT FROM AUTHOR]

At present, the international evaluation method of loess collapsibility only evaluates loess once collapses, but some scholars have found that loess is characterized with the phenomenon of repeated collapsibility under certain conditions. To explore the characteristics of repeated collapsibility of loess and to find a simple and feasible method for evaluating repeated collapsibility of loess, this paper selects soil samples with different water content for repeated compression tests. Loess is a typical structural soil, and its structure is significantly weakened by water and pressure. This paper combines three main parameters influencing the structure of loess to define a comprehensive physical index and explores the relationship between the comprehensive physical index and the structural yield strength of loess under repeated collapsibility. Using the structural yield strength of loess to normalize the compression curve during repeated collapse, a method for evaluating repeated collapsing of loess has been proposed. This method combines the compression index of loess with the basic physical parameters of loess, which is more suitable for evaluating the repeated collapsibility of loess. By comparing the calculation results with the measured results, it was determined that this method has high accuracy. This method was used to calculate the coefficient of collapsibility of Guyuan loess, and the results show that loess with a moisture content of < 17% can collapse twice. [ABSTRACT FROM AUTHOR]

This study addresses the challenge of deformation and failure on loess slopes, predominantly triggered by rainfall, by evaluating the efficacy of various slope protective measures. Recognizing the escalating preference for ecological protection techniques, this paper focuses on identifying optimal strategies that align with local rainfall patterns. A comprehensive analysis of loess slopes under diverse rainfall conditions was conducted, encompassing scenarios with prime soil, stabilized soil, and no protection. Utilizing the finite element software ABAQUS, a sophisticated rainfall infiltration slope model was developed and validated against experimental data. The investigation reveals that under low rainfall intensities, the choice of protective material—whether stabilized or prime soil—exerts limited influence on slope pore pressure. In contrast, at higher rainfall intensities, the impact of these protective materials on slope stability becomes significantly more pronounced. [ABSTRACT FROM AUTHOR]

The loess hilly region is a typical ecologically fragile and sensitive area. It is of great significance when measuring the balance between supply and demand of ecosystem services and clarify the relationship between supply and demand of ecosystem services for scientific ecological restoration zoning and realizing regional ecological security and social and economic sustainable development. We take Yuzhong County in the loess hilly region of Longzhong, China as an example; by constructing the matching and coordinating relationship between ecosystem service supply and demand and following the idea of "problem diagnosis—strategic orientation—key optimization", this paper delimits the ecological restoration zones and proposes corresponding governance strategies. The results show that: (1) The supply and demand of ecosystem services were mainly at a low and medium level, with significant spatial heterogeneity. Overall, the spatial pattern of ecosystem services showed high supply and low demand in the southwest mountainous areas and showed low supply and high demand in the urban gully areas of Yuzhong. (2) There were four types of spatial matching of ecosystem service supply and demand: HH type, LH type, LL type, and HL type. The local spatial autocorrelation of supply and demand was dominated by high-low or low-high spatial misadjustment. The average degree of coordination between supply and demand of ecosystem services was 0.629, indicating that supply and demand were basically coordinated. (3) The ecological restoration zones in Yuzhong County can be divided into six categories: the ecological core protection area, ecological potential restoration area, key ecological restoration area, soil and water conservation restoration area, ecological agriculture development area, and ecological innovation promotion area. The results of this study can provide ideas for the refined management and targeted restoration practice of regional ecosystem services. It provides a strong guarantee for ecosystem management and decision-making in the loess hilly region. [ABSTRACT FROM AUTHOR]

The deterioration of loess collapsibility under drying–wetting cycles is one of the serious threats to the artificial loess slopes and foundations in China, especially when soluble salt is involved. In this paper, a series of collapsibility tests were used to study the collapsibility deterioration of compacted loess with sodium sulfate under drying–wetting cycles, and the scanning electron microscope (SEM) tests were carried out to investigate the variation in microstructural properties. The results show gradual increase in the collapsibility of the loess samples with the increasing drying–wetting cycles and salt content. The collapsibility coefficient increases and gradually tends to stabilize with the progress of drying–wetting cycles, while changes linearly or exponentially with the salt content. The coupling effect of drying–wetting and salt erosion makes the loess skeleton looser and weaker in structure, providing more pore space for the deterioration of collapsibility, and when the salt content is greater than 0.5%, the deterioration ratio due to salt erosion is higher than that of drying–wetting. By fitting the collapsibility deterioration data with the hyperbolic function, the effect of drying–wetting cycles and salt content on the maximum and development speed of deterioration rate are quantitatively analyzed, and then, an interpolation equation of collapsibility deterioration considering both the influencing factors is established, which can well evaluate the collapsibility deterioration of compacted loess. [ABSTRACT FROM AUTHOR]

Due to their practicability, simple and data-driven empirical models have been extensively developed and applied in practical engineering to predict the run-out distance of landslides. However, the definition of the most appropriate empirical model for specific landslide data is rarely discussed. Moreover, the empirical model is subjected to the high variability of landslide data, which should be quantified into the model to provide more reliable predictions. As such, we propose in this paper, a simple, practical, and probabilistic run-out distance prediction method based on an empirical model and Bayesian method. This method was implemented with a regional landslide inventory compiled from 34 loess landslides in Heifangtai Terrace, Gansu Province, China. In this method, we performed a Bayesian model selection to determine the most appropriate empirical model for the compiled database among the possible candidate models adapted from previous literature. Considering the high variability of data, unknown parameters of the empirical model are regarded as random variables, and their posterior distributions are obtained by Bayesian updating with the compiled database. Then, we developed the probabilistic run-out prediction model to evaluate the run-out distance exceedance probability of landslides based on the most appropriate model and its associated posterior random variable information. We utilized data from two recent landslides that occurred in Heifangtai Terrace to validate the performance of the proposed model. In addition, we produced a run-out distance exceedance probability curve using the proposed method for a potential landslide in Heifangtai Terrace, in which the sliding volume interval is estimated using the sloping local base level (SLBL) method. In general, this study presents a practical method for landslide run-out distance analyses within a probabilistic framework, aiming to provide support for risk-based decisions. [ABSTRACT FROM AUTHOR]

This is a paper about the speed and intensity with which new and intensive human land use in a semi-arid environment can bring about large-scale environmental change. In particular, this paper pinpoints how and why it was that the Yellow River shifted from a long-term condition of relative stability to a later state of frequent floods and course changes in the eleventh century. It is possible to trace the environmental history of this dramatic and sudden change of state with precision and confidence. Historical sources that record the dates and characteristics of flood events downstream align well with those that note the locations and dates of human activity upstream. More important, each aligns well not only with one another, but also with information from environmental science: sediment cores that preserve soil and pollen evidence for the timing and processes of systematic change. [ABSTRACT FROM AUTHOR]

