Loess slopes are susceptible to rainfall due to the water sensitivity and collapsibility of loess. The aim of this study is to investigate the instability mode, failure mechanism and control effect of homogeneous loess landslide under rainfall by using physical model experiments and numerical simulation, combined with a new anchor cable with negative Poisson ratio (NPR) structural effect. The findings indicated that the loess slope's failure under heavy rainfall is characterized by progressive shallow flow-slip instability, encompassing three deformation modes and seven deformation characteristics. Water content, pore water pressure and earth pressure monitoring instruments capture the dynamic response of internal hydromechanical properties within the loess slope during intermittent heavy rainfall, clarifying its failure mechanism. Rainfall leads to soil softening and a reduction in strength. The effective stress of shallow soil and potential sliding surfaces diminishes due to decreased matrix suction and increased pore water pressure. The accumulation of internal and external deformation eventually leads to the disintegration of the shallow layer of the loess slope. Numerical simulation results indicated that rainfall significantly affects the shallow layer of the loess slope, with greater subsidence deformation observed at the slope's crest. Indoor and field monitoring findings revealed the pattern of Newton force on the loess slope in response to rainfall and demonstrated its seasonal dynamics, characterized by an increase during the thaw-collapse and flood periods, followed by a decrease in the frost-heave period.

Shallow slope failures occur frequently in the Loess Plateau region and the ecological materials are usually used for slope protection. The mechanical characteristics and strength models of the interface between environmental protection materials and native materials are crucial for evaluating the effectiveness of slope protection. In this study, the polypropylene fiber and guar gum are used for slope protection, and indoor experiments are conducted to elucidate the mechanical performance changes at the interface between untreated loess (UL) and guar gum-treated fiber-reinforcement loess (GFL) under different moisture content and curing time. A damage strength model of the interface between untreated loess and guar gum-treated fiber-reinforcement loess (UL-GFL) is constructed based on statistical damage theory. The results show that guar gum can aggregate and cement loess particles, while polypropylene fiber enhances the friction between loess particle aggregates. The synergistic effect of these two materials significantly improves the strength and hydraulic characteristics of loess. The cohesion and internal friction angle of the interface between untreated loess and guar gum-treated fiber-reinforcement loess decrease with an increase in moisture content and increase with an extended curing time, stabilizing when the curing time exceeds 7 days. The strength model for the interface of untreated loess and guar gum-treated fiber-reinforcement loess is established. The proposed model is verified through experimental data based on the stress-displacement relationship. The findings of this research can provide an important reference for the application of ecological protection materials on loess slopes.

In order to investigate the impact of plant root systems on the stability of loess shallow slope, this study conducted plant morphology investigations and direct soil shear tests to analyse the morphological characteristics of alfalfa and the shear characteristics of alfalfa root-loess composites under different soil bulk densities and soil moisture saturation levels. Additionally, the reinforcing effect of the alfalfa root system on the reliability of loess slopes was assessed using the Monte Carlo method. Slope reliability analysis refers to the estimation of the probability of slope failure under specific conditions. The results showed that plant weight and root weight both decreased following an exponential function with increasing soil bulk density. Root weight had a positively linear correlation with plant weight. The cohesion and internal friction angle of both loess samples without roots and with roots increased with increasing soil bulk density. The cohesion and internal friction angle of the two kinds of samples could decreased at less and more than 30% soil moisture saturation. The cohesion and internal friction angle of the root-soil composites were significantly higher than those of the rootless soil. The decrease of soil bulk density and the increase of soil moisture could increase the difference of the two mechanical parameters between the two kinds of samples. Assuming the thickness of the landslide body was 0.3 m, the failure probability of loess slopes covered with alfalfa significantly decreased from 34.97 to 14.51% compared to slopes without vegetation cover. Alfalfa roots significantly increased the reliability of the loess slopes in stability.

The long-term safety and durability of anchor systems are the focus of slope maintenance management and sustainable operation. This study presents the observed temperature, humidity, and anchor bolt stress at varying depths from four-year remote real-time monitoring of the selected loess highway cut-slope. The potential correlation between slope hydrothermal environment and anchor stress is analyzed. The anchor serviceability and durability were evaluated by establishing a time-dependent mathematical model of axial forces. The results show that the slope shallow loess exhibited hydro-thermal fluctuations annually during operation, subjecting the loess to continuous dry-wet cycles. Soil elastic deformation induces anchor axial force fluctuations due to hydro-thermo effects, while damage creep leads to the annual increase in axial force peaks and valleys. The increase in axial force is more significant at the upper slope and lower slope, thereby increasing the risk of retrogressive landslides in loess slopes. The time-dependent model of anchor axial force composing negative exponential and sine functions was proposed. The cyclic amplitudes, lower limits, and periods of temperature and humidity in slope can determine the model coefficients. The development patterns of axial force are classified into stable type, slow growth type, and accelerated growth type according to the characteristics of the model coefficients. Predicted results indicate that the anchor axial forces are lower than the landslide threshold within 30 years of slope operation, ensuring long safety and serviceability. Results provide a reference for the long-term safety evaluation and formulation of maintenance plans for loess slopes reinforced by anchor systems.

