The Loess Plateau is a major engineering intensive and energy producing region in China, where landslide risk has become increasingly prominent. Therefore, landslide susceptibility assessment is of great importance for ensuring regional safety and sustainable development. However, most existing landslide susceptibility models focus on improving prediction accuracy while neglecting the spatial heterogeneity of landslide occurrence. In this study, Yaozhou District, China, was selected as the case study. A dataset comprising 16 conditioning factors related to topography, geology, land use, and vegetation coverage was constructed. Two spatial heterogeneity aware models, namely geographically weighted random forest (GWRF) and geographically weighted categorical boosting (GW-CatBoost), were developed based on geographically weighted regression. These two models were compared with traditional global machine learning models, namely random forest (RF) and CatBoost, in terms of landslide susceptibility prediction performance. In addition, SHapley Additive exPlanations (SHAP) analysis was used to interpret the contributions of conditioning factors in each model.The results showed that vegetation coverage, human activity and road related factors were the dominant conditioning factors of landslides in the study area, and that the geographically weighted models further revealed distinct spatial variations in the dominant conditioning factors and local landslide controlling mechanisms. A unified evaluation framework including AUC, confusion matrix, and derived metrics was adopted. GW-CatBoost achieved the highest AUC point estimate of 0.926 and performed favorably across most confusion-matrix-derived metrics. The performance of both geographically weighted models remained relatively stable when the number of retained conditioning factors was reduced from 13 to 8, while GW-CatBoost maintained an AUC of approximately 0.87 with 5 dominant factors. The proposed framework addresses a key limitation of global machine learning approaches, which assume constant effects of conditioning factors across space, and reveals spatially heterogeneous patterns of factor sensitivity across subregions. Its flexible factor configuration and regionally adaptive structure also provide potential for application in other geographical contexts. These findings provide a scientific basis for refined hazard management and regional development planning in the Loess Plateau area.

In the Loess Plateau of China, loess creep characteristics with time effects are crucial factors influencing slope stability. Especially under extreme climates, after being subjected to repeated dry-wet cycles (DWC), the creep deformation of loess is more intense, leading to large-scale and frequent disasters such as landslides. In this study, a series of direct shear creep tests was performed on the loess samples after dry-wet cycles to understand the effect of DWC on loess creep characteristics profoundly. The results show that the loess is more vulnerable to creep failure after being subjected to dry-wet cycles; the greater the normal stress of the loess, the more pronounced the effect of dry-wet cycles, and the more significant the creep deformation under shear stress. Moreover, the long-term shear strength of loess decreases exponentially as the DWC increases. Based on the Burgers model, a new nonlinear viscoelastic-plastic rheological model (NVPM model) is proposed, which can accurately describe the entire loess creep curve under the effect of dry-wet cycles, especially for the accelerated creep stage that the Burgers model cannot fit. Based on the shear creep test results, the creep parameters obtained from the NVPM model were applied to a numerical simulation of a typical loess slope. The results reveal that the NVPM model is capable of reasonably explaining the stability deformation law of a loess slope under the coupling effect of DWC and creep, and the causes of loess landslides. The research results can provide a theoretical reference for the long-term stability analysis and prediction of loess slopes.

Geological hazards on the Southern Chinese Loess Plateau (SCLP), particularly loess-mudstone landslides (LMLs), are increasingly triggered by extreme climatic events. This study investigates the climatic controls on the stability of the Doujitai landslide within the active Weihe Fault Zone, a representative LML in the SCLP. A series of ring shear tests were conducted on remolded loess from the landslide’s slip zone to quantify the degradation of shear strength parameters under varying water content, normal stress, shear rate, and shear modes. The results revealed that the remolded peak and residual shear strengths first increased and then decreased with increasing water content, accompanied by a transformation from strain hardening to strain softening. The remolded peak strength increased significantly with shear rate, while residual strength first decreased and then increased. Increasing shear rate also enlarged the amplitude of residual shear stress fluctuation. Compared with single-stage tests at different normal stress levels, multi-stage shear led to an attenuation of internal friction angle. Based on the experimental data, a hydro-mechanically coupled numerical analysis was conducted to model the slope’s stability evolution during rainfall. The results show an obvious relationship between the dip angle of the mudstone-loess interface and slope stability. Furthermore, the impact of rainfall intensity and duration on stability was evaluated, highlighting that higher intensity rainfall drastically accelerates stability degradation. This study elucidates the formation mechanism of LMLs under climatic control, emphasizing that extreme rainfall acts as the critical external trigger of slope instability within a tectonically preconditioned geological setting.

