Shallow Slope Failures Research Articles

Influence of the spatial variability of shear strength parameters on rainfall induced landslides: a case study of sandstone slope in Japan

Rainfall-induced landslides frequently occur in humid temperate regions worldwide. Research activity in understanding the mechanism of rainfall-induced landslides has recently focused on the probability of slope failure involving non-homogeneous soil profiles. This paper presents probabilistic analyses to assess the stability of unsaturated soil slope under rainfall. The influence of the spatial variability of shear strength parameters on the probability of rainfall-induced slope failure is conducted by means of a series of seepage and stability analyses of an infinite slope based on random fields. A case study of shallow failure located on sandstone slopes in Japan is used to verify the analysis framework. The results confirm that a probabilistic analysis can be efficiently used to qualify various locations of failure surface caused by spatial variability of soil shear strength for a shallow infinite slope failure due to rainfall.

Analysis of Rainfall-Induced Landslide on Unsaturated Soil Slopes

This paper investigates rainfall-induced landslides on partially saturated soil slopes using the 2011 Umyeonsan landslides at the center of Seoul, Korea. An integrated analysis of rainfall-induced landslide was carried out through laboratory tests, field tests, and numerical analysis. The results of comprehensive investigations in the Umyeonsan region demonstrate that landslide activity is closely related primarily to rainfall and soil properties and slope geometry, and vegetation. Numerical analysis was also performed to confirm the effect of these factors on landslide occurrence. Special attention was given to rainfall penetration analysis to determine the wetting band depth for shallow and deep-seated slope failure in watershed-scale landslide. The simulated results agree closely with the investigation results, which indicates that the applied method is appropriate for use in the simulation of landslides in unsaturated soils.

Key indicator tools for shallow slope failure assessment using soil chemical property signatures and soil colour variables.

Slope failure has become a major concern in Malaysia due to the rapid development and urbanisation in the country. It poses severe threats to any highway construction industry, residential areas, natural resources and tourism activities. The extent of damages that resulted from this catastrophe can be lessened if a long-term early warning system to predict landslide prone areas is implemented. Thus, this study aims to characterise the relationship between Oxisols properties and soil colour variables to be manipulated as key indicators to forecast shallow slope failure. The concentration of each soil property in slope soil was evaluated from two different localities that consist of 120 soil samples from stable and unstable slopes located along the North-South Highway (PLUS) and East-West Highway (LPT). Analysis of variance established highly significant difference (P<0.0001) between the locations, the total organic carbon (TOC), soil pH, cation exchange capacity (CEC), soil texture, soil chromaticity and all combinations of interactions. The overall CIELAB analysis leads to the conclusion that the CIELAB variables lightness L*, c* (Chroma) and h* (Hue) provide the most information about soil colour and other related soil properties. With regard to the relationship between colour variables and soil properties, the analysis detected that soil texture, organic carbon, iron oxide and aluminium concentration were the key factors that strongly correlate with soil colour variables at the studied area. Indicators that could be used to predict shallow slope failure were high value of L*(62), low values of c* (20) and h* (66), low concentration of iron (53mgkg-1) and aluminium oxide (37mgkg-1), low soil TOC (0.5%), low CEC (3.6cmol/kg), slightly acidic soil pH (4.9), high amount of sand fraction (68%) and low amount of clay fraction (20%).

Unsaturated hydro-mechanical behaviour of rainfall-induced mass remobilization in post-earthquake landslides

Clarifying the hydro-mechanical characteristics of the mechanism associated with mass remobilization is a major step towards landslide early warning, but this clarification is usually hampered by a lack of in situ evidence. In this study, shallow rainfall-triggered slope failures under partially saturated conditions were documented by combining instrumental evidence from field experiments on a natural co-seismic landslide and hydro-mechanical slope stability analysis in an earthquake-affected region. The results revealed the transient processes and unsaturated conditions associated with mass movement in response to rainfall, and preferential flow paths were found to dominate the hydrological processes during rainfall infiltration in the landslide deposit. The results also demonstrated the importance of certain hydrological parameters, including soil matric suction and moisture content, in landslide early warning. This study reveals a partially saturated hydro-mechanical behaviour to predict the initiation of rainfall-induced landslides during post-earthquake disaster relief.

