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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]

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]

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 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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

With the rapid development of railway construction in China, the role of passenger railway lines is becoming increasingly prominent. The construction of passenger railway lines is of great importance to the development of high-speed railways in Western China. Most regions in Western China are collapsible loess areas, and the collapsibility characteristics of loess are extremely unfavorable to foundation treatments. Therefore, the engineering properties of collapsible loess should be fully considered in foundation treatments, and corresponding treatment measures should be taken. In this paper, the displacement and stress characteristics of collapsible loess foundations are studied based on a test section of a subgrade treatment project in combination with engineering geology; this study aims to analyze several kinds of collapsible loess foundation treatment methods, such as single piles and group piles. The mechanism of the method is to make full use of the bearing capacity of the natural foundation, so that the soil between the piles is jointly to bear with pile, thereby the bearing capacity of the foundation is improved and the settlement of the foundation is effectively controlled. After the form of the composite foundation is selected, the foundation bearing capacity is improved by a parameter optimization design, and the foundation settlement is reduced, which eliminates the collapsibility of the loess. With field bearing tests, the rationality of the composite foundation design is verified. [ABSTRACT FROM AUTHOR]

Loess covers about one-tenth of the world's land area. While it is often used as embankment fill, loess is not an ideal construction material due to its wet collapsible nature, as it may cause significant embankment settlement and other related problems. Although explosive compaction (EC) technology has been used for many years, the challenges in experimental testing and theoretical analysis hinder its wider application. This paper contributes to the development of a design construction scheme of EC technology for loess embankment improvement through an integrated approach that involves finite element modeling, small-scale experiments, full-scale simulation and field implementation. In this study, a reliable finite element model is developed and validated through a small-scale experiment. The model is developed based on the software ANSYS/LS-DYNA®14.5 and takes into account the coupling between different materials (including soil, explosives, air and pavement). Critical performance factors such as the volume of the explosion cavity, the density of the compacted soil and the soil pressure can be obtained directly from the model. The model is then extended to simulate full-scale embankments. A sensitivity study is conducted to establish the correlations between the design parameters and the abovementioned performance factors. The relationships served as design guidelines for the successful implementation of the EC technique in an embankment section on the Cheng-Chao highway in China. The results demonstrated the feasibility of the EC technique as a ground improvement method for loess embankments, and it illustrated the effectiveness of the numerical method as a tool in design. [ABSTRACT FROM AUTHOR]

In March 15, 2019, a small-scale loess landslide occurred at Zaoling, Shanxi Province, China, destroying several buildings and killing 20 people. Based on a digital orthophoto map (DOM) and digital elevation model (DEM) derived from Dajiang Pro4 UAV aerial images, coupled with field investigations, this paper describes the geometric features of this slope failure and analyzes its possible inducing factors. Results show that this landslide has a circular chair shape with a sliding direction of 355°. The total projected area of the landslide is 11,800 m2, in which the source is 9880 m2, and the main scarp is 1995 m2. The volume of the source material and loose deposit debris are about 10 × 104 m3 and 12 × 104 m3, respectively. Our research suggests that the inducing factors of this event may include the low strength and structure of the loess under a wet condition, special landforms of the slope, and human activities such as water discharge from a nearby bath center building and coal mining. [ABSTRACT FROM AUTHOR]

Dali County is located in the eastern Weihe Basin where frequent ground fissure disasters occur. Dali ground fissures are macroscopically part of the ground fissure group in the Weihe Basin and have caused serious damage to infrastructure and agricultural production in this area. In this paper, 25 ground fissures in Dali County are identified through investigation, and two typical ground fissures in Fengcun and Weizhuang are selected for research. Through field investigation, trench excavation, geophysical exploration, soil water content tests and collapsibility coefficient tests, the basic features, shallow structural characteristics, deep structural characteristics and genetic mechanisms of the two ground fissures are revealed. The strike of the Fengcun ground fissure is 45°, almost parallel to the Shuangquan-Linyi Fault; the length is 2 km, and the profile is ladder-like and extends deep with synsedimentary characteristics. The Weizhuang ground fissures are circular in plan view with a length of 315 m and trumpet-shaped in profile; they disappear in the paleosol layer. The mechanism of the Fengcun ground fissure is related to basin extension and fault activity. The ground fissures are the surface reflections of deep faults. The mechanism of the Weizhuang ground fissures is related to loess collapsibility and seepage. The Malan loess has differential settlement in collapsible and noncollapsible areas, and ground fissures are the boundary line for differential settlement of loess. Finally, based on the genetic mechanisms of ground fissures, Dali ground fissures can be divided into two types: tectonic and nontectonic. [ABSTRACT FROM AUTHOR]