Coupled effects of railway vibration, rainfall, and drying-wetting cycles contribute to new types of loess disasters such as the collapse and vibration-induced settlement of the railway subgrade, loess mass disintegration, and slope sliding, during the large-scale construction and operation of high-speed or heavy-haul railways in China. This has significant consequences for railways that require millimetre-level deformation control, seriously threatening railway operation and people's lives. Therefore, for the first time, "five vibration-induced effects" on loess subjected to vibration, water immersion, and dry-wetting cycles are discussed including the vibration-induced acceleration of cracking, infiltration, disintegration, sliding, and subsidence. In this paper, the vibration-induced acceleration of infiltration is discussed mainly. The response of loess to locomotive vibration along railways was determined using field sampling and data processing. The dominant frequency of locomotive vibration are 18–22 Hz and the maximum amplitude is 0.4 mm. Tests regarding the vibration-induced acceleration of the permeability were conducted on intact loess using a newly developed vibration permeability apparatus. The results reveal that the vibration accelerates the water permeability and increases the water saturation of loess. The permeability coefficient of saturated loess under vibration is ∼1.5–20 times of that without vibration, reaching a maximum at a vibration frequency of 20 Hz. Vibration-induced infiltration tests were carried out on a loess column and the vibration-induced acceleration of water infiltration, wetting front evolution, and air outflow were analysed. The vibration-induced acceleration of infiltration strongly depends on the dry density, vibration frequency, and vibration amplitude. This pioneering work explores the mechnism of loess disasters triggered by locomotive vibration, rainfall, and drying-wetting cycles. [ABSTRACT FROM AUTHOR]

The seismic effects on sloped terrain, which are of paramount importance for engineering design and earthquake risk mitigation, have always been a central focus of earthquake engineering research. In this study, generalized geometric models of loess ridges at varying heights were created, and a three-dimensional nonlinear numerical model was established using FLAC3D. Seismic ground motion time histories at different frequencies and actual earthquake ground motion records were input into the model to analyze the peak acceleration amplification effects experienced by the surface of loess ridges when subjected to SV waves. The study's outcomes reveal that seismic amplification on the slopes of loess ridges is characterized by non-linearity with respect to slope height. Instead, it exhibits rhythmic variations, with the rate of change in these rhythms increasing in correspondence with the frequency of seismic motion and the height of the slope. Under low-intensity seismic motion, a linear increase in acceleration amplification is observed at the ridge's crest concerning the height of the loess ridge. However, under high-intensity seismic motion, the relationship between amplification and slope height becomes less significant. Typically, the peak acceleration at the ridge's crest is reported to be 1.5 to 2.5 times that observed at the slope's base. The amplification effect at the ridge's crest is more pronounced in the low-frequency and high-frequency segments when compared to the mid-frequency range. Conversely, significant amplification is observed in the high-frequency range in the lower sections of the slope near the base. It is further noted that the amplification effect at the ridge's crest displays distinct behavior at different frequencies, characterized by narrow frequency bands of maximum amplification, with peak amplification factors exceeding 10 in some cases. These research findings have practical significance and provide valuable references for engineering construction and seismic risk mitigation planning in loess regions. [ABSTRACT FROM AUTHOR]

The widely distributed loess–mudstone strata structure in the Loess Plateau of China is one of the fundamental reasons for the susceptibility and group occurrence of seismic landslides in the area. This study took the loess landslides induced by the Haiyuan earthquake as a case study. Through extensive field investigations, the loess cover thickness, mudstone dip angle, slope height, and slope angle were chosen as the influencing factors. Together with mathematical statistics and geotechnical tests, two models, one of a loess–mudstone slope and the other of a pure loess slope, were constructed. Their seismic stabilities under different slope angles and slope heights were compared to analyze the influence of the underlying mudstone strata on the loess slope seismic stability. Meanwhile, a sensitivity analysis of these strata factors affecting the seismic stability of the loess–mudstone slope was carried out based on the orthogonal test. The results showed that ignoring the underlying mudstone strata would lead to smaller calculation results than the actual situation. The sensitivity influence of the factors on the loess–mudstone slope seismic stability comprised the slope angle, loess cover thickness, slope height, and mudstone dip angle from high to low. [ABSTRACT FROM AUTHOR]

The Loess Plateau is an ecologically fragile area in China; furthermore, loess landslides are typical forms of geological disasters, which severely limit the sustainable development of the local societies and the economy. Studying the automatic detection of landslides can facilitate disaster prevention and mitigation in the Loess Plateau, and help realize the climate action goal (SDG 13) of the United Nations Sustainable Development Goals (SDGs). This paper takes typical loess areas in China as the research object, and establishes a historical loess landslide sample database based on Google Earth (GEE) image data, with a total of 1451 loess landslides. The automatic detection of loess landslides is implemented by improving the You Only Look Once X (YOLOX) algorithm. The results show that the average accuracy of landslide detection in this method is 95.43%, and the accuracy rate is 96.32%, which effectively combines the earth's big data to realize the automatic detection of loess landslides. The research results provide technical support for the promotion of disaster prevention and mitigation in China's loess regions, the realization of sustainable development goals, and the improvement of natural disaster prevention–resistance–reduction systems. [ABSTRACT FROM AUTHOR]

With the development of transportation infrastructure construction in West China, more and more mountain tunnels covered by loess are encountered in the construction projects. The tunnel excavation and construction cannot ignore the problem of crossing the special stratum of soil-rock contact zone. Aiming at the technical problem of tunneling under the special stratum conditions of soil-rock contact zone covered with loess, this paper uses the finite difference software FLAC3D to simulate the three-dimensional modeling numerical calculation and analysis under up-down benching excavation and construction conditions, and analyzes the failure characteristics of surrounding rock in soil-rock contact zone from three aspects: shear displacement in soil-rock contact zone, plastic zone in soil-rock contact zone and primary lining internal force. [ABSTRACT FROM AUTHOR]

With the implementation of China's western development and "One Belt, One Road" initiative, there are more and more projects in the collapsibility loess area, and the collapsibility loess problem encountered in the construction is becoming more and more prominent. In this paper, the collapsibility loess of the south extension section of Xi'an Metro Line 2 is investigated, and its collapsibility characteristics are studied through a large-scale site immersion test. The test site was a 15 m diameter circular test pit, which took 35 days for water injection and 60 days for observation after water stopped. The test results showed that the maximum self-weight collapsibility of the soil layer in the test pit is 32 mm, and the deformation amount is 10.05 mm in Q3 and 9.55 mm in Q2. The maximum deformation amount of 32 mm is less than 70 mm in the shallow marker; it may be caused by the paleosol layer as a bridge to provide a support to the overlying soil layer. The shape of the sphere of influence after immersion resembles a trumpet, slightly protruding outwards from the paleosol. The scope of influence between the infiltrated and saturated zones gradually increases with depth, and the saturated zone is generally smaller than the infiltrated zone. The research results of this paper can provide technical support and reference for the construction of Xi'an Metro Line 2 and other related projects in the region. [ABSTRACT FROM AUTHOR]

