Soil Landslides Research Articles

Stability Analysis of Expansive Soil Slope Considering Seepage Softening and Moistening Expansion Deformation

Expansive soil is a kind of clay soil that expands rapidly after being immersed in water and shrinks significantly after losing water. The expansive soil slopes exposed to the atmosphere are in the process of continuous dry and wet cycles and are extremely unstable under the conditions of rainfall. Based on saturated-unsaturated seepage theory, the unsaturated seepage process and humidification process of the expansive soil slope under rainfall were simulated, and a related FORTRAN language program was developed. The effects of matrix suction changes, seepage softening, and moistening expansion during the seepage process were considered. The effects of strength attenuation, seepage softening, and moistening expansion on the overall stability of the expansive soil slope were analyzed. The results show that under the action of rainfall, the failure mode of the expansive soil slope after multiple dry-wet cycles is shallow collapse, and the failure surface is located in the weathered area, which is quite different from the traction landslide of the homogeneous expansive soil slope. After considering the moistening expansion and softening effects, the maximum displacement of the slope increased by an order of magnitude, and the safety factor decreased significantly. The significant increase in the horizontal stress of the lower half slope is the main reason for the landslide. The research results well explain the special tractive and shallow properties of typical expansive soil landslides.

Decreasing Landslide Erosion on Steeper Slopes in Soil‐Mantled Landscapes

AbstractSlope‐stability models predict that steeper hillslopes require smaller hydrological triggers for shallow landslides to occur due to the added downslope pull of gravity, which should result in more frequent landslides and faster erosion. However, field observations indicate that landslide frequency does not consistently increase on steeper hillslopes. Here, we use measurements of 1,096 soil landslides in California and Switzerland, and a compilation of landslide geometries, to show that steeper hillslopes typically have thinner soils and that thin soils inhibit landslides due to enhanced roles of cohesion and boundary stresses. We find that the landscape‐averaged landslide erosion depth peaks near the threshold slope for instability, and it drops to half that value on hillslopes that are just 5° to 10° steeper. We propose that faster rates of soil creep on steeper slopes cause thin and more stable soils, which in turn reduces landslide erosion, despite the added pull of gravity.

Landslide characteristics in the Loess Plateau, northern China

Landslides play an important role in landscape evolution of the Loess Plateau, northern China, but they have not been systematically analysed across the region. The contribution to regional rates of erosion and sediment budgets is poorly known as a consequence. Co-seismic landslides are a significant natural hazard, and exacerbate the threat posed by active faults in the region, but this aspect of the landslides is also poorly quantified. This paper presents inventories for ~80,000 landslides in the Loess Plateau, and analyses the distributions and extents. Four study areas focus on the epicentres of major (M > 7) historical earthquakes, from 1303 CE (Hongdong), 1556 (Huaxian), 1718 (Tongwei) and 1920 (Haiyuan), which are likely to have been major triggers for landslides in these regions. A fifth study area focuses on landslides in the aftermath of localised storms in 2010 in the Tianshui region, to allow comparison of landslides clearly triggered by rainfall with landslides in the regional inventories. Landslides predominantly resulted from failure of the regional loess blanket that gives the region its name, or the soil profile developed above it. Rainfall-generated landslides are dominantly surficial soil landslides. Landslides preserved in the four epicentral areas are larger and deeper, and resemble global bedrock landslides in the dimensions. Total volume of landslide in each of the four epicentral areas are on the order of 3–7 km3; these volumes are likely to be the cumulative totals of repeated earthquakes in the same regions, with each event reactivating landslide scarps on hillsides. Comparison of landslide distributions and modern settlement patterns suggests that future M > 7 earthquakes striking the Loess Plateau may trigger landslides that could directly hit 30–50% of the communities.

Study on the Hydraulic Parameters of Woshaxi Landslide Soils during Water Level Drawdown of Three Gorges Reservoir