Loess tunnel erosion is a distinctive soil erosion pattern that commonly occurs in collapsible loess areas. The resulting soil erosion is a serious and complex problem. At present, most of the research methods on loess tunnel erosion are based on field investigation, and the knowledge obtained is, therefore, mostly qualitative. Erosion characteristics and erosion rates of loess tunnels are rarely revealed quantitatively by laboratory physical modeling or field investigation. In this paper, we report the results of a small model test based on three types of archetypal geological structures that are recognized by field investigation, i.e., vertical fractures, horizontal fractures, and round holes, These results reveal the effect of different initial flow cross sections on the erosion characteristics of loess tunnels. We found that, where water crosses an area of loess, waterfalls dominate initial erosion. We also studied the mud erosion rate to quantitatively reveal tunnel-erosion rates and their variation with time and found that tunnel erosion occurs in three stages: a rapid-erosion stage, an erosion slow-down stage, and a slow uniform-erosion stage. Using a model test to undertake quantitative studies into the relationship between the erosion rate of a loess tunnel and both initial dry density and initial water content, we demonstrated a significant linear negative correlation between these parameters. Through physical simulations combined with field investigation and analysis of survey results, we found that the erosion of loess tunnels occurs with a certain periodicity and that the tunnel-erosion base level plays a decisive role in the erosional features and final morphology of loess tunnels. By increasing our understanding of the internal mechanisms of loess tunnel erosion, our work will contribute to the prevention of cave erosion and reduction in the risks of associated disasters in the Loess Plateau of the Yellow River in China and in other loess-containing areas around the world. Our studies also provide a theoretical basis for carrying out soil and water conservation work in similar areas. [ABSTRACT FROM AUTHOR]

The structural, physical and morphological characteristics of loess will change as a result of the dissolution of mineral components, mainly carbonate, when it is exposed to acid rain, industrial acid leakage or other acidic environments. This study investigates the physical and structural characteristics of the Malan loess, Xi'an area, China, after carbonate dissolution. The presence of carbonate is determined by scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis. The loess was soaked with 0.2 mol/L acetic acid. The degree of degradation of the loess, carbonate and other minerals was determined by the abundances of elements in the solution. Microstructural analysis combined with the loess characteristics of adsorption, water stability, compressive yield stress and shear strength are used to explain the changes in the soil structure after carbonate dissolution. The results show that bonds in the cementation are irreversibly lost during the remoulding process, and additional bonds are destroyed with the removal of large amounts of carbonate, causing the skeletal particle surface area, specific surface area, adsorption capacity and water stability to decrease. The compressive yield stress and cohesion of the soil are considerably more sensitive at higher water contents. Calcium carbonate is the main carbonate component in the loess, and the secondary calcium carbonate connects the skeletal particles by coating and bridging; the strong cementation stops the particles from dispersing in water. The change in strength and deformation of the soil change its microstructure, which indicates that the secondary calcium carbonate affects the soil structure and stability by reducing the aggregate wettability and changing the mechanical strength of the soil aggregate. This paper will contribute to elucidating the formation and destruction of loess. [ABSTRACT FROM AUTHOR]

Currently, the theory and methodology of digital terrain analysis (DTA) has been well developed. However, this technique has not been widely applied in the research of loess landslides in China. This study investigated the application of DTA on loess landslides with the high-resolution terrain data obtained from low-cost unmanned aerial vehicles (UAVs). Taking a high-speed and long-runout landslide occurring on the Bailu Loess Tableland, a typical landform type on the Loess Plateau, as an example, we illustrated the fundamental characteristics and spatial patterns of the landslide from various perspectives and performed hydrology analysis, geomorphic change detection, hypsometric integral (HI) and stability analysis, morphology analysis, and structure analysis. The results prove that the DTA methodology cannot only advance understanding of the geomorphology and structure of landslides and detect geomorphic change but also reveal the evolution principles of landforms and demonstrate unique advantages in the prediction of the internal stability of landslides. In conclusion, the DTA methods adopted in this paper are useful to better understand loess landslide and its relationship with geomorphologic evolution. [ABSTRACT FROM AUTHOR]