Assessment of Guar Gum Biopolymer Treatment toward Mitigation of Desiccation Cracking on Slopes Built with Expansive Soils

Expansive soil embankments are prone to shallow slope failures caused by associated swell–shrink movements. Previous studies have confirmed that seasonal changes and corresponding volumetric changes are responsible for desiccation cracking, which is a major factor behind shallow slope failures of highway embankments. For the past few years, soil stabilization proved to be an effective way to mitigate the swell–shrink property of expansive clays. The current study addresses the feasibility of guar gum biopolymer in mitigating the swell–shrink behavior of clays and in turn making it possible to adopt them as stable geomaterials. The sustainable benefits of biopolymers far exceed the environmental benefits from conventional stabilizers that contractors typically use. This paper presents a comprehensive laboratory study, followed by finite difference modeling analysis, on biopolymeric guar gum–remediated expansive soils collected from shallow slope failure-prone areas. For this study, two dam locations, at Grapevine Lake and Joe Pool Lake, Texas, that were originally constructed with expansive soils, were considered. The engineering performance of biopolymer-treated soils was evaluated and an optimum dosage was recommended for mitigating desiccation cracking at the test sites. Slope stability analyses were conducted using Fast Lagrangian Analysis of Continua in Three Dimensions software by adopting laboratory-determined strength parameters to determine the range of the factor of safety for the slopes. The variation of the factor of safety computed with the inclusion of enhanced engineering parameters from guar gum treatments revealed the advantages of adopting this treatment.

Influence Factors Involving Rainfall-Induced Shallow Slope Failure: Numerical Study

Influence Factors Involving Rainfall-Induced Shallow Slope Failure: Numerical Study

Hydrological responses and stability analysis of shallow slopes with cohesionless soil subjected to continuous rainfall

Understanding the hydrological and physical responses of shallow slopes subject to rainfall events is vital for the efficiency of a warning system setup. In this research, a series of experiments were undertaken to evaluate the hydrological responses of shallow slopes of varying steepness and when subjected to varying intensities, periods, and inter-storm periods of rainfall. An analysis of infinite slopes was also undertaken to develop a fundamental understanding of rainfall-induced shallow slope failure characteristics. The hydrological and physical responses were characterized in the infiltration and saturation phases. During the infiltration phase, the maximum magnitude of water content was found behind the wetting front, termed as the water content behind the wetting front (θwb). For a certain soil type, the magnitude of θwb was found to be dependent on the magnitude of rainfall intensity, regardless of the slope gradient and initial water content. Based on the relative depth of the failure plane, the failure can be categorized by three prime modes: (i) along the impervious layer mode, (ii) shallow depth mode, and (iii) transitional mode. These modes can be characterized by the magnitude of a stability index termed as [Formula: see text] ratio. An infiltration index, termed as i/ks ratio, was found to play a role in the depth of the failure plane only for the transitional mode.

Investigation of a shallow slope failure on expansive clay in Texas

Highway slopes constructed with highly plastic clay soils undergo shrink-swell cycles during the wet-dry season, which usually soften the soil and may cause failure a few years following construction. There are two major wet-dry cycles in Texas, where summer to early fall is categorized as the dry period, and late fall to spring is categorized as the wet period. During this study, the failure of a highway slope located in Fort Worth, Texas was investigated, and the effect of rainfall on the slope failure was evaluated. The failure of the slope was investigated using soil test borings, geophysical testing, laboratory testing, slope stability analysis, and unsaturated flow analysis. The site investigation included sample collections from different depths of borings, determination of the soil index properties, and various shear strength testing to determine soil strength parameters. The obtained test results were further utilized in slope stability and flow analyses using the finite element method (FEM) in PLAXIS. The study indicated that both a fully-softened condition and rainfall were responsible for the slope failure. The fully-softened condition provided a factor of safety of 1.46, whereas the perched water condition after rainfall provided a nearly failing factor of safety of 1.05.