The Yellow River “Ji-shaped Bend” region, a distinctive energy-rich zone in northern mid-latitudes, holds unique scientific significance for global studies of geological resources and loess-related hazards. Characterized by complex geology and fragile ecology, this area now experiences frequent coal-mining-induced geohazards that form loess disaster chains (LDC), that severely threatens local safety, ecology, and sustainable development. In this study, the loess disaster chain at Anshan Coal Mine was examined, analyzing its topographical features, development patterns, and disaster mechanisms. It investigates how the physical and mechanical properties of loess change under varying water contents and compaction levels. Additionally, this study explores the key factors and dynamic processes that drive the disaster chain and reveals its underlying disaster mechanisms. Findings show that after saturation, loess samples experience notable reductions in shear stress, cohesion, and internal friction angle, with cohesion decreasing the most. Comparative experiments demonstrate that lower compaction result in higher permeability and faster disintegration. The primary factors influencing the disaster chain include loess properties, extreme rainfall, geological structure, coal mining, and improper excavation, with extreme rainfall identified as the main trigger at Anshan Coal Mine.Based on these findings, the disaster chain evolution at Anshan Coal Mine progresses through five stages: 1) loess fissure formation, 2) loess landslide occurrence, 3) landslide transformation into debris flow, 4) debris flow erosion and expansion, and 5) debris flow accumulation. This study provides scientific insights for sustainable energy development and disaster prevention, while offering valuable references for disaster chain research in similar geological settings.

Loess-red bed interface landslides occur frequently in Northwest China, and the critical conditions for their initiation are closely related to the dynamic evolution of the shear strength at the contact interface. To investigate the initiation mechanisms of such landslides, this study takes the slip zone soils of typical loess-red bed interface landslides as research objects. Through ring shear tests and scanning electron microscopy (SEM) analyses conducted on three types of samples (pure loess, pure red bed, and loess-red bed composites) the study systematically evaluates the evolution of shear strength and microscopic structures under varying normal stresses, water contents, and shear rates. The results show that: (1) The peak and residual shear strengths of all three soil types increase markedly with increasing normal stress. The peak shear strength exhibits a unimodal variation with water content and shows a slight increasing trend with increasing shear rate. (2) The loess-red bed composite samples are most sensitive to water content changes, with the most significant strength attenuation. Their brittleness index reaches 15.6%, significantly higher than that of the single-component soils, indicating a stronger tendency toward strain-softening failure. (3) Microscopic observations reveal that increasing water content weakens cementation of clay particles, and the enhanced lubricating of flaky minerals promotes the formation of smooth shear surfaces, leading to a significant reduction in interfacial shear strength. Integrating field investigations with laboratory tests, the initiation mechanism of loess-red bed interface landslides is clarified. The hydraulic weakening effect of the loess-red bed interface is identified as the core mechanism controlling slope instability.

In recent years, the continuous advancement of engineering construction in China's Loess Plateau region has resulted in numerous high-fill and deep-excavation loess-red layer composite slopes (HDLS). Rainfall infiltration, a primary factor influencing slope stability, has markedly increased the likelihood of landslide disasters. To investigate the primary sliding failure mechanism of HDLS, a series of physical model tests and numerical simulation analyses were conducted on a loess-red layer composite slope in Zhongliang Town, Tianshui City. The study systematically examined the infiltration characteristics, deformation response, crack extension, and failure patterns of HDLS under rainfall conditions. The results demonstrate that (1) analysis of monitoring data from multi-sensors and real-time slope imagery revealed that under constant rainfall intensity, the slope failure process accelerates significantly with increasing slope height and angle. Furthermore, the slope shoulder exhibits greater susceptibility to large-scale sliding deformation due to enhanced rainwater infiltration. (2) Numerical simulations using Geo-studio reveal that the slope safety factor decreases significantly under fill and excavation conditions. The safety factor of high-fill slopes exhibits a slower decline with prolonged rainfall duration. (3) Rainfall erosion readily develops gully sliding ways on fill slopes, with tension cracks in the mid-slope region serving as primary infiltration channels that constitute the dominant failure reason. As the excavated slope angle increases, both the slope toe and mid-slope experience significantly enhanced unit water flow, intensifying surface runoff erosion, and the failure pattern exhibits progressive upward development originating from the slope toe to the upper slope. This paper investigates the hydrologic response characteristics and sliding deformation mechanisms of HDLS under various working conditions. The findings provide a significant reference value for protecting such high and steep slopes.