It is difficult to obtain reliable shear strength parameters for the stability analysis and evaluation of high loess slopes. Hence, this paper determines slope elements and physical parameter of 79 slopes with heights of [40, 120] m based on the measured loess slopes in the Ganquan and Tonghuang subregions of northern Shaanxi Province, China. In the limit state of the loess slope (stability factor Fs is 1.0), a fitting equation for the slope height and width is established. Then, the model is developed by stability analysis software-SLOPE/W, and the comprehensive shear strength parameters corresponding to different slope heights of the high slope in the study area are obtained by inversion using the Morgenstern-Price method. The results show that when the height of the slope increases, the cohesion c increases in the soil, and the internal friction angle φ decreases. This change is consistent with the characteristics reflected in the composition and physical properties of the slopes, and the comprehensive strength parametric curves are very similar between the Ganquan subregion and the Tonghuang subregion. A landslide that occurred in Miaodian-zaitou of Jingyang County, Shaanxi Province, is selected to verify this inversion method, and the results show that the calculated shear strength parameters of the inversion are consistent with the measured value of the actual slope. [ABSTRACT FROM AUTHOR]

As the global climate warms, the frequency of soil slope failures induced by snowmelt is gradually increasing, especially loess landslide disasters in seasonally frozen areas. Landslide disasters in seasonally frozen areas pose a serious threat to human lives and engineering constructions and are gradually drawing greater public attention around the world. However, the mechanism that regulates deformation and failure processes, resulting in snowmelt-driven landslides, remains elusive. The Yili River Valley in Xinjiang, China, is an ideal location for exploring the mechanism of snowmelt-driven landslides. Based on detailed field surveys, remote sensing image identification, meteorological data analysis and loess characteristic tests, this paper takes a representative high-level loess landslide in north-west China as a case in order to explore its evolution history, movement process and resurrection mechanism. It was found that this loess slope had suffered two large-scale sliding failures and different degrees of inherited slope deformation had been found between the two slope failures. The 32 surface cracks identified have a total length of 3,505.10 m, and the total area of the landslide was found to be 135,462m2. The average thickness of the sliding body was about 30 m, and the volume was approximately 504,000 m3. The actual movement time lasted for 32 s with an average moving speed of about 15 m/s. Human grazing activities dominate the formation and development of slope surface cracks in the early stage. The strong water sensitivity of distinctive loess controls soil strength deterioration in the slip zone. Rapid snow removal and infiltration, driven by an abnormal temperature rise in Spring, is the most important triggering factor for slope deformation, evolution and failure. As regional grazing activities increase and global warming intensifies, the potential for resurrection landslides will increase. The results provide essential information for a comprehensive understanding of early warning systems and risk assessment for snowmelt-triggered landslides in cold areas. [ABSTRACT FROM AUTHOR]

Purpose: The differences in particle composition and consistency limits result in the challenge in comparing the freezing points of different types of loess. The clay activity that well links the clay content and the plasticity index suggests a response to the above challenge. The purpose of this study is to evaluate the relationship between freezing point and clay activity of loess in different areas of Loess Plateau of China. Materials and methods: The test loess was sampled from eight typical areas of the Loess Plateau of China, which could be classified as the lean clay (CL). The clay activity of loess was obtained based on the plasticity index and the clay fraction (< 5 μm). The freezing point and soil freezing characteristic curve (SFCC) of loess were measured by the 5TM transducer from METER Group, while the soil water characteristic curves (SWCC) were determined by the filter-paper method. Results: When the clay activity is below 0.948, the freezing point increases with higher clay activity; otherwise it rises slightly, which is in contrast to the change of matric suction. A proportional function was approximated between freezing point and matric suction. The SFCC decays more sharply at greater initial water content, compared to that at higher clay activity. The free water content increases slightly with higher clay activity while the weakly bound water content declines, resulting in an insignificant change in the freezable water content. Based on the normalization of SFCC, an exponential model incorporating the effect of clay activity was established and verified. The clay activity of loess decays as the calcium chloride content increases, which shows a good linear relationship with freezing point. Conclusions: The freezing point of loess shows high relevance to the clay activity. The clay activity–based freezing point predictive model well considers the differences in clay content and consistency limits of loess in different regions. [ABSTRACT FROM AUTHOR]

Coal fires refer to fires generated by the self-combustion of coal seams, which have a maximum temperature of 1000 °C. Such fires can significantly alter the properties of surrounding rock and soil. However, in Northern Shaanxi, China, coal resources are abundant, and the buried depth of coal seams is shallow; therefore, coal fires often occur. Because Northern Shaanxi is located in China's Loess Plateau, there is a large amount of loess accumulation on the surface. For this reason, it is imperative to study the effects of high temperatures on loess. In this paper, the loess samples are heat treated at different temperatures (200–1000 °C), and their surface redness (a*) and mass magnetic susceptibility (χ) are measured to simulate the high-temperature effects of coal fires on the loess in northern Shaanxi, and also study its chromaticity changes and abnormal magnetic properties. The results show that (1) the loess χ value is affected by the heat-treatment temperature; at 600 °C, the χ value decreases, increasing rapidly above after 850 °C. Further, the magnetic susceptibility changes significantly. (2) The thermal-induced transformation of ferromagnetic minerals and the buried depth of loess are the main reasons for these changes in magnetic susceptibility and red chroma of loess. [ABSTRACT FROM AUTHOR]

This paper studied the anti-seepage ability of the modified loess by using attapulgite, which is abundant in local areas. The possibility of using the modified loess as the sustainable compacted soil liner material in a solid waste landfill was also considered in this research. The materials were then evaluated using Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and an Impermeability Mechanism (IM). The experimental results showed that the permeability coefficient of the attapulgite-modified loess decreases significantly with increasing attapulgite content. However, it becomes less significant when the attapulgite level approaches 10%. Both cases can meet the landfill impermeability requirements, based on the attapulgite content remaining at 10%, adding 15% lime or 5% cement, respectively. The triaxial consolidation and drainage experiment was carried out to investigate the shear strength of the materials under three different working circumstances. The stress–strain curves of each specimen were produced, as were the cohesion and internal friction angle values. This research lays the groundwork for using attapulgite-modified loess as a landfill lining material. It establishes a solid platform for future studies on attapulgite adsorption and purifying performance in landfills. [ABSTRACT FROM AUTHOR]