Variation of hydraulic parameters for unsaturated soil in bank slopes during reservoir water rising or falling process is crucial to scientific analysis and evaluation of bank slope stability. In this paper, soil samples from the Woshaxi landslide in the Three Gorges Reservoir were taken for a permeability test under reservoir drawdown conditions using an independently developed apparatus, which can simulate the variation process of internal seepage in bank slope soils. Changes of particle gradations, soil-water characteristic curves, and unsaturated permeability functions of the soil samples during reservoir falling process were studied by combining with the physical empirical model and numerical simulation. Permeability test results show that fine particles in soil samples migrated and were lost under seepage force action during the tests, leading to a continuous decrease of fine particle content indicated in the grain size distribution curves, in which particles with a size less than 0.02 mm lose the most. As permeation time increases, the soil saturated permeability enhances constantly with the change rate increasing first and then decreasing. The soil-water characteristic curves change obviously in the high matrix suction section (10~104 kPa), and the volumetric water content decreases constantly and shows a positive correlation with the fine particle content. During the permeability test, the unsaturated permeability coefficient corresponding to a fixed matric suction increases with the drawdowns of the reservoir water level. Slope stability results show that neglecting the variational characteristics of hydraulic parameters in slope stability evaluation can result in a bigger safety factor, which is dangerous for slope safety evaluation. The research results can provide a scientific basis for the stability analysis and evaluation of the bank slopes in the Three Gorges Reservoir Area.

Study on the Mechanical Characteristic of Micropiles Supporting Landslide Under Step-Loadings

To study the reinforcement effect and the mechanical characteristic of micropiles in supporting soil landslide under step-loadings, two soil landslide models were built: the reinforced landslide with three rows of micropiles and the unreinforced landslide. The mechanical characteristics and failure mode of micropiles under step-loadings were analyzed by monitoring the displacement of landslides and pile-tops, and the strain of micropiles. The results indicate that the bearing capacity of the reinforced landslide with micropiles is increased by three times compared to the unreinforced landslide. Micropile plays a major role in anti-bending and shear-resistance. The failure pattern of micropiles shows reverse “S”-type. The destruction area of the back pile and the middle pile mainly distributes in the area that 1.7–3.1 times pile diameter above the sliding surface and the area that 1.7–2.9 times pile diameter below the sliding surface. The destruction area of the front pile mainly distributes in the area that 2.6–4.3 times pile diameter above the sliding surface and 1.7–2.9 times pile diameter below the sliding surface, and destructiveness of the front pile is less than that of the other two rows of piles. Before the landslide enters the unstable status, the bending moments of different rows of piles have not much difference. However, when the landslide is at the completely failure state, the back pile and the middle pile play more important role than the front pile.

Forecasting Disastrous Characteristics of Highway Landslides Using the Material Point Method: A Surcharge‐Induced Perspective

Precisely forecasting the disastrous characteristics of landslides can address the optimized preliminary design of the highway landslide stabilization. In this paper, taking the surcharge‐induced landslides as an example, we developed the models of the material point method (MPM), a novel meshless numerical method, to calculate the large deformation of the highway landslides, with the affordable computing power. After convincing verification of the MPM model to simulate a surcharge‐induced soil landslide, 32 typical postfailure scenarios were analyzed to obtain the highway landslide run‐out processes and disastrous characteristics, such as the sliding distance and speed of the leading edge and sliding body morphology. Moreover, linear regression equations of the maximal sliding distance and speed were deduced after verification, to forecast the reasonable avoiding distance. The maximal sliding distance and speed were found to be negatively linearly correlated with the internal frictional angle and cohesion of the soil, and positively linearly correlated with the surcharge and the slope angle, respectively. Optimized preliminary design, of the highways in the mountainous and hilly areas, can be performed based on those insights.

Landslide Failure Mechanisms of Dispersive Soil Slopes in Seasonally Frozen Regions

Hydraulic projects with dispersive soil in seasonally frozen regions are susceptible to landslide failures. The mechanism of such landslide failures has not been fully understood thus far; therefore, it was investigated in this study by using on‐site surveys, laboratory tests, and theoretical calculations. The results showed that the landslides of dispersive soil in seasonally frozen regions could be categorized as shallow‐seated landslides and deep‐seated landslides. The preconditions for landslide occurrence were soil mass looseness and cracks, caused by freeze‐thawing. The degradation of dispersive soil led to a rapid influx of water into the soil. The reason for shallow‐seated landslides was that the numerous sodium ions present in the soil mass dissolved in water and damaged the soil structure, resulting in a substantial reduction in shear strength. The reason for deep‐seated landslides, however, was the erosion due to rainfall infiltration after the shallow‐seated landslides caused tensile cracks at the top of the slope, leading to soil instability. Landslide failures occurred when the dispersing soil slope underwent freeze‐thawing and saturated soaking. The sliding surface was initiated at the top of the slope and gradually progressed to the bottom along the interface between the soil layers.