Accumulation landslide induced by rainfall is one of the most important types of geological disasters in the Qinling-Bashan Mountains, China. In recent years, nearly one hundred accumulation landslides have caused significant casualties and serious economic losses. To better understand the response mechanism of sliding zone soil to such landslides under rainfall infiltration conditions, the landslide in Zhashui County, Shaanxi Province, was taken as a typical case. The field investigation, ring shear test and creep test were carried out using sliding zone soil. Combined with the laboratory tests results, the landslide was numerically simulated and analysed. Laboratory test results show that the increase in moisture content leads to a reduction in the shear strength of the sliding zone soil, promoting slope creep and accelerating the deformation of the slope. Numerical simulation results for two typical rainfall infiltration scenarios, short-duration heavy rainfall and long-duration weak rainfall, indicate that the failure type of accumulation landslide is a creep-slide failure, and the damage degree of the heavy rainfall to the slope is greater than that of the weak rainfall. According to the results of the field investigation and numerical simulation, we find that the mechanical behaviour of the sliding zone soil controls the failure mode of the accumulation landslide in Qinling-Bashan Mountains. This kind of landslide has roughly experienced three failure stages: the early disaster-breeding stage, the interim accelerated deformation stage and the anaphase instability failure stage.

The occurrence of landslides is often a complex dynamic evolution process, characterized by multiple slide-stop-slide cycles. Each state transition may be associated with changes in the mechanical state and structure of the sliding zone soil, significantly influencing the overall stability of the landslide. Taking the sliding zone soil of Ertaizi gully landslide as test material, a series of repeated ring shear tests were conducted under different moisture contents (Mc), normal stresses (σn), and the number of shear cycles (NSC) to investigate the mechanical strength characteristics of the sliding zone soil during the process of repetitive motion landslides movement. The results indicate: (1) Mc critically influences the soil shear strength in the deep sliding zone, while increasing NSC diminishes the strain-softening phenomenon of soil. Additionally, the attenuation effect of NSC against shear strength actually weakens the cohesion of the soil. (2) An increase in Mc reduces soil looseness near the shear plane, while an increase in σn expands relatively flat region adjacent to the shear plane. Under shearing, soil particles align along the shearing direction, exhibiting a preferred orientation within 0 30°. (3) Although there is a healing mechanism at the shear plane, repetitive motion landslides remain highly hazardous. This research offers a theoretical basis for comprehending the effects of Mc, σn, and NSC on the mechanical strength and microstructural deformation properties of soil. Additionally, it provides guidance for predicting the stability of repetitive motion landslides.

Loess landslides caused by the freeze-thaw cycle (FTC) have become increasingly frequent. In this study, a typical loess landslide in the seasonal freeze-thaw area was taken as the research object. Triaxial creep tests and scanning electron microscope tests were conducted on the undisturbed loess after FTC. The effects of FTC on the creep characteristics, long-term strength, and microstructure of loess were revealed, and the mechanism of FTC-induced loess landslides was discussed as well. The results show that (1) after FTC, the creep deformation of the sample noticeably increases, and the influence of FTC on the shallow loess is greater. (2) The long-term strength of loess after FTC obviously decreases. As the FTC times rise, the long-term strength initially declines, then increases, and then decreases again. The deterioration effect of FTC on shallow loess is more pronounced. With the increase in moisture content, the long-term strength of loess decreases, and the FTC action gradually weakens the strength difference caused by the change in moisture content. (3) The microstructural analysis of loess samples revealed that FTC results in the change of loess microstructure, the weakening of particle cementation, and the instability of particle contact. (4) FTC leads to the accumulation and evacuation cycle of groundwater in the slope. The formation process of freeze-thaw loess landslides is divided into initial stability stage, freeze-thaw deterioration stage, fracture development, and sliding surface formation stage and slope instability stage. The research results provide a new understanding for the study of loess creep characteristics and the formation mechanism of loess landslides.