To explore the microscopic mechanism underpinning the dynamic characteristics of saturated loess, dynamic triaxial tests were conducted on saturated loess in Xianyang City, China. The tests were performed under dynamic loads of different waveforms, confining pressures, frequencies and amplitudes. Under each dynamic load, the test included two states: one stopped after 12 loading cycles, and the other is to vibrate to the failure state. Furthermore, a scanning electron microscope test was carried out on the undisturbed samples and the sheared dynamic triaxial samples. In this paper, the dynamic elastic modulus of samples is used to represent the dynamic characteristics, and parameters such as the diameter, average abundance, average fractal dimension, and directional probability entropy of the structural units and pores are selected to describe the microstructural characteristics of samples. The results show that the dynamic elastic modulus of samples decreases with increasing number of loading cycles or axial strain and finally stabilises when different types of dynamic loads are applied. The types of dynamic loads exert a significant influence on the microstructural parameters of structural units and pores. [ABSTRACT FROM AUTHOR]

Frequent occurrence of landslides has seriously threatened the infrastructural projects in the Loess Plateau, China. At the beginning, with development of the landslide, several fissures were generated along the internal weak surface. Then, under the constant influence of rainfall and irrigation, the fissures were expanded and connected, which formed a consecutive sliding surface, consequently leading to the occurrence of the landslide. Therefore, the key to treat the landslide is to prevent the expansion and connection of fissures in the potential slip zone inside the slope. In this paper, an old landslide, which occurred at an early stage of the construction of the Lvliang Airport, was selected as a case study. A new type of grouting material was used to fill the fissures and reinforce the loess in the slip zone, so as to study the effect of material content on the slope stability. With current methods, loess specimens were taken from the slip zone inside the Lvliang Airport slope. Based on the GDS triaxial test system, a series of laboratory tests were performed on the undisturbed loess and the remolded which contained the stabilizer, including triaxial shear tests at constant matric suctions and wetting tests at constant deviator stresses. Moreover, the dichotomy in mathematics was chosen to find the threshold of the material content. The test results showed that the cohesion and the internal friction angle of the loess obviously increased after grouting. The failure behaviour of the loess along the wetting path was dependent on the material ratio and the stress level. Meanwhile, the critical state line of the slope, grouted with materials of different ratios, was compared by fitting the regression equation. It was found that the threshold value of the stabilizer content was between 15% and 20%, which was the most suitable ratio for improving slope stability with relatively lower cost. [ABSTRACT FROM AUTHOR]

The moisture and the temperature variation of shallow loess during the freeze-thaw process have tremendous influences on the freeze-thaw disease and agricultural development. The present paper, based on the field test of the temperature and water content of the shallow loess in the seasonal frozen region, probes into the variation of the temperature and moisture fields of shallow loess in the freeze-thaw period. Field test shows that the daily variation of surface temperature reaches the maximum with the peak temperature appearing around 14:00, and the time when the peak temperature appears gradually postpones as the depth increases. Moreover, the daily variation of soil temperature decreases with the increase of temperature, and the variation can be ignored given the depth of more than 30 cm. In addition, there is an obvious variation of moisture content in shallow soil under the action of freeze-thaw cycles. In this regard, the coupled calculation model is proposed in this paper to simulate the dynamic variation of temperature and moisture in shallow soil in Bin County located in Western China under natural conditions, compare the calculation value with the measurement value, and further verify the rationality of the numerical calculation method and parameter selection. Furthermore, the variation law of the maximum frozen depth with the air temperature is obtained through the simulation of extreme cold climate conditions. [ABSTRACT FROM AUTHOR]

Loess landslides are one of the geological hazards prevalent in mountainous areas of Loess Plateau, seriously threatening people's lives and property safety. Accurate identification of landslides is a prerequisite for reducing the risk of landslide hazards. Traditional landslide interpretation methods often have the disadvantage of being laborious and difficult to use on a large scale compared with the recently developed deep learning-based landslide detection methods. In this study, we propose an improved deep learning model, landslide detection- you only look once (LD-YOLO), based on the existing you only look once (YOLO) model for the intelligent identification of old and new landslides in loess areas. Specifically, remote sensing images of landslides in Baoji City, Shaanxi Province, China are acquired from the Google Earth Engine platform. The landslide images of Baoji City (excluding Qianyang County) are used to establish a loess landslide dataset for training the model. The landslide data of Qianyang County is used to verify the detection performance of the model. The focal and efficient IoU (Focal-EIoU) loss function and efficient channel attention (ECA) mechanism are incorporated into the 7th version of YOLO (YOLOv7) model to construct the LD-YOLO model, which makes it more suitable for the landslide detection task. The experiments yielded an improved LD-YOLO model with average precision of 92.05%, precision of 92.31%, recall of 90.28%, and F1-score of 91.28% for loess landslide detection. The landslides in Qianyang County were divided into two test sets, new landslides and old landslides, which were used to test the detection performance of LD-YOLO for both types of landslides. The results show that LD-YOLO detects old landslides with a detection precision of 82.75% and a recall of 80%. When detecting new landslides, the detection precision is 94.29% and the recall is 91.67%. It indicates that our proposed LD-YOLO model has strong detection performance for both new and old landslides in loess areas. Through a proposed solution that can realize the accurate detection of landslides in loess areas, this paper provides a valuable reference for the application of deep learning methods in landslide identification. [ABSTRACT FROM AUTHOR]

Due to unique landform and lithological features of the loess gully area, the geological disasters caused by coal mining have become more complex. Moreover, the advancing direction of the working face has an important influence on the deformation of the slope on both sides of the gully. In this paper, combined with the specific conditions of a coal mine working face in western China, we use the method of particle flow numerical simulation and theoretical analysis to examine and observe the deformation, as well as characteristics of failures in the loess gully area under different mining directions of the working face. The deformation process of the gully area can be obtained by combining the numerical simulation results. According to different mining directions of the working face, the failure mode of mining in the loess gully area was divided into the back slope and along slope advancing failure modes. Through empirical evaluation, our investigation demonstrates that the bottom of the gully was damaged seriously by both along slope mining and back slope mining. Albeit the influence of coal seam excavation on the slope surface was relatively small; however, it is greater on the flat ground of the upper slope. Under the same mining conditions, the advancing direction of the working face affected the horizontal movement of the loess gully area but had less effect on the subsidence. Furthermore, we observed that the failure mode of the mining slope is highly correlated with the mining direction and relative position of the working face. The results obtained from this research can provide useful information for deformation and failure prediction, working face mining method, and geological disaster assessment in the loess gully area. [ABSTRACT FROM AUTHOR]