Evaluation and remediation of post-wildfire slope stability

Catastrophic mudflows and landslides triggered by rainfall can occur suddenly and move with high speed, damaging electrical and civil infrastructure and threatening human and wildlife. Due to the climate change and extreme weather increase, it is likely that wildfires and consequently mudflows will increase in frequency in the future. The risk of mudflows and landslides increases in post-wildfire areas mainly because of water repellent soil which forms on slopes. Water repellency, or hydrophobicity, can occur due to the burning of the accumulated organic matter in soil. Hydrophobicity repels water and prevents infiltration of water into the soil, which results in soil erosion, mudflows and landslides. In this study, a series of experimental laboratory tests are conducted on regular, hydrophobic and Xanthan gum-treated hydrophobic sand. Xanthan gum, which is an environmentally friendly biopolymer, can be substituted for chemical material used for soil improvement and decrease the CO2 emissions and enhance environmental slope protection. Xanthan gum can enhance the inter-particle cohesion and can hold a large amount of water and consequently help the recovery of the vegetation. Contact angle, direct shear and rain simulation tests are conducted on samples. Results show that in Xanthan gum treated slope the rate of erosion and the risk of mudflow decreases. It is also observed that the Xanthan gum treated sample can retain more water and consequently decreases the rate of wind erosion and helps the dust-control in burned areas.

Model test of the influence of cyclic water level fluctuations on a landslide

Many landslides in reservoir areas continuously deform under cyclic water level fluctuations due to reservoir operations. In this paper, a landslide model, developed for a typical colluvial landslide in the Three Gorges Reservoir area, is used to study the effect of cyclic water level fluctuations on the landslide. Five cyclic water level fluctuations were implemented in the test, and the fluctuation rate in the last two fluctuations doubled over the first three fluctuations. The pore water pressure and lateral landslide profiles were obtained during the test. A measurement of the landslide soil loss was proposed to quantitatively evaluate the influence of water level fluctuations. The test results show that the first water level rising is most negative to the landslide among the five cycles. The fourth drawdown with a higher drawdown rate caused further large landslide deformation. An increase of the water level drawdown rate is much more unfavorable to the landslide than an increase of the water level rising rate. In addition, the landslide was found to have an adaptive ability to resist subsequent water level fluctuations after undergoing large deformation during a water level fluctuation. The landslide deformation and observations in the field were found to support the test results well.

Analysis of Wet Soil Granular Flow down Inclined Chutes Using Discrete Element Method

This paper presents numerical simulation and analysis of two numerical experiments of wet soil granular flow down inclined chutes based on the JKR(Johnson-Kendall-Roberts)-cohesion model of the discrete element method. JKR is a cohesive contact model, which can reflect the influence of van der Waals forces in the contact range to simulate cohesive granular matter. A surface energy coefficient kw was proposed to reflect the liquid surface tension between particles, and maximum surface energy (γmax) of wet soil composed of uniform particles was obtained at 0.2 J/m2. Computational results show that surface energy (γ) and granular size play significant roles in the simulation of wet soil granular flow. The larger surface energy is, and the stronger of adhesion between soil grains. Besides, surface energy also has a great effect on the average velocity and kinetic energy of the moist soil avalanches. With baffles on both sides of the inclined chute, the dry soil granular flow has the longest runout distance on the horizontal plane; with the increase of surface energy, the runout distance decreased gradually. However, without baffles on both sides of the geometric model, the runout distance of wet soil granular flow is farther, though expansion to the sides is more obvious. Wet soil with larger grains requires larger surface energy to maintain the soil structure intact during the sliding process. Furthermore, with the increase of granular size, the soil structure is not compact enough, and the cohesion between water and soil grains is extremely poor, which lead to the impact scope expanded of wet soil landslide disasters.

Slip surface identification based on engineering properties analysis of weathering breccia at landslide occured in mount pawinihan, central java, indonesia

Landslide mitigation may be performed in various methods, such as by identifying the weathering degree in order to determine the position of slip surface. Slip surface is imaginary plane beneath surface dividing the moving part of slope mass with the rest, In short, it may also be defined as the weakest zone where the landslide may occur. Therefore, slip surface is the main object of this research which result may be used as a reference for further mitigation step. This research is conducted in the landslide case of Mount Pawinihan, Banjarnegara. The research is conducted by identifying the weathering degree of heterogenic material based on the British Standard EN ISO 14689-1. Engineering properties sampling was conducted after identification of weathering zone and use systematic sampling base on zone of weathering. The research result shows that the landslide soil mass under study may be divided into four weathering zones exposing on surface, while the position of slip surface may be identified in the weathering zone 3 (moderately weathered). This zone is a boundary of rock and soil condition.