A general model for predicting the earthquake-induced displacements of shallow and deep slope failures

The accurate assessment of the stability of slopes during earthquakes has become a critical issue in seismically active areas. To readily evaluate seismic slope hazards in a region, we developed an empirical model for estimating seismic slope displacements for both shallow and deep types of failures (i.e., rigid and flexible sliding mass, respectively). The prediction model is simply a function of peak ground acceleration (PGA) and mean period of ground motions (Tm). For predicting displacement of shallow failure, the PGA and Tm of incident motion can be directly used in the model. For predicting the displacement of deep failure, however, the dynamic response of flexible sliding block interacts with the incident motion. The changed PGA and Tm, defined as kmax and Tm,k for the seismic loading of flexible sliding mass, respectively, is estimated depending on the natural period of sliding mass (Ts). Therefore, the predicting displacement of flexible mass is achieved using kmax and Tm,k in lieu of PGA and Tm in the developed rigid model. This general model provides a consistent approach for predicting the sliding displacement of shallow (rigid) and deep (flexible) slope failures.

Livestock tracks transform resource distribution on terracette landscapes of the Loess Plateau

AbstractStriking networks of livestock tracks, or terracettes, molded to the contours are a common feature on hilly rangelands of the semiarid Loess Plateau, one of the regions with the most severe soil erosion in the world. The formation of livestock tracks results in modified micro‐topography and ecological processes and leads to strong patterns in spatial distribution of vegetation, water, and nutrients. We investigated the spatial pattern of the topo‐edaphic, hydrological, biogeochemical, and biological attributes of these terracette landscapes and explored their potential implications to ecosystem functions. The results showed strong spatial heterogeneity in topo‐edaphic and biological structure of these landscapes, organized with three segments of a basic landscape unit—track, shoulder, and interslope. The above‐ and below‐ground biomass and soil nutrients concentrated in the shoulder segment forming a “band of fertility”. The network of livestock tracks likely reduced surface runoff and erosion by intercepting runoff and facilitate infiltration, while posing little risk of increasing shallow slope failures given the structure of loess soil. There appears a positive feedback loop for maintaining the structure of terracette landscapes. Trampling by goats maintains the tracks, which leads to spatial heterogeneity in biophysical structure and processes. The network of tracks enabled the goats to travel and graze in ways that reduce energy expenditure and increase foraging efficiency, which leads to strongly preferential use of the tracks by the goats. There are also evidence of a possible process resemble a slope parallel retreat at a micro‐scale, which may result in upslope movement of the terracettes. There may be important functional differences between landscapes with and without networks of livestock tracks, in regulating water runoff and soil erosion, forage production, and soil carbon storage. These functional differences may have significant implications to land use policies and practices aiming at soil and water conservation and socioecological sustainability of the Loess Plateau.

Influence of swelling behavior on the stability of an infinite unsaturated expansive soil slope

The influence of the stress regime change and associated softening can be significant on unsaturated expansive soil slope stability due to soil swelling upon wetting, which cannot be considered in conventional hydrological models. In this paper, the shallow expansive soil slope failure mechanism is addressed in the framework of an infinite slope formulation. The unsaturated soil elasto-plastic constitutive relationship is utilized for interpretation of stress regime evolution induced by expansive soil swelling during infiltration. The extended Mohr–Coulomb failure criterion for unsaturated soils is used as the yield surface, under which the nonlinear elastic behavior is considered by quantifying the effect of two stress state variables (net stress and suction) on elasticity parameters. The strain softening behavior in unsaturated soils is accounted for via reducing the material parameters of the yield surface with respect to plastic deviatoric strain. A numerical exercise is performed on a relatively gentle slope in Regina, Canada with highly expansive soil properties, using the developed computer program that implements the constitutive model into infinite slope formulation. The results suggest that neglecting the swelling-induced stress change and associated softening behavior can significantly overestimate the stability of expansive soil shallow layer under infiltration, in terms of both failure occurrence and failure time. Additional parametric study shows that all the considered parameters (including initial stress condition, softening rate and slope angle) have a considerable effect on the failure time and failure depth of the shallow deposit, which have important implications for the engineering design of expansive soil slopes.