The large number of fissures developed in loess affect the creep mechanical properties of the soil body, easily triggering geologic disasters such as loess landslides. To gain a comprehensive understanding of the creep characteristics of fissured loess, we used the undisturbed loess from the landslide group in the Heifangtai area of Gansu Province, China, to conduct triaxial creep tests under various prefabricated fissure angles (without fissure, 30 degrees, 45 degrees, 60 degrees, and 90 degrees) and different matric suction conditions. The stress-strain-time characteristics of fissured loess are analyzed, and the long-term strength variation law of fissured loess is determined. The deterioration effect of loess fissures is revealed, and the creep deformation characteristics of fissured loess samples (FLS) are explored. The results show that: (1) The deviatoric stress, confining pressure, and matric suction significantly affect the creep deformation of fissured loess and the duration for the sample to attain steady-state creep. (2) The fissures have a pronounced deteriorating effect on the long-term strength of loess. As the fissure angle increases, the long-term strength of the loess sample initially decreases and subsequently increases, exhibiting a "V" shaped variation, while the cohesion demonstrates a comparable "V" shaped variation. (3) The deterioration coefficient of the fissure initially rises and subsequently declines with increasing confining pressure. (4) The creep deformation characteristics of FLS are categorized into axial deformation, bending deformation, and torsional deformation. Generally, the fissure angle affects the axial strain of the sample; however, an increase in confining pressure weakens the influence degree of the fissure on the deformation. The findings provide new insights into theoretical support for the study of loess mechanics and deformation characteristics in the Loess Plateau region of China. This is significant in elucidating the effect of fissures on the occurrence and development of loess landslide disasters.

The prominent tectonic activity occurring in the southern margin of the Chinese Loess Plateau (SCLP) has resulted in the widespread development of loess-mudstone landslides (LMLs) along the fault zone. To elucidate the failure mode of LMLs under the action of a geological environment shaped by fault activity, a series of physical model tests was conducted considering various slope structures (contact angles), topographic features (slope gradients), lithology composition (loess layer thicknesses), erosion morphologies, and rainfall intensities. Multi-sensor monitoring and topographic data extraction revealed that geological environmental factors, such as specific slope structure, topography, and lithology shaped by fault activity, exert significant control over the stability and failure mechanisms of LMLs. Rainfall was identified as the primary trigger of LMLs. Furthermore, the dynamic responses, deformation behavior, and failure characteristics of slope volumetric water content, pore pressure, and soil pressure under various geological factors were quantitatively analyzed, and the regulatory role of these factors in the evolution of slope micro-topography was clarified. Finally, by integrating field investigation results and analysis of regional geological evolution processes, the formation mechanisms of LMLs within the SCLP fault zone were elucidated, and a systematic framework for the evolution of failure modes under fault activity was proposed.