BackgroundIn the Loess Plateau region, significant engineering activities have led to many exposed loess slopes. These slopes have undergone a series of shallow failures under rainfall, significantly affecting their stability. Vegetation can somewhat restore the ecological damage to the slope surfaces and enhance their stability. Thus, studying the spatiotemporal evolution of soil moisture migration under vegetation protection on loess slopes is crucial.MethodsEmploying experimental designs with slope gradients of 45 degrees and 60 degrees, this investigation is structured around a trio of core objectives: to delineate the processes of rainfall infiltration and its redistribution within the slope, to chart the evolution of soil water within the loess soil matrix, and to discern the impacts of slope inclination on soil water dynamics. Critical to this study are the monitoring of volumetric moisture content, matric suction, and the external variables of rainfall and temperature, alongside an analysis of soil water potential and moisture movement as observed in laboratory setups and simulated through Hydrus-2D.ResultsThe study revealed that slope angle significantly affects soil moisture infiltration and redistribution. The steeper slope (60 degrees) exhibited more pronounced fluctuations in soil water potential, particularly during the rainy season, reflecting the dynamic nature of water movement. This slope also demonstrated sharper transitions in soil moisture during drying periods, indicating a greater sensitivity to weather changes. Water movement parallel to the slope surface was faster on steeper slopes, especially under drying conditions, with more pronounced lateral downslope flow at the surface layer. In contrast, the gentler slope (45 degrees) showed more consistent moisture retention during wet periods, with slower and more uniform soil moisture movement, leading to a steadier moisture gradient and prolonged upslope movement. Vegetation plays a crucial role in modulating soil moisture dynamics, with grass growth being more effective on the steeper 60 degrees slope. The extensive root network on this slope enhanced water retention, increased soil permeability, and reduced erosion. During the drying phase, deeper root systems significantly reduced volumetric water content at shallower depths, promoting higher moisture content in the middle sections of the slope.

Geological disasters occur frequently in the Loess Plateau due to the joint fissures in the strata and human engineering activities. Against this background, the deformation and failure mode of the loess slope with the structural plane under excavation and the extension mechanism of the structural plane are analyzed and summarized. The results showed that: (1) Through the physical model test, the deformation failure mode of the slope is summarized as the tension-splitting, pressure-sliding shallow failure. The collapse failure process is defined as four stages: Compression deformation, creep deformation, slip deformation and slip failure. (2) Slope displacement is concentrated beneath the pressure plate, increasing linearly under load conditions but becoming nonlinear after excavation conditions. As the excavation angle rises, the displacement range along the structural plane gradually extends toward the slope toe. The displacement time-history curve shows three stages: The lifting load stage, the cumulating deformation stage, and the sliding failure stage. (3) The stress redistribution caused by excavation, prompting deformation and potential failure. As internal stress nears the soil strength limit, human-induced disturbances exacerbate stress redistribution, leading to accumulated stress. Finally released through deformation and cracking. Each excavation condition modifies the original loading transfer path, driving stress redistribution at the slope surface and at the structural plane's tip. (4) The sudden drop in stress level and sudden rise of accumulated settlement are the characteristics of slope sliding failure. The position of the structural plane determines the position of the slope sliding surface. (5) According to the external characterization of the structural plane, the extension process of the structural plane can be defined as four stages: Initiation of crack extension, classification deformation, sub extension and compression sealing. According to the extension of the structural plane, the spreading cracks of the slope's internal structural plane are defined as two types: Fractured cracks and shear cracks.