Regional modeling of rainfall-induced landslides using TRIGRS model by incorporating plant cover effects: case study in Hulu Kelang, Malaysia

The objective of this paper is to develop a spatial temporal regional modeling of local rainfall patterns effect on the plant cover slopes in Hulu Kelang area. Rainfall interception, tree root cohesion, and tree surcharge were considered as main plant cover effects on the slope stability. In this regard, an improved version of the Transient Rainfall Infiltration and Grid-based Regional Slope stability model (TRIGRS) was performed using Microsoft Excel® and GIS framework system for coupled hydrological–mechanical modeling of rainfall-induced landslide by incorporating plant cover effects. The infiltration process of the improved model was integrated with the precipitation distribution method and rainfall interception approach while the slope stability analysis of TRIGRS model was replaced with the improved analysis with consideration of root cohesion and tree surcharge. In the following, the spatial temporal analysis of slope failures was performed using the monthly average rainfall during two different monsoon seasons of 2008 and 2009 for triggering shallow slope failure in Hulu Kelang area. The corresponding changes in pressure head and consequent water table depth were calculated during two monsoon seasons. Subsequently, factor of safety is computed using local rainfall patterns, along with root coefficient and tree surcharge in the study area. The results showed the plant-covered slopes are inducing an overestimation of the slope failure susceptibility using existing TRIGRS model, while the improved model resulted that less landslide susceptible areas were more representative of the actual stability conditions of the slopes at the study area.

Undrained shear strength characteristics of compacted clay reinforced with natural hemp fibers

Reinforcing clay with natural fibers is a common practice in various applications, such as the construction of steep slopes, repair of shallow slope failures, improving the performance of landfill covers, strengthening of roadbeds, etc. The reliance on this technique is on the rise as a result of the increasing demand for incorporating sustainable materials in construction. “Hemp” fibers are natural fibers derived from the plant Cannabis Sativa. Industrial Hemp is legally cultivated in a number of countries. Hemp is used in several industries, such as paper, textiles, clothing, biodegradable plastics, construction, body care products, food, medicine, and biofuel, in addition to applications in strengthening concrete and soils. The main objective of this paper is to investigate the potential use of natural Hemp fiber in improving the load response of compacted clays. A laboratory-testing program consisting of 18 unconsolidated undrained triaxial tests was designed for this purpose. Specimens of control clay and of clay mixed with Hemp fibers added at various fiber contents were prepared at a number of water contents and compacted using the standard proctor procedure. Specimens with diameters of 7.15 cm and heights of 14.3 cm were prepared at varying moisture contents (14%, 18%, and 20%) and mixed with fibers of 4 cm length at gravimetric contents ranging from 0.5% to 1.5%. Results show that improvements in shear strength of up to 100% could be realized for the Hemp reinforced specimens. The percent improvement increases with the fiber content up to a threshold value of 1.25% and differs depending on the magnitude of the water content used in compaction in reference to the optimum moisture content of the matrix clay.

Likely Scenarios of Natural Terrain Shallow Slope Failures on Hong Kong Island under Extreme Storms

AbstractIn Hong Kong, rain-induced shallow slope failures are recognized as one of the most catastrophic hazards due to Hong Kong’s hilly terrain and frequent heavy storms. Due to climate changes, extreme storms are expected to be more frequent and intense in the future. The prediction of shallow slope failures under extreme storms is therefore essential. This study aims at simulating likely shallow slope failures on western Hong Kong Island under extreme storms. The terrain and slopes are discretized into a grid of cells on a geographical information system. Then, the pore-water pressure regime in the ground is analyzed through an infiltration analysis. Next, the slope stability and debris movement are assessed using a well-established model, which has been validated with landslides triggered in two past storm events. Finally, the shallow slope failures under three extreme storms at 44, 65, and 85% of the probable maximum precipitation are simulated. Under such extreme storms, more than 300 major slope f...