Research on fibre Bragg grating monitoring in the gravel soil landslide experiment

Fibre Bragg Grating (FBG) sensor is a new sensor with numerous advantages. How to apply in the safety monitoring of landslide engineering is still in experiment and research stage. Here, FBG is used to monitor the landslide process of the gravel soil pile. Before monitoring experiment, the article first tests FBG packaging and burying effect by two tests in lab, one is sand pile landslide test which proves vertical buried is feasible and the other is loading test on the steel bar sensor which proves the wavelength change of FBG on steel bar sensor has a good linear relationship with the loading change. Then, buried the steel bar sensor in the gravel soil slope after simple encapsulation. Stress and strain monitoring results of grating sensors are obtained in landslide which is formed through the simulation of excavation construction. The experimental data show that through correct embedding FBG sensors can effectively monitor the stress–strain change of the slope. FBG provides a new way for the landslide early warning.

Forecasting Groundwater Level for Soil Landslide Based on a Dynamic Model and Landslide Evolution Pattern

The occurrence and migration of groundwater is a key natural factor that directly affects the stability of landslides, and rainfall has a large effect on the groundwater level in soil landslides. This study used the Baijiabao landslide in the Three Georges area of China as the research subject and used a combination of more than seven years of rainfall and GPS (Global Positioning System) monitoring data from 2007 to 2013. We applied the K-means clustering method to classify one cycle of the evolution stage into three classes based on the relative displacement of the main sliding surface of the landslide. To illustrate the relationship between the three landslide evolution divisions and the dynamic indicators, we identified rainfall factors that correspond to the actual change in the landslide using the minimal description length principle method. Based on the relationship between the actual deformation stage of the landslide and the rainfall factor from historical monitoring, the mean absolute error of the dynamic exponential smoothing model was 0.053, and the correlation coefficient was 0.929. The size of the smoothness index could be modified in real-time to achieve dynamic correction, which indicates that the model exhibited high reliability and confirmed the usefulness of the proposed model for forecasting groundwater level changes based on deep-seated soil landslide type.

Field model experiments to determine mechanisms of rainstorm-induced shallow landslides in the Feiyunjiang River basin, China

This paper investigates rainfall infiltration processes and the failure mechanisms of slopes in the Feiyunjiang River basin. Field model experiments were conducted on a selected residual soil slope next to the Fuao landslide, which was about 30 m long and 25 m wide, and failed along the interface between soil and bedrock during typhoon Megi. The results indicated that rainfall infiltration over the slope surface had little impact on pore water pressure and deformation of the slope, while the coupled action of slope surface infiltration and preferential infiltration through an artificial ditch at the back of the slope caused rapid saturation near the interface between the residual soil and bedrock, resulting in significant displacement along the interface. Other preferential infiltration channels on slopes in the Feiyunjiang River basin include tension cracks, water impoundment and intrusive dykes and their weathered layers. The conclusions derived from this study are helpful in understanding rainstorm-induced soil landslides in the Feiyunjiang River basin in China, and possibly in other similar slope settings under comparable climate conditions.

Experimental investigation on progressive deformation of soil slope using acoustic emission monitoring

The deformation process of soil slopes observed during a landslide can have progressive characteristics, which can be quantified through acoustic emission (AE) monitoring. A model test is designed based on the geological model of a translational landslide, and experiments are conducted to reproduce the three-stage deformation process of a soil slope. The deformation process of progressive landslides is described using equations, and an entire loading process is realized using a programmable logic controller (PLC). The maximum velocity of a sliding body is measured to be approximately 6 mm/s with the final displacement exceeding 210 mm. The AE, deformation, and mechanical measurements of the entire process are compared to comprehensively evaluate the evolution behavior of progressive soil landslides. The experiments demonstrate that AE rates can linearly quantify slope velocity as well as help quantify slope acceleration. A copper tube and an aluminum tube are compared as different waveguides, and the quantitative relationship between the AE and deformation obtained by the active copper waveguide is found to be more distinct. The experiments also show that the acceleration of a slope can be effectively used as a discriminant index of progressive landslides, which has the potential to be applied in field monitoring.

