Clay Slopes Research Articles

Model updating for slope stability assessment in spatially varying soil parameters using multi-type observations

With site-specific information, model updating can calibrate the probability distributions of material parameters, and the updated distributions can be further utilized to facilitate a more realistic slope reliability assessment. Many model updating methods have been proposed, while the inherent spatial variability of material properties is scarcely discussed in the literature, mainly due to the curse of dimensionality when considering thousands of random variables. The BUS (Bayesian updating with structural reliability methods) algorithm can well tackle the high-dimensional problem by converting it into an equivalent structural reliability problem. The BUS algorithm can integrate monitoring data and field observations to back analyse stability parameters. However, when generating a conditional random field using a large number of in-situ test data, the BUS algorithm becomes less efficient because low acceptance probability often occurs, while the Kriging algorithm is applicable for this situation. This study proposes an effective approach for model updating that combines Kriging-based conditional random field with the BUS algorithm to integrate multi-type observations. To illustrate the effectiveness of the proposed approach, an undrained saturated clay slope with a spatially varying soil parameter is taken as an example. The results indicate that the proposed approach is able to update the probability distribution of spatially varying soil parameters and update the slope reliability using multi-type observations with reasonable calculation efficiency.

Seismic Centrifuge Modeling of a Gentle Slope of Layered Clay, Including a Weak Layer

Abstract This article presents a model preparation methodology for simulating the seismic behavior of a gentle slope in clay with the presence of a soft, weak layer employing centrifuge testing. The model consisted of a three-layered slope of relatively soft clay with a 3° inclination, representative of Brazilian marine subsoils. In-flight characterization of the undrained shear strength and shear wave velocity profiles were achieved through T-bar penetrometer and air hammer tests. The model was subjected to a series of earthquake simulations at different amplitudes, and the response was tracked with accelerometers and displacement transducers. Additional data were obtained using a particle image velocimetry (PIV) methodology also described in this work. The results show that the proposed model preparation methodology enables the simulation of the strength contrast between the weak and relatively stronger surrounding layers using a laminar container. The additional displacement and acceleration data obtained from the PIV were in good agreement with the corresponding displacement transducer and accelerometer measurements. From the spectral analysis, a shift in the fundamental period was observed as the strain amplitude was increased, suggesting that strain rate effects mobilize higher stresses and a strength rate correction should be considered for the calibration of numerical models and comparison with existing methods for calculation of dynamic displacements in slopes.

Assessing the influence of the hydraulic boundary conditions on clay slope stability: The Fontana Monte case study

Recent studies have assessed that slope-vegetation-atmosphere, SLVA, interaction may trigger the activity of deep landslides in clayey slopes. In some cases, the presence of an underground aquifer, fed by an upstream hydraulic recharging area, may represent a predisposing factor of such activity, being co-responsible of deep piezometric heads, which can undergo seasonal fluctuations due to the SLVA interaction. In this perspective, the present paper illustrates the results of a scientific research, carried out in a pilot site of the Daunia Apennines, the Fontana Monte slope at Volturino (Foggia, Italy), considered as a prototype of the class of landslide mechanisms controlled by both the rainfall water infiltration and the presence of a water-bearing aquifer in the hillslope.Numerical simulations of the saturated/partially saturated transient seepage flow in the slope have been performed by means of uncoupled hydraulic finite element analyses, with the aim of investigating the sources of large piezometric heads, related to climatic, hydrogeological and hydraulic slope features. The rainfall and evapotranspiration fluxes, the latter defined through the FAO Penman-Monteith method, are both implemented as ground surface input, while seasonal variations of the upstream hydraulic boundary conditions are imposed to predict the seasonal piezometric excursion at shallow and deep monitoring points. The transient seepage results are then used as input for limit equilibrium analyses to assess the influence of the hydraulic settings on the stability of the considered landslide body. The work shows the impact of both climatic and hydraulic factors on the seepage processes, affecting the stability of the slope. Moreover, it is highlighted that the accurate implementation of the upstream hydraulic feeding is fundamental for a reliable prediction of the monitored piezometric regime, strictly related to the recharge of the water-bearing aquifer.