Improved measurement of soil moisture using an ultrasonic waveguide to predict rainfall-induced slope failure

Field monitoring of soil moisture and groundwater level is important to predict shallow slope failure stemming from heavy rainfall. We previously proposed a monitoring technique using ultrasonic waveguides in which soil moisture and groundwater levels are monitored on the basis of the intensity and propagation time of ultrasonic waves reflected from the underground soil surface, respectively. In field monitoring, the reflective intensity depends on the depth of monitoring points and the inhomogeneity of grains, so it has been difficult to examine the reflective intensity change quantitatively. In the present work, we propose improvements that will allow us to measure the intensity change quantitatively. Specifically, we utilize an ultrasonic waveguide of a constant length by using casing pipes with different lengths depending on the monitoring depth and cover the surface of coarse-grained soil with a homogeneous fine soil to obtain repeatable data for wetting and drying cycles. The positive effects of these improvements were confirmed by a field monitoring test.

Slope Stabilization Using Recycled Plastic Pins

AbstractShallow slope failures are common in highway embankments in the north Texas region and pose significant maintenance problems for the Texas Department of Transportation (TxDOT). As a cost-effective alternative, recycled plastic pins (RPPs) can be utilized to stabilize slopes and prevent shallow slope failures. RPPs are fabricated from recycled plastic and waste materials (i.e., polymers, sawdust, and fly ash). It is a lightweight material and less susceptible to chemical and biological degradation than alternative reinforcing elements. RPPs are driven into the slope face, which provides additional resistance along the slip surface, increasing the factor of safety against shallow slope failure. The current study presents a field demonstration project of a highway slope reinforced with RPPs. The slope was located on the southbound side of U.S. Highway 287, near the St. Paul overpass in Midlothian, Texas. Surficial movement had taken place in the slope, resulting in cracks along the shoulder near the ...

Factors influencing the formation of shallow landslides in the Boston Mountains of northwest Arkansas, USA

Slope failures cause billions of dollars of damage annually and put human lives at risk. This study employed field measurements and observations to provide the framework for laboratory simulations to investigate the effects of environmental characteristics on slope stability in the highly fractured bedrock region of the Boston Mountains, northwest Arkansas. Field measurements, to determine characteristics and possible controls of 10 shallow slope failures along an interstate highway, revealed that slope failures occurred within a relatively narrow range of slope angles (17–36°) and in loamy soils. Based on field observations, flume experiments were conducted to investigate the relationships between soil texture, slope angle, bedrock fractures, soil compaction, and slope instability. Time to failure differed (p < 0.05) among treatment combinations. Generally, slopes composed of loam were more stable than slopes composed of sand. Time to failure decreased more on slopes of 15–20° than on slopes of 20–25°. Flume slopes with sod cover never failed. This study provided a methodology for using field analyses of slope failures to guide laboratory experiments and demonstrated that complex interactions among environmental factors work to stabilize or compromise steep (>20°) slopes.

Very shallow dyke intrusion and potential slope failure imaged by ground deformation: The 28 December 2014 eruption on Mount Etna

AbstractOn 28 December 2014, eruptive activity resumed at Mount Etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano. Unlike all previous summit activity, this eruption produced clear deformation at the summit of the volcano. GPS displacements and Sentinel‐1A ascending interferograms were calculated in order to image the ground deformation pattern accompanying the eruption. The displacements observed by GPS depict a local ground deformation pattern, affecting only the upper part of the volcano. Despite snow cover on the summit, differential interferometry synthetic aperture radar (DInSAR) data allowed obtaining more detail on the ground deformation pattern on the upper eastern side of the volcano. Three‐dimensional GPS displacements inversion located a very shallow NE‐SW intrusion just beneath the New Southeast Crater. However, this model cannot justify all the deformation observed by DInSAR thus revealing a gravitational failure of the lava flow field.