Rainwater is the main water source in arid and semiarid areas of the Loess Plateau, where rainfall is generally insufficient, ineffective and underutilized during the growing season. Thus, improving rainwater utilization efficiency is essential for sustainable agricultural development. A new system composed of rainwater harvesting, an infiltrator bucket with multiple holes and mulching (RHM), was designed to maintain soil moisture at a proper level in rain-fed orchards in arid and semiarid areas of the Loess Region of China. However, there is a lack of clarity on the effectiveness of RHM. In this study, changes in the soil environment and the growth and physiology of apricot trees were monitored via two treatments: (1) Rain-harvesting irrigation system (RHM) treatment and (2) traditional orchard treatment (CK) as a baseline. The results showed that (1) RHM could effectively improve soil water storage at depths of 0–45 cm and at a horizontal distance of 40 cm from the trunk. For the 1.4 mm light rain event, the soil water content increased by 6.3–12%, and for the two moderate rains, the soil water content increased by 12–25%. The change in the soil relative water content predicted by the LSTM model is consistent with the overall trend of the measured value and gradually decreases, and the prediction accuracy is high, with an error of 0.65. (2) The average soil temperatures at 5 cm, 20 cm and 40 cm under RHM were 17.0% (2.4 °C), 13.6% (1.9 °C) and 7.5% (1 °C) greater than those under CK, respectively. (3) Compared with the control treatment, RHM improved the growth and WUEL of apricot trees. The results highlighted the efficiency of the RHM system in enhancing the soil environment and regulating the growth and physiology of apricot trees, which has greater popularization value in arid and semiarid areas. [ABSTRACT FROM AUTHOR]

The cycle of precipitation change is key to understanding the driving mechanism of the East Asian summer monsoon (EASM). However, the dominant cycles of EASM precipitation revealed by different proxy indicators are inconsistent, leading to the "Chinese 100 kyr problem". In this study, we examine a high-resolution, approximately 350,000-year record from a low-latitude loess profile in China. Our analyses show that variations in the ratio of dithionite−citrate−bicarbonate extractable iron to total iron are dominated by the ~20-kyr cycle, reflecting changes in precipitation. In contrast, magnetic susceptibility varies with the ~100-kyr cycle and may be mainly controlled by temperature-induced redox processes or precipitation-induced signal smoothing. Our results suggest that changes in the EASM, as indicated by precipitation in this region, are mainly forced by precession-dominated insolation variations, and that precipitation and temperature may have varied with different cycles over the past ~350,000 years. Earth's orbit has tuned the variations of the East Asian summer monsoon. Here, a low latitude loess palaeoclimate record provides evidence that variation in monsoon rainfall is dominated by the precession cycle. [ABSTRACT FROM AUTHOR]

The South Jingyang tableland, located in Shaanxi Province, China, is composed of loess deposits. Agricultural irrigation in this area has caused the continuous rise of the groundwater table, which triggered a series of loess landslides. Although extensive research has been conducted on the effect of rising groundwater tables on induced loess landslides, less is known about the groundwater table distribution. This study jointly investigated the distribution of the groundwater table in the South Jingyang tableland using boreholes, electrical resistivity tomography (ERT), and laboratory tests. A qualitative analysis between the apparent resistivity and the water content was estimated at different depths, using the borehole data and ERT inversion data. A quantitative relationship between the resistivity and the water content was established in the laboratory tests. A combination of the qualitative analysis of the inversion results and the quantitative relationship was used to determine the distribution of the groundwater table. The groundwater table is present at the depth where the water content of the loess is 30% (liquid limit of loess) and the resistivity is 28.35 Ω m. The groundwater table elevation in the southern study area is higher than that of the northern study area and decreases in a stepwise gradient from south to north. This study not only identified the distribution of the groundwater table in the South Jingyang tableland, but also makes up for the limitation and inaccuracy in determining groundwater tables by relying solely on the borehole information or inversion results of ERT. The ascertained distribution characteristics of the groundwater table provides a basis for the analysis of the formation mechanism of landslides. [ABSTRACT FROM AUTHOR]