An accurate understanding of the relationship between reservoir construction and the dynamic change of groundwater level in downstream areas is of great significance for rational development and utilization of water resources. At present, the research on the interaction between surface water (SW) and groundwater (GW) mainly focuses on the interaction between river and GW. There are few studies on the impact of the reservoir construction on GW level in downstream loess irrigation area. Rainfall, evaporation and climate temperature have a great impact on W level, but the impact of reservoir construction on the GW level should not be ignored in the utilization of water resources. In this paper, a GW flow model under a natural boundary was established by numerical simulation. Taking Heihe Jinpen Reservoir in Heihe River watershed as the research object, the influence of the construction of a mountain reservoir on the dynamic change of GW level in the downstream loess region is studied. By comparing the GW level under the natural state without reservoir construction and the measured GW level after the reservoir was built, the variation of the GW depth in the loess area of the lower reaches in the Heihe River watershed is obtained. The results show that simulation accuracy of the interaction between SW and GW was reasonable; after the Heihe Jinpen Reservoir construction, the mean GW level decrease was about 6.05 m in the downstream loess irrigation area in Guanzhong Basin. It provides a method for the simulation and prediction of SW–GW conversion laws. This study is also of great significance to explore the change law of the water cycle and improve the utilization rate of water resources. [ABSTRACT FROM AUTHOR]

Soil erosion is a major environmental problem of global concern. In the Loess Plateau region of China, erosion of loess slopes is one of the major modes of soil erosion, causing serious erosional problems. Most current studies of loess slope erosion use qualitative analyses from field investigations, while quantitative analyses from experimental physical simulations are relatively rare. This paper takes slope erosion, which is the most typical mode of loess erosion, as the starting point and investigates the hydraulic erosion process for different initial states using small-scale physical simulations. The slope erosion process can be generalised into two stages: rapid erosion, and slow and uniform erosion. Results of the physical simulations suggested that the initial dry density is negatively correlated with the erosion rate, but the initial water content is positively correlated with the erosion rate. The results of the study are not only of practical significance for the prevention and control of soil erosion on loess slopes, but also of theoretical significance, as they reveal the development of slope gully erosion. [ABSTRACT FROM AUTHOR]

The effect of lateral deformation on subgrade settlement is often ignored. This paper discusses this effect under different constraint conditions. Compression tests of typical Q2 remoulded loess from Shaanxi Province, China, were conducted under different confining pressures using a self-developed three-dimensional loading test device. The vertical and lateral deformation characteristics of loess samples were analysed, and a model of lateral strain in subgrade soil was derived. Then, a model of total subgrade settlement with consideration of lateral deformation was established based on the equal volume concept. The stratified summation calculation formula was also revised, and correction coefficients under different constraints are given. The results show that the accuracy of the revised method is positively correlated with the number of lateral constraints. The correction coefficient can reflect the influence of different subgrade constraints. Importantly, the modified model was verified by field measurements and found to be more accurate than the stratified summation method. These results help to understand the influence of lateral deformation on total settlement and the mechanism of subgrade settlement. [ABSTRACT FROM AUTHOR]

Due to the huge losses caused by landslides, landslide deformation monitoring has become essential. The change of the tilting angle of the slope surface can reflect the instability process of the landslide. However, there are few studies on the relationship between the instability process of landslides and the tilting angle of the slope surface on the time scale. Therefore, there are even fewer cases in using the inclination angle of the landslide as an early warning method in practice. On August 24, 2018, a wireless tilt sensor network was deployed in the Heifangtai area of Gansu Province in China, to monitor the inclination state of loess landslides to study the relationship between the tilting angle of the slope surface and the landslide instability process. At 4 o'clock on October 5, 2019, the wireless tilt sensor network mentioned above detected a new loess fall landslide. Through the analysis of the monitoring data from the tilting sensor nodes named T3 and T4, we found that the tilting angle of the landslide surface in the pre-sliding stage has significant change compared with the stable stage, which directly verifies that the inclination data can be used for landslide warning. At the same time, we inputted the monitored inclination data into the inclination warning model proposed by Xie et al. (Landslides 17:301–312, 2020) for verification and found that the trend of inclination changes matches the model well. However, the forecast time error is large. Therefore, this paper optimizes the inclination early warning model proposed by Xie. Using the optimized early warning model, the predicted landslide occurrence time based on the data of the T3 node was 0.517 days, which was about 8 h later than the actual landslide that occurred on October 4, 2019, which is an improvement of forecasting. This case serves as an on-site direct evidence to further verify the feasibility of using the landslide body inclination state as a landslide monitoring and early warning parameter which can be promoted and used in practice. [ABSTRACT FROM AUTHOR]

• This paper provides a new idea for the genesis and evolution of loess tunnels in the Loess Plateau. • There are significant differences in the loess tunnel development density in the different topographic and micro-topographic units. • Spatial statistical modelling was employed to justify and predict the observed spatial distribution tendency of the loess tunnels. • The loess tunnel evolution process can be divided into five stages: the incubation stage, formation stage, development stage, failure stage, and withered stage. Loess tunnels are very common in the Loess Plateau, and they pose unique geological threats. Loess tunnels are often difficult to detect and control due to their concealment and sudden appearance. Thus far, research on the genesis and evolution of loess tunnels remains scarce. In this paper, the genesis and evolution mechanism of the loess tunnels in the Loess Plateau is studied in depth, and the location, shape, and size information are obtained via field investigations. The potential correlations between the loess sediment, the basic physical properties (depth, water content, particle size composition, collapsibility coefficient, and self-weight collapsibility coefficient), and the tunnel density are inferred based on the Pearson's correlation coefficients and tests on the physical and mechanical properties of the loess sediments. In addition, spatial statistical modelling is employed to justify and predict the observed spatial distribution of the loess tunnels assuming Gaussian Markov random fields. The formation of loess tunnels is due to a combination of factors, including the formation thickness, soil properties, joints and fissures, topography, hydrogeology, and climatic conditions. The thickness of the loess, loess sediment properties, and their spatial relationship jointly determine the material basis of the formation of the loess tunnels. The loess tunnels at different depths have different main controlling factors that are hierarchical by depth. The evolution process of loess tunnels can be divided into five stages: the incubation stage, formation stage, development stage, failure stage, and withered stage. The characteristics of each stage are discussed in detail. Our work provides novel insights into subsurface erosion from the aspect of soil tunnels. It improves our understanding of hill slope geomorphological evolution and also provides effective techniques for tunnel erosion control. [ABSTRACT FROM AUTHOR]