The geomorphologic and environmental evolution of the Loess Plateau is greatly affected by the strong fault activity, leading to the frequent occurrence of geological hazards, particularly the loess-mudstone landslide (LML). Thus, it is crucial to investigate the formation mechanism of such landslides in active fault zones. In this study, a field survey was conducted in the Weibei tableland of Baoji where the active fault zone is developed. To study the creep behavior of LML sliding zone soil, the triaxial creep tests of multi-stage loading under different water content, confining pressure, dry density, loess-mudstone binary structure (LMBS) contact surface angle, and thickness were carried out using the sliding zone soil samples (loess, mudstone, and LMBS samples) obtained from Wolongsi landslide in the study area as an example. Experimental results revealed that: (1) Water content has a significant weakening effect on the strength of LML sliding zone soil. The strength of the LMBS sample is extremely water-sensitive. The weakening effect of water on the long-term strength of LML sliding zone soil mainly manifested in promoting the elastoplastic deformation of loess and the viscoplastic deformation of mudstone. (2) The long-term strength of the LML slip zone soil increases linearly with the increase in confining pressure and increases exponentially with the dry density. (3) The degrading effect of the stratigraphic interface dip angle on the long-term slope strength is mainly reflected in the change in the weakening degree of water on the strength of the LML sliding zone. In addition, according to the test results, the traditional Nishihara model is improved by introducing nonlinear parameters, and a new constitutive equation describing LML sliding zone soil is established. The new constitutive model can accurately describe the creep curve's whole process especially sensitively identifying the accelerated creep stage. Finally, after conducting a field investigation and laboratory tests, the main hazard factors affecting the occurrence of the LML were analyzed in the presence of fault activity on the Weibei Plateau of Baoji, China, and its formation mechanism was revealed as well.

Loess has poor engineering geological properties due to its loose and porous soil structure. To meet the engineering requirements of bearing capacity of foundations in loess areas, various stabilizers have been added to the loess during construction. Currently, cement, fly ash, fibers (natural and synthetic) and ionic curing agents have been widely used as stabilizers worldwide. In this study, the Composite Improvement Method (CIM) was used to improve the loess mechanical properties. A series of experimental tests with three factors and five-level orthogonal were conducted on loess samples with the inclusion of cement, curing agent and polypropylene fiber, to investigate the relative strength in terms of direct shear tests and unconfined compression tests. The test results were analyzed by range and variance analysis to quantify the significance of the improved materials, and the optimal improvement scheme was obtained. The results show that cement content has the greatest influence on shear strength, especially on unconfined compressive strength (UCS), followed by polypropylene fiber content and curing agent content. To reveal the internal mechanism of loess improvement by CIM, the quantitative microstructural information of the improved soil was extracted, and the microscopic geometric parameters such as apparent porosity and fractal dimension were calculated and analyzed as well. Based on the qualitative and quantitative analysis of microscopic images, it is observed that CIM increased the roundness of soil particles, decreased the total number of soil particles, and reduced the fractal dimension of particles and pores. Additionally, the composite improvement mechanism of CIM is further revealed. CIM can stimulate the activity of each other between the improved materials and work together to improve the engineering geological properties of the soil.

The mechanical properties of the slip zone soil play an important role in the evolution of the loess landslides. To further understand these characteristics, a series of ring shear tests was conducted on the slip zone soils obtained from Tianshuigou landslide, to investigate the influence of moisture content, dry density, shear rate and shear method on the mechanical characteristics of slip zone soils. The experimental results showed that: an increase in the moisture content of the slip zone loess causes a significant reduction in the residual strength. Specially, both the residual cohesion and residual internal friction angle show a deceasing tendency with moisture content. The change in the residual cohesion is more sensitive to the variation in moisture content. Additionally, a trend that strength increased with the increasing of dry density was observed, and the influence degree of dry density on the increased strength is more pronounced at low moisture contents. Thirdly, shear strength shows a negative relationship with shear rate when the shear rate ranges from 0.01 mm/min and 1 mm/min. When the shear rate increased up to 10 mm/min, a stepped shear band is developed and the strength increased. In addition, the strain-softening phenomenon was observed in the single-stage shear tests, which was not noticed in the multi-stage shear tests and pre-shear tests. The residual strength obtained in pre-shear test and multi-stage shear test is slightly greater than that in the single-stage shear test. The experimental results herein can provide an important basis for analyzing the evolution mechanism and prevention of loess landslides.