Heavy rainfall is the main factor inducing the failure of loess slopes. However, the failure mechanism and mode of terraced loess slopes under heavy rainfall have not been well investigated and understood. This paper presents the experimental study on the deformation and failure of terraced loess slopes with different gradients under extreme rainfall conditions. The deformation and failure processes of the slope and the migration of the wetting front within the slope during rainfall were captured by the digital cameras installed on the top and side of the test box. In addition, the mechanical and hydrological responses of the slope, including earth pressure, water content, pore water pressure, and matric suction, were monitored and analyzed under rainfall infiltration and erosion. The experimental study shows that the deformation and failure of terraced loess slopes under heavy rainfall conditions exhibit the characteristic of progressive erosion damage. In general, the steeper the slope, the more severe the deformation and failure, and the shorter the time required for erosion failure. The data obtained from sensors embedded in the slope can reflect the mechanical and hydraulic characteristics of the slope in response to rainfall. The earth pressure and pore water pressure in the slope exhibit a fluctuating pattern with continued rainfall. The failure mode of terraced loess slopes under extreme rainfall can be summarized into five stages: erosion of slope surface and formation of small gullies and cracks, expansion of gullies and cracks along the slope surface, widening and deepening of gullies, local collapse and flow-slip of the slope, and large-scale collapse of the slope. The findings can provide preliminary data references for researchers to better understand the failure characteristics of terraced loess slopes under extreme rainfall and to further validate the results of numerical simulations and analytical solutions.

The understanding of the dynamic behavior characteristics and mechanisms of seismic landslides in seasonal frozen soil areas following severe freeze-thaw damage is currently limited. Taking a compacted loess slope in Lanzhou National New Area of China as the prototype, freeze-thaw cycle tests and large-scale shaking table tests were conducted, and the dynamic responses of freeze-thaw slope and non-freeze-thaw slope under different amplitudes, directions, and intensities of seismic waves were compared and analyzed. The results indicate that the acceleration responses of compacted loess slopes increase with the increase of the slope height and the value of the slope shoulder is the largest. The acceleration responses also increase with higher seismic intensity. On the other hand, earth pressure responses decrease as the slope height increases, but initially increase with higher seismic strength before eventually decreasing prior to slope failure. Comparatively, the acceleration responses of the freeze-thaw slope are stronger than those of the non-freeze-thaw slope, while the earth pressure responses are smaller, particularly in frost-heaving zones The compacted loess slope demonstrates good stability under seismic waves. However, the loosed and wetted surface after freeze-thaw cycles may experience abrupt shear slip during high-intensity seismic waves. These findings hold significance for stability analysis and reinforcement strategies for engineering slopes in the Loess Plateau with seasonal freezing and thawing.

A profound understanding of the interaction between loess slopes and tunnels, along with the mastery of protective measures for tunnels crossing loess slopes, is crucial for ensuring the excavation and operation safety of tunnels in loess slope areas. This article summarizes research findings on the loess slope-tunnel system, concentrating on sources triggering failures, the acting mechanism of failures, and strategies for failure mitigation. Loess slopes, serving as the tunnel's bearing medium, may suffer from engineering disturbances during construction and operation, significantly affecting their stability. This is reflected in the intensification of crack formation, water infiltration, and vibration propagation in the slope. The degree of slope-tunnel interaction depends on relative spatial positioning, slope characteristics, and construction parameters. Although extensive research has focused on tunnel deformation in orthogonal systems, oblique systems require additional investigation. At different stages, preventing failure involves three levels: proactive avoidance, proactive mitigation, and passive reinforcement. Traditional approaches involve divide and conquer, but considering tunnels and slopes as an integrated whole is an emerging research area. Innovative technologies, like Negative Poisson's ratio anchor cables and Steel-Concrete Composite Support for challenging loess terrains, are introduced. Applying these technologies in practical engineering is recommended to accumulate experience and support their mature application. This review can offer valuable support for designing, operating, and managing tunnels crossing areas prone to loess landslides.

In loess slopes, landslides are easily caused by rainfall and can be prevented by using retaining structures of stabilizing piles. This paper investigated the deformation and mechanical behaviors of the cantilever and fully buried stabilizing piles under complex pile-soil interactions. The deformation and mechanical behaviors, failure modes, and soil pressure distributions of two types of stabilizing piles were analyzed based on field model tests. Further, a calculation method for stabilizing piles considering nonlinear pile-soil interactions was proposed. Also, the numerical solution of the pile deformation and force was obtained by using the finite difference method and Newton's iterative method. The results showed that the deformation and mechanical behaviors of fully buried piles are superior to those of cantilever piles. Fully buried piles and cantilever piles have plastic double-hinged and single-hinged failure modes and undergo bending damage and shear damage, respectively. Besides, the landslide thrusts and soil resistances acting on the pile showed a parabolic distribution pattern. Compared to the model test results, the traditional calculation method overestimated the deformation and internal force of the stabilizing pile by 37.32%, and the newly proposed calculation model considering nonlinear pile-soil interactions was more consistent with the measured values. The study results help to guide the design and calculation of stabilizing piles under complex pile-soil interactions.