Developing a method for quickly estimating the cumulative infiltration in shallow slopes is essential for engineers to evaluate slope stability. In this paper, the hydraulic parameters of the Yan'an loess in China were obtained through physical mechanics test. Numerical experiments with different slope inclinations, soil thicknesses, rainfall intensities, and initial moisture contents were carried out to obtain the cumulative infiltration curves. The Philip model was used to fit the cumulative infiltration curves. The slope inclination, soil thickness, rainfall intensity, and initial moisture content were served as the input variables, and the parameters of the Philip model were the output variables. A generalized regression neural network–based method was proposed to estimate the cumulative infiltration quickly. Three indicators (coefficient of determination, mean squared error, and mean absolute error) show that the performance of the proposed method is superior to those of the multiple linear regression model, the back propagation neural network, and radial basis function neural network. Parametric analysis indicates that rainfall intensity is the most sensitive parameter affecting cumulative infiltration. [ABSTRACT FROM AUTHOR]

To control the deformation disaster and explore the effective in-situ evaluation method of filling in the Loess Plateau of China, the laboratory tests and cone penetration test (CPT), dynamic penetration test (DPT), standard penetration test (SPT) were carried out for a case of filling with large area. The research was performed based on data distribution, non-uniformity evaluation, correlation and sensitivity analysis. The results are as follows: (1) the filling filled by layered compaction still has non-uniformity. The distribution of CPT tip resistance is consistent with collapsibility coefficient and obeys logarithmic normal distribution. The distribution of CPT side friction and SPT hammer number are consistent with moisture content, void ratio and dry density and obey normal distribution. The distribution of DPT hammer number does not correspond to any soil properties index. The CPT also has the advantages to reflect layered compaction characteristics along filling depth and distinguish the boundary between filling and undisturbed soil. (2) Three test methods can all reflect the non-uniformity of soil properties in depth direction. However, for the horizontal direction, the CPT results can best reflect non-uniformity of actual collapse deformation, followed by SPT and DPT is the worst. (3) For the testing of filling compaction state, CPT tip resistance and SPT have good mathematical correlation, and the sensitivity of CPT tip resistance is significantly higher than other methods. For the testing of filling collapse deformation capacity, the CPT tip resistance, DPT and SPT all have good correlation and sensitivity. So CPT tip resistance has the best cooperation between correlation and sensitivity. (4) The CPT (especially tip resistance part) can be effectively applied to the properties evaluation of silty loess filling. The tip resistance to void ratio and collapsibility coefficient follow the exponential function and logarithmic function respectively. [ABSTRACT FROM AUTHOR]

The erosion of engineered slope surfaces has become an urgent problem in loess regions in China, which has a serious impact on the safety and stability of the slope projects. In this paper, to study the effect of the confining pressure, dry density of the slope surface, and water flow velocity during wetting procedure on the erosion characteristics of compacted loess, we developed a laterally confined uniaxial compression-erosion apparatus, which was characterized by the fact that it can change the confining pressure of the being eroded soil sample to analyze the loess erosion rates and particle size distributions of the eroded sediments. The fractal dimensions of the eroded sediments were calculated by fractal theory and their variations were analyzed. Results show that the erosion rate is approximately linearly related to the confining pressure. The higher pressure has a tendency to move towards the free top of soil sample, the erosion rate increases. Compared with the water flow velocity, the higher confining pressure plays a greater role in the erosion rate, the influence of water flow velocity on the erosion rate decreases. With the increase of dry density, the erosion rate decreases, the higher dry density enhances the ability of soil sample to resist water erosion. The confining pressure changes the particle size distribution of the eroded sediments of loess samples, the median diameter D50 increases. However, the fractal dimension decreases with the increase in confining pressure. The confining pressure of slope surface has a negative effect on the loess anti-erosion characteristics. The results in this paper would provide detailed information on the mechanisms of loess erosion, which could contribute toward prevention of surface erosion of high fill slopes in loess regions. [ABSTRACT FROM AUTHOR]