Temperature and soils predict the distribution of plant species along the Himalayan elevational gradient

AbstractTropical montane systems are characterized by a high plant species diversity and complex environmental gradients. Climate warming may force species to track suitable climatic conditions and shift their distribution upward, which may be particularly problematic for species with narrow elevational ranges. To better understand the fate of montane plant species in the face of climate change, we evaluated a) which environmental factors best predict the distribution of 277 plant species along the Himalayan elevational gradient in Nepal, and b) whether species elevational ranges increase with increasing elevation. To this end, we developed ecological niche models using MaxEnt by combining species survey and presence data with 19 environmental predictors. Key environmental factors that best predicted the distribution of Himalayan plant species were mean annual temperature (for 54.5% of the species) followed by soil clay content (10.2%) and slope (9.4%). Although temperature is the best predictor, it is associated with many other covariates that may explain species distribution, such as irradiance and potential evapotranspiration. Species at both ends of the Himalayan elevational gradient had narrower elevational ranges than species in the middle. Our results suggest that with further global warming, most Himalayan plant species have to migrate upward, which is especially critical for upland species with narrow distribution ranges.

Upper Bound Analysis of the Stability of 3D Slopes in the Saturated Soft Clay Subjected to Seismic Effect

In order to study the three-dimensional stability problem of the saturated soft clay slope under earthquake loads, based on the three-dimensional rotation failure model, the seismic force was introduced into the calculation by the quasi-static method. The work rate of external loads and the internal energy dissipation rate of the saturated soft clay slope were calculated using the upper bound method of limit analysis, and the analytical solution of stability coefficient of saturated soft clay slopes was derived based on the fictitious power principle. By virtue of the exhaust algorithm, the optimal solution of stability coefficient of saturated soft clay slopes was obtained. The influence of the slope angle and the horizontal and vertical seismic forces on the stability coefficient of saturated soft clay slope was analyzed. The results show that the slope angle has a great influence on the stability coefficient, and the relative difference is up to 35.7%. Therefore, the stability coefficient of saturated soft clay slopes can be effectively increased by a proper slope setting. The horizontal and vertical seismic forces also have a significant influence on the stability of saturated soft clay slopes. The relative differences of the stability coefficient under horizontal and vertical seismic forces are as high as 41 and 14.7%, respectively. If they are ignored, the stability coefficient of saturated soft clay slopes will be seriously overestimated. It is suggested that the effects of horizontal and vertical seismic forces must be considered simultaneously in the seismic design of saturated soft clay slopes.

New discovery of Opuntia humifusa (Cactaceae) in the vicinity of Kyiv

Наводяться дані щодо нової знахідки інвазійного виду Opuntia humifusa (Raf.) Raf. (Cactaceae A.L. Juss.) з материкової частини території України (околиці села Ходосівка Обухівського району Київської області). Описано нововиявлене місцезнаходження, охарактеризовано малочисельну популяцію виду. Наводиться кількість виявлених локацій у межах популяції – 5, а також кількість знайдених екземплярів – 11. Охарактеризовано вікові спектри особин популяції O. humifusa. Переважаючими віковими станами є генеративні – 45,5 %, що вказує на успішну акліматизацію та натуралізацію виду в умовах лісостепової зони України. Зроблено геоботанічні описи та вказано синтаксономічні особливості місцезростань O. humifusa. Особини цього виду властиві стрімким рухливим глинистим схилам в урочищі «Планерна гора», де вони віднесені до угруповань класів Festuco-Brometea Br.-Bl. et Tx. in Br.-Bl. 1949 та Artemisietea vulgaris Lohmeyer, Preising et R.Tüxen ex von Rochow 1951. Рослинність рудералізованих степових місцезростань O. humifusa є флористично збідненою з розрідженим травостоєм. Популяції притаманні рухливим схилам (кут нахилу до 35–40°), на яких відбуваються ерозійні процеси. Загальне проективне покриття угруповань коливається у діапазоні 50–90 %, зменшуючись на стрімких схилах і зростаючи на пологих. Висловлюється припущення про ймовірне джерело заносу діаспор O. humifusa в околиці міста Києва та шляхи її експансії з півдня на північ. Зазначається пріоритетність насіннєвого розмноження O. humifusa, зумовленого антропохорним переносом. Показано шляхи акліматизації цього виду у різні регіони материкової України, натуралізацію у природні степові фітоценози степової зони та поширення у природні рослинні угруповання лісостепової зони. З огляду на сучасні кліматичні зміни та тенденцію розповсюдження O. humifusa, цей інвазійний вид потребує подальшого моніторингу поширення на території України з розробкою відповідних попереджувальних заходів.