Construction of high-speed railway subgrade on loess soils in the Loess Plateau is risky because such soil is susceptible to differential settlements. Various soil-improvement methods have been used to enhance the mechanical properties of loess. Lime-ash soil and cement-lime soil are the most commonly used methods in the improvement of loess subgrade, while few studies have been found on loess subgrade improvement by using composite material consisting of traditional materials and new materials. A series of direct shear tests and unconfined compressive tests were conducted on the loess specimen with the addition of three kinds of composite materials: traditional material cement, new material polypropylene fiber and SCA-2 soil curing agent. The numerical simulation was conducted on loess subgrade in an actual engineering practice. The experimental results show that cement, polypropylene fiber and SCA-2 soil curing agent can effectively improve the shear strength and compressive strength of loess, and the influence degree is cement > fiber > curing agent. Additionally, based on the relative strength characteristics of the improved loess, an optimal improvement scheme for the composite-material-modified loess was obtained: 16% cement content + 0.5% fiber content + 4% curing agent content. The numerical simulation results revealed that the compressive strength index of the improved loess has a significant impact on the subgrade settlement, and the optimal improvement scheme obtained from comprehensive analysis can effectively improve the settlement of high-speed railway subgrade under vibration load.

为了探讨滑带土在不同含水量和剪切速率下剪切特性,对甘肃黑方台黄土进行了一系列环剪试验和微观结构试验,结果表明:1)在相同条件下,残余强度随着含水率的增加而减小,这与含水率升高使得土体内部的胶结物质部分溶解,从而降低了土颗粒的摩擦性质有关.2)在较低的法向应力下,剪切速率对残余强度的影响较小;在较高的法向应力下,剪切速率的增加加大了剪面处的扰动,使得剪切面由单一、光滑过渡为具有一定厚度的阶状剪切带,从而加大剪切阻力.3)较高的含水量可以提高黄土骨架颗粒的圆度,增加颗粒间的接触面积,也使黄土团聚体相互粘结,在-定程度上减少了团聚体之间的空隙,从而改变了黄土的剪切特性.本研究可为从含水量和剪切速率对黄土残余强度影响的角度解释黄土滑坡的运动机理提供参考.

The primary fractures in rocks have an important influence on the rock breaking efficiency. In order to understand the fracture mechanism of broken soft rock strata more deeply, this paper carried out a series of discrete element particle flow numerical simulations with different prefabricated fractures (different number of fractures and fracture angles) based on laboratory rock mechanics tests. The results show that: the overall failure of rock mass is mainly tensile and compressive failure. And, when the crack reaches a certain depth, the influence of primary cracks in rock mass on rock breaking effect will be significantly weakened. Furthermore, in the process of rock breaking, the rock mass basically shows brittle fracture, and the crack initiation stress of rock mass has a good positive correlation with the degree of rock fragmentation. The crack initiation location is often accompanied by stress concentration, which is the key to rock fragmentation. And, the angle of prefabricated cracks will affect the crack initiation position. When the prefabricated crack angle approaches the top angle of the drill, the crack initiation stress will increase. Finally, the fracture mode and initiation mechanism of rock mass are revealed in the process of rock breaking. This study can provide some reference for the optimization of drilling parameters.

Loess landslides are closely related to the variation in mechanical properties of soils due to the leaching of irrigation water in the irrigation area which causes the loss of soluble salt in the loess stratum. To investigate the effect of leaching on the mechanical characteristics of loess, ring shear tests were conducted on the slip zone soil samples obtained from a typical loess landslide under different soaking time and salt concentration. Furthermore, the microstructural observations were made on shear planes by using SEM (scanning electron microscopy) tests. The experiment revealed that: firstly, the shear strength of loess decreases with the increase of soaking time before reaching the minimum value at the soaking time of 1 d, and then increases with the soaking time until reaching a relatively stable value. Secondly, the shear strength of loess has an increasing tendency with the salt concentration before reaching a maximum value at the salt concentration of 8%, and then shear strength decreases. In addition, a "stress-softening" was found for the loess samples with the soaking time of 1 d and salt concentration of 8%. It is found that the total number of micropores and small-pores in loess samples decreases with increasing salt concentration up to 8%, but increases rapidly between salt contents of 8% and 20%. The SEM tests showed that the increase in salt concentration (0% to 8%) facilities the formation of small aggregates within loess soils, which in turn promotes the increasing of shear strength. However, further increase in salt concentration (8% to 20%) helps the development of relatively large aggregates in loess samples, resulting in the reduction in shear strength.