Loess presents very unique collapsible behaviour due to its special under-compactness, weak cementation and porousness. Many environmental issues and geological hazards including subgrade subsidences, slope collapses or failures, building cracking and so on are directly caused by the collapsible deformation of loess. Such collapsible behaviour may also severe accidents due to sinkholes, underground caves or loess gullies. Moreover, with the increasing demand of construction and development in the loess areas, an in-depth research towards effective evaluation of loess collapsibility is urged. Currently no studies have made attempts to explore a rather complete and representative area of Loess Plateau. This paper thus provides a novel approach on spatial modelling over Jin-Shan Loess Plateau as an extension to experimental studies. The in-lab experiment results have shown that shown that the porosity ratio and collapsibility follow a Gaussian distribution and a Gamma distribution respectively for both sampling areas: Yan'an and Lv Liang. This establishes the prior intuition towards spatial modelling which provides insights of potential influential factors on loess collapsibility and further sets a potential direction of the loess studies by considering an extra dimension of spatial correlation. Such modelling allows robust predictions taken into account of longitudinal information as well as structural parameters and basic physical properties. Water contents, dry densities, pressure levels and elevations of samples are determined to be statistically significant factors which affect the loess collapsibility. All regions in Lv Liang area are at risk of high collapsibility with average around 0.03, out of which roughly a third of them are predicted to be at high risk. Clear spatial patterns of higher expected collapsibility in the southwest comparing to the northeast are shown adjusting for influential covariates. On reference guidelines for potential policy makings, county-level regions with the highest expected loess collapsibility are also identified. [ABSTRACT FROM AUTHOR]

Loess slope broadly distributes in Northwest China, making the slope of the area developed. And with the development number of construction projects still on the rise, this area is a high-intensity region with multiple earthquakes, resulting in landslide under earthquakes which is a very serious problem. However, the study on the loess slope dynamic response yet rarely involved the exploration of the influence of slope shapes, which leaves a hidden danger to the safety of local engineering. In this paper, a typical ladder-type loess slope in engineering is selected as a research object, and a numerical simulation model is established with FLAC3D program. The dynamic response of the loess slope with different shapes is studied deeply and systematically. Found a series phenomenon of earthquake response of loess slope with stepped slope series, the width of the platform and the slope ratio change under earthquakes. Meanwhile, the law of slope parameters such as slope series, platform width, and slope ratio on dynamic response of loess slope is revealed. The results provide theoretical support and scientific basis for the construction of the relevant projects in the area, which has important reference value to the safety of the engineering and the development of economic society. [ABSTRACT FROM AUTHOR]

This paper describes an assemblage of diverse floodplain facies of reworked loess (facies b, c) in a Middle Pleistocene monsoonal setting of the Hanzhong Basin, central China. The vertical and lateral sedimentary sequences show changing energy conditions. Apart from the highest energy in the channel facies (facies a), a relatively high energy floodplain environment (facies b) prevailed in waterlogged conditions, with small, laterally migrating (sub)channels. Facies b generally interfingers with aggrading horizontal sheets of overbank deposits in alluvial pools and swamps in a floodplain with much lower energy (facies c), in which phases of stability (soil formation) occasionally interrupted overbank deposition. Reworked loess forms the main part of the floodplain deposits. The paleosols are considered to have been formed under low hydrodynamic conditions in an interglacial environment. These interglacial conditions follow the commonly assumed glacial conditions of channel facies a. The sedimentary successions in the floodplain show a recurrent composition and cyclicity between wet and dry floodplain sedimentation terminated by stability with soil formation. The cyclic rhythm of stacked high- and low-energy floodplain sediments is attributed to varied intensity of different hydrodynamic flooding events that may have been due to changing monsoonal rainfall or simple intrinsic fluvial behavior. [ABSTRACT FROM AUTHOR]

The Loess Plateau accounts more than 6% of China's land area and 45% of Shaanxi Province. The land-creation project could double the city's current area. However, the behavior of loess, and in particular inadequate compacted loess, can have significant implications on the safe and reliable operation of man-made infrastructure. The mechanical behavior and collapsibility of intact, in situ compacted and remolded loess in lab, which are widely recognized as fundamentally different materials, were associated with the microstructure. There is limited understanding of micro–macro-relationships in the three fine-grained loess. This study focuses on the microstructural changes and micro–macro-relationships of an intact, compacted and remolded loess from complex land-creation project. A comprehensive microstructural comparisons about PSDs, micrographs and quantitative evaluation for intact and remolded loess from an 80-m-high section of the sedimentary strata, and compacted loess from a highly filled exploratory well are presented and discussed in this paper. The results show that both the intact and compacted loess exhibit trimodal characteristics in their PSDs, while there are bimodal/unimodal characteristics of the PSD for the remolded loess. The compressibility and the specific surface area of the remolded loess are far less than those of the intact or compacted loess. This is further evidence the remolded loess is not suitable to study the collapsibility and compressibility instead of intact loess. However, compared with the intact loess, the compacted loess shows the same pore and particle flocculation structure characteristics for samples at higher density (> 1710 kg/m3 + 10 kg/m3). Under high-energy impact load, particles perform the breakdown, from round, coarse and disordered particles gradually to flaky, fine and ordered particles, which are different from traditional research results. The threshold value of dry density 1710 kg/m3 + 10 kg/m3 can be defined the boundary and micro–macro-relationships among intact, compacted and remolded loess. The results are of great importance to understand the microstructure characteristics and improve the engineering construction safety in loess areas. [ABSTRACT FROM AUTHOR]

The Loess Plateau can be considered as a landslide-prone area in northwest China. The genera consensus about the interaction between landslide deposit and terrace sediments is not well studied; this paper summarised 40 loess landslides in the South Jingyang Platform, Shaanxi Province, China to help understand of this issue. Four of the loess landslides with high mobility have been analysed in detail. Three trenches T1, T2 and T3 dug after the loess landslides LD37, LD11 and LD38 highlighted the landslide-induced changes in geomorphology and internal geometry of geology, respectively. Furthermore, observation of upwards seepage flow on the profile of trench T3 is believed to be the trigger of the high speed, and long runout flowslides in the study area. A newly developed sandbox apparatus is used to reproduce the landslide kinematics due to a mass travelling over an inclined plane. The sandbox experiments show that the sediments are sheared and pushed upwards after the collision with the deposits. The deposits are then wrapped in a space between sediments, which tends to form the 'sandwich' structure. The distal sediments are thrust when the loess deposits' kinetic energy consistently dissipates, developing the accumulated folded strata. These results reveal the deposits' interactions with the sediments in the study area and provide key guideposts regarding prevention and mitigation of loess landslide hazards. [ABSTRACT FROM AUTHOR]