Variability of permeability and seepage characteristics in soil landslides: a test case in the Three Gorges Reservoir Area, China

Abstract This study presents assessments of the spatial variability of a soil landslide in the Three Gorges Reservoir Area in China. The results challenge the idea that variability of permeability within a landslide is secondary. Consequently, it cannot be assessed through single representative values. It was found that its variability spans two orders of magnitude, a consequence of it being influenced by both morphology and regolith properties. Identification of zones that display comparable behavior can be done through assessment of remote-sensing images collected by drones, as growth patterns of vegetation correspond well with zones that displayed similar permeability coefficients within the landslide body. Furthermore, extensive variability of permeability was caused by a diverse range of seepage mechanisms, namely pipe network flow, interface network seepage and pore water seepage. Thus, the hydraulic behavior of large landslide bodies is remarkably complex.

Comparative Study on Calculation Methods for Stability Evaluation Based on BIM Models of Soil Landslides

The purpose of landslide prevention and control is to keep the stability within a safe range. This paper proposes a new direction of landslide information prevention and control with BIM technology for soil landslide, which is a typical type of landslide. The BIM model was established by referring to the engineering geological parameters of typical soil landslides, and then several commonly used landslide stability calculations were compared and studied by using the model research method. On the basis of BIM model of typical soil landslide, the results of calculating related engineering geological problems by different stability calculation methods were verified, and the characteristics of different stability calculation methods were revealed. When several common methods were used to calculate the stability of typical soil landslides. How to select the appropriate methods for calculations is an inevitable problem whenever the stability evaluation of landslide prevention and control is carried out, so it is of important engineering value and significance for this research.

Effects of layering on triggering mechanisms of rainfall-induced landslides in unsaturated pyroclastic granular soils

Rainfall-induced landslides are widespread in shallow layered granular soil deposits. In many cases, slope instability is related to the decrease of suction during rainwater infiltration. However, the contrasts in the unsaturated hydraulic properties of the soils deeply affect the infiltration process, thus influencing slope failure. Coarse-textured soil layers embedded between finer ones may initially confine the process within the overlying finer layers, delaying the infiltration and eventually inducing lateral flow diversion. Nonetheless, depending on the state variables at the beginning of rainfall as well as on rainfall characteristics, the coarser layers may or may not have a positive effect on stability. The results of research based on advanced geotechnical characterization, physical and numerical modeling, and field monitoring have been analyzed to investigate the effects of layering on slope stability.

Formation analysis and characteristic estimation of the debris flow disaster of Mengdong River, Malipo County on September 2nd, 2018

Based on the on-site investigation of debris flow disasters in Mengdong River Basin of Malipo County on September 2, 2018, the characteristics of disasters and their formation and evolution process are analyzed from the aspects of source, topography and water resources. Heavy rainfall is the inducement factor of this debris flow. The complex topographic and geomorphological features in the channel provide conditions for the evolution and scale-up of the debris flow: (1) hundreds of shallow soil landslides in the region provide sufficient material resources for the debris flow, enhance the hydrodynamic conditions of the debris flow and increase the amount of erosion along the way; (2) multiple bedrock entrapments and falls in the channel enlarged the debris flow. The scale and velocity of debris flow; (3) The volume weight of debris flow increases gradually with the supply of solid materials along the way. The study shows that precipitation is the fundamental cause of debris flow. The precipitation causes the initiation and overlap of landslide, slope and channel sources in the valley. From the development trend, the debris flow in the valley is in the stage of high frequency development, and the possibility of large-scale debris flow still exists. The possibility and frequency of occurrence will be greatly increased. High frequency and small and medium-sized debris flows will be the characteristics of debris flow activities in this gully in the future. It is necessary to control ditches in time and strengthen monitoring and early warning.

Typical characteristics of large-scale landslides in the transition belt between the Qinghai-Tibet Plateau and the Loess Plateau

The transition belt between the Qinghai-Tibet Plateau and the Loess Plateau is an area where geohazards occur frequently. To develop a basic understanding of the geohazards in this region, a detailed field investigation of large-scale landslides (i.e., > 106 m3 in volume) has been performed. The results show that 259 large-scale landslides have occurred in this region, of which 254 landslides are rock landslides and the others are soil landslides. These landslides have an average volume of 20.6 Mm3, are mainly concentrated along rivers, and have a linear density that reaches 0.45 landslides/km. Furthermore, more than 90% of the landslides are located within 5.0 km of a fault and more than 80% of the landslides are located at elevations of 1000–2600 m. With increasing landslide volume, the mobility increases, and approximately 45% of the landslides are sturzstrom-type landslides. Large-scale landslides are mainly concentrated along faults, especially around fault intersections. The typical failure mechanisms of the studied landslides are clearly influenced by the regional structure, earthquakes, and river incision.