In this paper, nine sediment sequences in the inner desert, desert-loess transitional zone (agro-pastoral transitional zone) and the northern margin of the Loess Plateau were investigated to study the sediments of Mu Us (Maowusu) and Otindaq (Hunshandake) sandy land in northern China since the last glaciation. All of these sequences consisted of the upper Holocene dark paleosol and the lower aeolian sand formed during the last glacial stage. The Mu Us and Otindaq sandy land became the active desert since the last glaciation and covered a larger sandy area than at present. Mu Us sandy land began to show a landform of sandy desert and expanded southward towards the northern boundaries of the Loess Plateau. The Holocene was characterized by the advent of warmer and wetter climatic conditions in northern China, resulting in the rapid growth of surface vegetation and Mu Us and Otindaq sandy land became a steppe. The thickness of surface soil reached up to as much as 50–80 cm. Thick paleosol covered the drift sands, and served as a protective layer for the steppe and farmland. Although the last glacial cycle is far away, paleo-aeolian sands formed during that period are still the material sources of regional desertification. Unreasonable cultivation destroying the Holocene paleosol, combined with dry climate and strong wind would result in activation of paleo-aeolian sand leading to the desertification of the study areas. [ABSTRACT FROM AUTHOR]

In this study, the land desertification of transitional zones of desert loess in the Yulin region (China) is studied from TM images in a geographical information system (GIS). It is found that the desertification in Yulin is still severe. The desertified land accounts for 67.7% of the total land areas. The distribution of desertified land shows obvious spatial imbalance, with severe desertification in northwestern regions and slight desertification in southeastern regions. This imbalance is related to the difference in physical factors and land-use pattern. The process of desertification in Yulin areas shows a steady and even reversed trend between 1987 and 1999, as a result of positive efforts. At the end of the paper the cause of desertification is discussed. It is believed that the interaction and confliction between the natural process and human activities may lead to the development of desertification. [ABSTRACT FROM AUTHOR]

Gully erosion is widespread in central China's ecologically fragile loess plateau. However, research on the monitoring and evaluation of large-scale erosion is scarce. Here, we collected 16 pairs of Sentinel-1A images from the rainy season, spanning April 5-October 26, 2019, subsidence is then quantified and its results can indirectly reflect the intensity of erosion on the largest loess plateau in China, the Dongzhiyuan tableland, using small baseline subset synthetic aperture radar interferometry (SBAS-InSAR). The results showed that, the average erosion rate was 9 mm/year, throughout the study area, Surprisingly, the average erosion rate in the gully reached 160 mm/year, the sides of the gully correspond to the most extensive and intense erosion. Heavy rainfall, slope gradients below 15°, changes in groundwater levels due to freeze–thaw action and water infiltration during rainfall, and lack of vegetation due to continued gully side erosion, drive the intense erosion. These results demonstrate the reliable ability of the SBAS-InSAR method in accurately assessing large-scale gully erosion. The InSAR-calculated subsidence demonstrates a strong predictive capability for soil erosion and is generally consistent with previously observed levels of erosion, although much noise interference also occurs. Therefore, in the future InSAR-calculated sedimentation could be used as an indirect measure of erosion levels at multiple watershed scales. [ABSTRACT FROM AUTHOR]

Purpose: Inherent spatial variability of properties of loess deposit along depth direction plays important roles in soil reclamation, agricultural irrigation, and risk assessment and management of geo-hazards on the Loess Plateau. This study aims to develop a database for loess deposit properties in Shaanxi Province first, followed by evaluating and reporting comprehensively the abovementioned spatial variability along depth. Materials and methods: A comprehensive literature review and numerous laboratory tests were conducted for 37, 81, and 177 loess profiles respectively for sandy, silty, and clayey loess to examine their properties in Shaanxi Province, China. For each property collected in the database, the means, coefficients of variation (COV), most suitable probability distribution functions, and spatial correlation lengths along the depth direction were evaluated and reported. Results and discussion: The physical and index properties and strength properties of the three loess soil generally exhibit relatively low variabilities with a mean COV of less than 20.0% in most cases. In contrast, the deformation properties exhibit medium to high variabilities with a mean COV varying from roughly 27.0 to 85.0%. For all of these properties mentioned above, the spatial correlation length along depth was estimated to be approximately 3 ~ 8 m. Conclusions: (1) The COV of loess properties at one site can be significantly different from that at other sites. Thus, the site-specific variabilities of loess deposit properties shall be considered in geological design and analysis. (2) When site-specific data of properties for loess deposits are not available for on-going geological/geotechnical projects, the typical ranges of loess properties obtained in this study, including their statistics and correlation lengths, can be used as guidelines for approximation. [ABSTRACT FROM AUTHOR]