Loess landslides have complicated deformation mechanisms. Accurately describing the internal failure deformation of loess landslides and establishing a theoretical method of landslide instability evaluation for the prevention of subsequent landslides have become important topics in western development project construction in China. This paper presents a case study of the Zhonglou Mountain landslide in Shaanxi Province, China. Based on field investigation results, a two-dimensional stability analysis model was constructed using the finite element method. Taking the deformation characteristics of the landslide as the research basis, the distribution laws of the displacement, stress, and shear strain of this landslide were identified with the strength reduction finite element numerical simulation method. Additionally, the safety factor was evaluated under normal and storm conditions. The numerical simulation results show that the horizontal tensile stress of the landslide was mainly distributed in the middle and upper parts of the landslide under normal conditions, while the vertical tensile stress was distributed near the sliding surface. Under heavy rainfall, the sliding force increased, and the anti-sliding force and anti-sliding section decreased; the location of the maximum shear strain shifted down from the middle and upper parts of the landslide body to the area with a shear crack, and the plastic shear strain area expanded along nearly the entire the sliding surface, leading to the occurrence of a landslide. Thus, the use of anti-slide piles to stabilize the landslide was proposed and tested. Monitoring points were arranged along the sliding surface to evaluate the displacement, stress, and strain responses. The on-site observation results agreed with the modeling results. The use of anti-slide piles was demonstrated to be an effective stabilization method for the Zhonglou Mountain landslide. [ABSTRACT FROM AUTHOR]

Landslide disasters are associated with severe losses on the Loess Plateau of China. Although early warning systems and susceptibility mapping have mitigated this issue to some extent, most methods are qualitative or semi-quantitative in the site-specific range. In this paper, a quantitative spatial distribution model is presented for site-specific loess landslide hazard assessment. Coupled with multi-temporal remote sensing images and high-precision UAV cloud point data, a total of 98 loess landslides that have occurred since 2004 on the Heifangtai terrace were collected to establish a landslide volume-date and retreating distance database. Eleven loess landslides are selected to construct a numerical model for parameter back analysis, and the accuracy of the simulation results is quantitatively evaluated by the centroid distance and overlapping area. Different volumes and receding distance rates of landslides are fitted to determine the relationship between cracks and potential volume, and different volumes and parameters are combined to simulate the spatial distribution of potential loess landslides. The results of this study reveal that landslide volumes mainly range between 1 × 103 and 5 × 105 m3, and the historical occurrence probability reaches 0.551. The optimal parameters are estimated by the maximum likelihood method to obtain a uniform distribution parameter value probability model, and the results show that the error of the estimated length within a range of 0.05 from the optimal parameter does not exceed 15%. In the selected slope slide case, farmland near the toe of the slope primarily includes exposed hazards with probabilities greater than 0.7. This work provides a useful reference for local disaster reduction and a theoretical methodology for hazard assessments. [ABSTRACT FROM AUTHOR]

Tunnels are commonly constructed in loess with a high water content or saturation degree, which can lead to large ground deformation, structural cracking, and even tunnel collapse during construction, in addition to tunnel leaks, sidewall settlement, and frost damage. A complete understanding of the distribution, source, and effects of groundwater in loess is therefore of critical importance, particularly to comprehensively consider loess landforms and material properties and tunnel design and construction practices. This paper presents a review and analysis of previous studies and 27 typical loess tunnels in China, which indicates three different types of water-rich loess surrounding rocks: natural water-rich loess (type I); excavation disturbance-induced water-rich loess (type II); and surface rainfall infiltration water-rich loess (type III). The formation mechanism, seepage field characteristics, and consequent stress and deformation characteristics of the surrounding rock are explained in detail. Key problems, strategies, solutions, and countermeasures are proposed as a helpful reference for theoretical research, design, construction, and maintenance of tunnel engineering in loess. [ABSTRACT FROM AUTHOR]

Geological materials have randomness in nature. Statistical analysis can help revealing the variation pattern of the material parameters and the reliability of the slope. In this paper, the probability distribution and variability of shear strength parameters of typical Q2 and Q3 loess in Northwest China were statistically analysed using the collected geological survey data in Yan'an, Shaanxi Province. Resulting probability properties were applied to the reliability analysis for the natural and fill slope in loess area using the Monte Carlo Method. Finally, an optimization analysis was carried out for the fill slope in the background engineering project. Research results show that normal distribution and lognormal distribution can be used to describe the statistical properties of c and φ of Q2 and Q3 loess. Variance of c is large while the variability of φ is relatively small. The influence of the variability of φ on the reliability index of loess natural slope is generally larger than that of c. On the contrary, influence of the variability of c on the reliability index of the fill slope is generally greater than that of φ, which is related to the structural and uniformity of the soil. Finally, relation between slope height and minimum gradient coefficient is linear when the failure probability of fill slope is less than 10%. Results in this study can be used as a reference for the slope design and construction for the cut and fill engineering in loess area. [ABSTRACT FROM AUTHOR]

This paper presents the results of relationship between structure and shear behavior of natural loess collected from Northwest China. The shear performance was conducted by triaxial tests. Scanning electron microscopy (SEM) in conjunction with MATLAB were used to interpret the microstructure characteristics of soil samples before and after triaxial tests, and mercury intrusion porosimetry (MIP) was performed on investigation of pore size distributions. Based on the MIP results, the pore distribution of natural loess at initial state can be divided into micropore (< 0.03 μm), fine pore (0.03–5 μm), medium pore (5–11 μm) and macropore (> 11 μm), respectively. The shear behavior during triaxial tests shows that, soil samples exhibit obvious homogenous deformation and yielding hysteresis with the increase of confining pressure, which is well agreement with the microstructure evolution characteristics investigated by means of SEM and MIP. It is found that strength loss of loess soils can be mainly attributed to changes in particle arrangement, breaking up and corresponding pore size variation. Quantitative and qualitative statistics analysis of soil particles and pore types shows that there is a negative relationship between confining pressure and parameters characterizing particle morphology, as well as between pore area and deviating stress. Although the structure of loess differs from region to region, the relationship between structural parameters and confining pressure or deviator stress can be used to estimate the influence of structure on shear behavior. [ABSTRACT FROM AUTHOR]