기반암 경계조건을 적용한 Green-Ampt 침투모델에 의한 사면의 얕은 파괴 해석

세계의 많은 지역이 강우에 의한 사면파괴에 취약하다. 우리나라는 풍화잔류토 층의 깊이가 얕고 호우가 빈발하여 포화대가 지표로부터 하강하면서 기반암에 도달하여 토층 전체가 포화상태에 이르는 침투거동이 사면파괴를 일으키는 중요한 원인 중 하나이다. 따라서 파괴면의 깊이가 얕고 풍화토층과 기반암의 경계면 근처에 형성되는 특징을 가지고 있다. 본 연구에서는 한계평형법에 바탕을 둔 사면의 얕은 파괴 해석을 위하여 경사면을 고려한 일차원 침투모델인 Green-Ampt 모델을 적용하였다. 시간에 따라 변하는 강우강도를 고려하였으며 얕은 토층을 고려하기 위하여 Green-Ampt 모델에 얕은 기반암의 경계조건을 도입하였다. 해석결과에 의하면 제안된 해석법은 사면에 대한 강우의 침투 평가 시 포화대의 기반암으로의 진행을 계산함으로써 강우의 침투거동을 사면안정에 적절하게 반영할 수 있음을 보여준다. Many regions around the world are vulnerable to rainfall-induced slope failures. In Korea, the depth of weathered residual soil is shallow and rainfall of strong intensities is frequent. Therefore, saturation of whole soil layer caused by the reaching of saturated wetting front from the slope surface to impermeable bedrock by rain infiltration is one of important causes of slope failure. This leads to the shallow depth of slope failure that passes through the interface between soil and impermeable bedrock. In this study, one-dimensional Green-Ampt model on sloping surfaces in infiltration analysis is used for the shallow slope failure analysis based on the limit equilibrium method. Time-varying intensity of rainfall was considered and shallow impermeable boundary condition was imposed in the Green-Ampt model to simulate the impermeable bedrock underlying the shallow residual soil. The results of example analysis showed that the proposed method can be used to efficiently consider the rainfall infiltration behavior caused by shallow impermeable bedrock boundary in stability assessment of infinite slope.

Spatiotemporal regional modeling of rainfall-induced slope failure in Hulu Kelang, Malaysia

This study demonstrated the use of transient rainfall infiltration and grid-based regional slope stability analysis model incorporated with spatial rainfall distribution model for regional mapping of rainfall-induced slope failures in a slope failure-prone area in Malaysia, namely Hulu Kelang. Infinite slope analysis was incorporated into the improved model to compute the pore water pressure and slope stability of the region. Digital terrain maps, spatial rainfall distributions, soil profiles, groundwater table, and soil properties were input into the model. The results showed that the slope failures in the study area can be grouped into shallow failures (<4 m) and sub-shallow failures (4–8 m). Most of the shallow slope failures (<4 m) were triggered by the northeast monsoon while the NE monsoon that characterized by more prolonged and intense rainfalls. Spatial temporal distributions of shallow and sub shallow slope failures predicted using the improved model showed reasonably good comparison with the historical slope failure regions. Monsoon events have affected slope stability by reduction in matric suction, complete loss of matric suction, and development of positive pore water pressure (PWP). Computation for the effects of rainfall infiltration on PWP response and consequent effects on slope stability is enhanced by the spatial rainfall distribution model. The pore water pressure response to monsoon rainfall is a function of rainfall duration, the rate of infiltration, groundwater depth, soil thickness, and slope inclination. The amount of the local daily rainfall is not the only factor affecting slope stability. The prolonged antecedent rainfall could have a role to play in building up the slope failure mechanism.