Permeability tests are performed by using the flexible wall permeameter to study the influence of bentonite-HDTMA (hexadecyl trimethyl ammonium bromide) on the permeability performance of Loess as a lining material in the solid waste landfill. Results show, the impermeability of compacted Loess in the middle and lower reaches of the Yellow River in China does not meet the standard requirement as the landfill liner. The permeability of Loess mixed with more than 10% bentonite ratio is less than 1.0 × 10−7 cm·s−1. The permeability of Loess increases slightly after mixing a small amount of HDTMA. The impermeability of Loess mixed with some bentonite-HDTMA ratio still meet the standard requirement. The HDTMA may destroy the soil aggregate structure and increase the soil permeate channel. The SEMs show that the bentonite clay particle can fill the pores between Loess coarse particles and improve the impermeability performance of the material. The digital photos show that HDTMA can effectively resist the development of soil macro-cracks induced by wetting–drying cycles, better for liner to maintain good impermeability. On this basis, the relationship between the hydraulic conductivity of bentonite-HDTMA modified Loess and dry density is constructed. From this study, Loess can be used as a lining material for landfills, when mixed with bentonite/HDTMA at ratios of 10%/0% or 14%/2%. [ABSTRACT FROM AUTHOR]

Loess landslides pose significant physical and environmental threats to communities of the Heifangtai Terrace in Gansu Province, China. Estimating potentially affected areas using dynamic numerical simulations provides a foundation for risk assessment and management. However, current studies often use rheological input parameters derived from the back analysis of an individual historical landslide, which requires that the potential landslide is quite similar to the historical landslide to guarantee the accuracy of predictions. We collected data from 20 loess flowslides that occurred from 2015 to 2019 in the Heifangtai Terrace. A friction model embedded in MassFlow was used to simulate run-out behavior. Accumulation depths at multiple control points were used as observation information. A multi-objective optimization back analysis was used to calibrate optimal rheological parameters for each flowslide, yielding a region-specific database of 20 datasets for statistical analyses. Finally, two flowslides that occurred in 2019 were employed as potential landslides to conduct probabilistic run-out predictions based on the database. These predictions agreed well with the observed accumulation areas in both cases, thus validating our method. This database will be useful for future landslide run-out predictions in this area. [ABSTRACT FROM AUTHOR]

Agricultural irrigation of the South Jingyang tableland in Shaanxi Province, China has led to a continuous rise of the groundwater level and has triggered a series of loess landslides, thereby seriously affecting the life and property safety of local residents. Research shows that the major cause of the landslide in the loess layer of the South Jingyang tableland is the rising groundwater level. Therefore, the research on the formation mechanism of landslide in this area should include the investigation of the stratigraphic structure and groundwater level distribution characteristics. On this basis, a series of approaches, such as electrical resistivity tomography (ERT), borehole, and laboratory tests, was carried out on the South Jingyang tableland, and the groundwater level distribution and stratigraphic structure in the study area were determined. The qualitative relationship between resistivity value and water content at different depths was detected using the inversion results of ERT and borehole data. Through laboratory tests, the quantitative relationship between resistivity values under different water contents was established. The precise depth of the groundwater level was inferred by connecting the qualitative relationship with the quantitative relationship, and then a detailed 3D geological model was established by linking the inversion results of ERT with the field borehole lithology data and geological survey data. The detection results show that when the qualitative and quantitative analyses of the ERT inversion results were combined, the distribution of the groundwater level was accurately judged. The ERT is effective in reflecting the stratigraphic structure and hydrological characteristics of the Loess Plateau, and its potential as a supplementary technology for detecting the groundwater level is reasonable. This study addresses the limitation and inaccuracy in determining the stratum structure and groundwater level by solely relying on borehole information or ERT. The established 3D geological model not only provides a basis for the study of groundwater table fluctuation, but also a technical guidance for the stability evaluation of loess slope, landslide prediction, and early warning in the study area. [ABSTRACT FROM AUTHOR]

Spontaneous combustion of coal seams can produce a high temperature of about 800 ℃, which greatly changes the thermal conductivity of the overlying loess layer. The thermal conductivity of loess plays an important role in ecological restoration design and the calculation of roadbed and slope stability. In this study, loess in northern Shaanxi, China was taken as the research object to measure the mass-loss rate and heat conduction parameters of loess specimens after high temperature. The test results show that, between 23 and 900 °C, with temperature increasing, the mass-loss rate is reduced. And the heat conduction coefficient (λ), specific heat capacity (c), and thermal diffusion coefficient (α) decreased by 48.9%, 23.1%, and 35.6%. This is due to the air thermal resistance effect caused by the increase of pores and cracks in loess specimens after high temperature. [ABSTRACT FROM AUTHOR]