This paper aims to study structural differences and anti-erodibility properties of purple and loess soils in hilly terrains of southern and northern China. Yoder's method and Le Bissonnais method were used to determine the distribution of soil particle sizes, mean weight diameter (MWD), and geometric mean diameter (GMD). The sequences of water-stable aggregates in different sizes were as follows: On one hand, the sequence of purple soil aggregates was W2-5mm>W0.25-0.5mm>W0.5-1mm>W0-0.053mm>W0.053-0.25mm>W1-2mm>W>5mm. On the other hand, the sequence of the loess soil was W0-0.053mm>W0.053-0.5mm>W0.25-0.5mm>W0.5-1mm>W2-5mm>W1-2mm>W>5mm. Three LB treatments were carried out and the results were as follows: MWD and GMD of soil aggregates in the loess soil presented the trend of slow wetting (SW)>wetting stirring (WS)>fast wetting (FW), while those in the purple soil were WS>SW>FW. Under SW treatment, purple soil had higher erodibility factor (K) than loess soil, close to the result of Yoder's method. Yet under WS and FW treatments, K values of purple soil were much lower than that of loess soil (P<0.05). A significant difference in K, MWD, GMD, and soil organic matter (SOM) values was found between purple soil and loess soil (P<0.05). Slope positions greatly influence MWD, GMD, SOM content for the two soils (P<0.01), and the interaction between soil type and slope position showed an extremely significant positive correlation to MWD and GMD (P<0.01). Our study indicates that, under different breakdown mechanisms, purple soil has a more stable structure and higher anti-erodibility than loess soil. The results of this study will provide a theoretical basis for further understanding of the erosion mechanism of the main soils in China. [ABSTRACT FROM AUTHOR]

The development of agriculture in the arid and semiarid regions of China mainly depends on agricultural irrigation. Until 2016, water required for agricultural irrigation has accounted for more than 90% of the total water consumption. But traditionally extensive broad irrigation causes frequent loess geological hazards in irrigation area and it threatens security of local life and property. In this paper, we selected the Heifangtai irrigation district in Yongjing County, Gansu Province, where frequent instabilities occur, as the study area. We used laboratory tests and numerical simulation to examine the mechanism of loess landslides owing to the irrigation hydrological cycle. Irrigation changes the local natural hydrogeological conditions because of the loose and macroporous structure of loess. The numerous pores and fissures constitute preferential migration pathways of irrigation water; thus, irrigation can increase the groundwater level and hydraulic gradient. Broad irrigation is the main inducing factor of geological hazards (including landslides, collapses, and soil salinization) in arid and semiarid regions, and the development of fissures and sinkholes increases the risk of landslides. New water-saving irrigation methods need to replace the traditional irrigation methods and improve the utilization of water resources. A monitoring and warning system in susceptible areas should be established to ensure the sustainability of local agriculture. [ABSTRACT FROM AUTHOR]

As a natural foundation and fill material for construction in loess areas, there exists a significant impact on the stability of the engineering construction due to the permeation characteristics of the eolic sediment Malan loess. In this study, a series of air permeability tests were conducted for intact loess and remolded loess by using an improved air permeameter. We determined the influence of the water content, wetting and drying, dry density on the air permeability ka, and the use of microstructure models, scanning electron microscope (SEM) micrographs, and 3D super depth of field microscope micrographs to elucidate the microscopic mechanism of the air permeation. The results show that the air permeability ka of the remolded loess increased with the initial water content of remolding loess at dry density of ρd ≦ 1.6 g/cm3 increase, which is because of the formation of aggregates, and menisci water effect in loess; however, at dry density of ρd > 1.6 g/cm3, the air permeability started to decrease. The ka reduced remarkably as the water content of the intact and remolded loess increased during wetting process, and the air permeability during the drying process was always higher than the air permeability in the wetting process at the same water content. With the increase in the dry density, the air permeability of the remolded loess decreased; from a microstructural perspective, large and round pores tend to be small and elongated and irregular pores at high dry density. This paper will contribute to elucidating air permeability characteristics of loess and reducing the permeation risk in stability of the engineering construction in the Loess Plateau. [ABSTRACT FROM AUTHOR]

Sandy soil liquefaction is common phenomena in engineering construction. However, in fact, saturated or nearly saturated loess liquefaction is also common phenomenon in loess area. In recent decades, large earthquakes around the world are frequent, loess is widely distributed worldwide, and loess liquefaction is one of the hot issues in loess dynamics. China has the most typical loess landform in the world, and Chinese scholars have done in-depth research on loess liquefaction. In this paper, the phenomena, mechanism, influencing factors, microscopic characteristics, evaluation methods and prevention methods of loess liquefaction in China are reviewed systematically. At the same time, improvement of loess saturation technology and new theory of loess liquefaction proposed by Chinese scholars are also analyzed. The results indicated that damages of foundations, landslides and collapses are the main phenomena of disasters caused by loess liquefaction; shear capacity of soil particles due to friction is close to zero during loess liquefaction; the main influencing factors of loess liquefaction are effective confining pressure, load frequency, cyclic stress ratio, saturation, over consolidation ratio; most of soluble salts have been dissolved, which is one of the main causes of loess liquefaction, and structure of loess particles has also been destroyed; evaluation methods of loess liquefaction mainly include the standard method and the Seed–Idriss simplified discriminant method; pore water pressure and strain conform to "A type curve" in loess liquefaction; pile foundation reinforcement, dynamic consolidation, chemical treatment are the main prevention methods of loess liquefaction. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper draws on recent optically stimulated luminescence (OSL) dating to evaluate the long-held assumption that dust accumulation rates in the Loess Plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time, because both are controlled by the strength of the Asian monsoons and also possibly because the dunefields are proximal loess sources. The results show there is little evidence that high rates of loess accumulation coincided with well-dated episodes of extensive dune activity in the Mu Us, Otindag, and Horqin dunefields, at 11-8 ka and 1-0 ka. Explanations for the apparent lack of coupling include local variation in the trapping of dust and post-depositional preservation of the loess and dune sediments, in response to varying local environmental conditions. In addition, a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields. The results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale. The dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale, but the timing of late Quaternary dune activity, along with a variety of other evidence, indicates that moisture changes in many of the drylands of northern China may not be in phase with precipitation in core regions of the Asian monsoons. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Loess is a special geotechnical material with strong structural properties, and the microstructural characteristics of loess significantly influence its macroscopic physical features, mechanical properties, and catastrophic behavior. In this paper, serial samples were extracted from the continuous loess and paleosol strata of the Bai Lu tableland; with these samples, the optical microscopy-based serial sectioning method was adopted to study the quantitative characterization and variation in the loess microstructure. Three-dimensional characteristics and quantitative parameters of the particles, pores, and throats of the loess were obtained. The results indicate that the volume, Eq-Radius, and major-minor axis ratio of the loess particles satisfy third-order, third-order, and second-order Gaussian distributions, respectively. The Eq-Radius of the loess pores and throats satisfies a first-order Gaussian distribution, and the throat channel length satisfies a gamma distribution. With increasing stratum depth, the particles become more flattened, the throat radii become larger and the pore channels become slenderer. The variation in fitting parameters and the correlations between the macrophysical and mechanical properties of loess were then explored. The study of the microstructure of loess contributes to a better understanding of the catastrophic behavior of loess and the physical mechanism of geologic hazards in this area. [ABSTRACT FROM AUTHOR]