To study the influencing factors of surface subsidence by the backfilling of a mined-out area on thick and loose loess layers, a mechanical model on synergic deformation and surface subsidence is constructed taking the case of a sedimentary bauxite mine in China's Shanxi province as an example. Backfill state is classified based on the position of the protective roof and the backfill body. The influence of different filling ratios, the thickness of overlying loess, and the stope span on surface subsidence are quantitatively analyzed. The results reveal that: (1) When the thickness of the overlying loess Hg and the stope span s are constant, surface subsidence ωmax is negatively correlated with the filling ratio η. When η reaches the state III inflection point, the amplitude of surface subsidence ωmax declines sharply and eventually tends to be stable. (2) When the filling ratio η and stope span s are constant, surface subsidence ωmax is negatively correlated with the thickness of the overlying loess Hg, and the growth ratio decreases continuously. (3) When η and Hg are constant, surface subsidence ωmax is positively correlated with s, and the growth ratio increases continuously. In the end, the validity of the theoretical calculation is verified by numerical simulation and an engineering case example. [ABSTRACT FROM AUTHOR]

The stability classification of loess deposits around tunnels is a vital prerequisite for safe construction in underground environment. Due to the fuzziness and randomness of loess physical and mechanical parameters, the stability prediction of loess deposits shows uncertainty. Existing loess deposit stability classification models rarely consider the uncertainty of influencing factors. A novel classification probability model of loess deposits is proposed for the above problems based on Monte Carlo simulation and multi-dimensional normal cloud (MCS-Cloud). Specifically, five loess parameters, including water content, cohesion, internal friction angle, elastic modulus, and Poisson ratio, were selected as predictors for the stability level of loess deposits. The weights of the predictors were obtained through 50 test samples. After acquiring the numerical characteristics of the normal cloud, the stability level can be comprehensively evaluated with the weighted multi-dimensional normal cloud model. The classification model was applied to the loess tunnel in Yan'an, China. The prediction results are in good agreement with practical engineering, denoting the rationality of the weighted multi-dimensional normal cloud. Finally, the stability classification of loess deposits was discussed from the perspective of uncertainty analysis with the application of MCS. Results proved that the MCS-Cloud model is feasible for classifying the stability of loess deposits surrounding tunnels. The obtained classification probability can be used for quantitative risk assessment of loess tunnels. [ABSTRACT FROM AUTHOR]

Loess landslides are widely distributed in Northern China and pose a significant threat to human life, natural resources, and infrastructure in mountainous regions. Accurate segmentation and measurement of loess landslides is crucial to documenting their occurrence and extent and investigating the distribution, types, and patterns of slope failures. The measurement of landslides also assists in assessing their susceptibility and risk. Herein, a novel loess landslide segmentation and measurement framework based on deep learning is proposed. Multiple experts label the ground-truth landslide regions, and simultaneous truth and performance level estimation (STAPLE) masks are generated. The U-Net segmentation algorithm is trained using a supervised approach to segment the loess landslide region. The fully connected conditional random field is integrated into the U-Net to further optimize the segmentation quality. In the final step, the predicted landslide boundaries are visualized, and the diameters (e.g., length and width) of the segmentation outcome are computed simultaneously. Four state-of-the-art segmentation algorithms are selected for the comparative analysis. The computational results demonstrate that the proposed framework outperforms all the other algorithms tested in terms of segmentation accuracy and boundary errors. The results verify the advantages of using STAPLE and U-Net integrated with a conditional random field. [ABSTRACT FROM AUTHOR]

Microstructural changes in the loess deposits due to the presence of joint planes is one of the primary causes of the geohazards (ground fissures, ground subsidence, landslides, collapses, and soil and water losses) that occur in the loess regions of western China. By means of uniaxial tensile tests and triaxial shear tests conducted under different confining pressures, we tested fractured loess Q samples with five fracture plane inclination angles (0°, 30°, 45°, 60°, and 90°) taken from Sanyuan County, Shaanxi Province in western China, where geohazards are prevalent. Analysis of the tensile stress-strain and shear stress-strain relationships of the fractured loess specimens revealed the characteristics of the fractures that induce instability in this area. These results provide important baseline data for future research on the mechanism of geohazards in the loess regions of western China. [ABSTRACT FROM AUTHOR]