Limit analysis solutions for stability factor of unsupported conical slopes in clays with heterogeneity and anisotropy

The novel stability solutions of unsupported conical slope in anisotropic and inhomogeneous clays utilizing the lower-bound (LB) and upper-bound (UB) finite-element limit analyses (FELA) are proposed in this paper. The anisotropic undrained shear (AUS) model and linear increasing undrained shear strength are employed to determine the anisotropic and inhomogeneous soil behavior, respectively. The stability factor [Formula: see text] is obtained with the variations of dimensionless parameters including the ratio of anisotropic ([Formula: see text], the rate of increasing undrained shear strength ([Formula: see text], the ratio between the height and the radius at the bottom slope ([Formula: see text]/[Formula: see text], and the inclination angle of slope ([Formula: see text] provided in sample charts. The failure patterns of conical slope considering the affected parameters are also obtained and described.

Stability analysis of an unsaturated clay slope based on the coupled effect of temperature and saturation

In view of clay slope instability caused by environmental temperature and rainfall infiltration in summer and autumn, the mechanism of the effect of temperature and saturation on unsaturated clay slope stability is discussed. To achieve this objective, this study uses theoretical and numerical methods. Based on the theory of unsaturated clay and the law of heat conduction, the relationship between cohesion and matrix suction of unsaturated clay was derived considering the influence of temperature and saturation. Taking into consideration the effects of temperature and saturation, the coupling equation for the shear strength of unsaturated clay was constructed under conditions of rainfall infiltration. The coupling equation for temperature and saturation was used using the strength reduction method, and the slope stability was analysed using FLAC software. The results show that: (i) cohesion in the unsaturated clay slope increases with increasing depth; (ii) the safety factor is smaller when taking into consideration the coupled effect of temperature and saturation than when the temperature effect is not taken into consideration; and (iii) the clay slope is unstable when the coupled effect of temperature and saturation is taken into consideration, but is stable when the coupled effect of temperature and saturation is not considered and soil saturation reaches 80%. Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes

Strength parameter selection framework for evaluating the design life of clay cut slopes

The design of engineered earthworks is predominantly conducted through limit equilibrium analysis, requiring strain-independent strength criteria. Previous studies on deep-seated first-time failures within over-consolidated clay cut slopes have proposed the use of fully softened strength parameters for design. A study investigating shallow first-time failures in clay cut slopes due to seasonal stress cycles was undertaken using a validated numerical model capable of capturing seasonal ratcheting and progressive failure. It was found that fully softened strength criteria are inappropriate for the assessment of shallow first-time failures due to seasonal ratcheting and slopes at angles between the material's fully softened and residual friction angle may be at risk of failure in the future due to this behaviour. However, adopting residual strength parameters will likely result in overly conservative solutions considering the required design life of geotechnical assets. It was found that the strain-softening behaviour of clay defines the rate of strength deterioration and the operational life of engineered slopes. While general guidelines for analysis considering shallow first-time failures in clay cut slopes are provided, detailed understanding of a material's strain-softening behaviour, the magnitude and rate of strength reduction with strains, is needed to establish strength criteria for limit equilibrium analysis.

Retraction Note to: Slope ecological restoration based on image classification and construction of sports fitness index

This study uses literature method, comparative research method, qualitative and quantitative multiple demonstration method, Delphi method, analytic hierarchy process and survey method, image classification, mathematical statistics based on local characteristics and international experience, and other research methods to explore the construction of national and international children and youth sports fitness evaluation index system. In the process of construction, it is the first to establish the development history of Chinese children and adolescents’ physical quality assessment. Secondly, following the specific program design, we use and optimize the child and adolescent grade index system and verify the child and adolescent physical condition grade model. Finally, the paper puts forward the suggestion of sustainable utilization evaluation index system to promote the health of children and young people. This paper also studies the exposed slopes produced by a large number of slope engineering in the process of highway construction. It has the problems of weak soil structure and insufficient plant coverage. The slope problem of highway laterite in rainy area A is particularly serious. It is very important to adopt necessary slope ecological restoration for slope safety and stability, soil and water conservation, and plant community reconstruction. According to the disease characteristics of red clay slope in a rainy area, this paper analyzes the ecological principle and plant quarantine mechanism of slope ecological restoration, takes into account the two main characteristics of poor erosion resistance of slope, and introduces three new functional materials: red clay and low slope, nutrient content of slope, and artificial soil and soil stabilizer for erosion control. It promotes the further research on ecological restoration technology of red clay slope.

Examining the Effects of Suction and Nonlinear Strength Envelopes on the Stability of a High Plasticity Clay Slope

Slope failures in high plasticity clay deposits are common occurrences in many parts of the world. In western and central Alabama, expansive Prairie clays are commonly found, and shallow slope failures have occurred in both fill and cut slopes containing these high plasticity clays. The objective of this study was to examine the effects of suction and the use of nonlinear strength envelopes on the embankment stability of a section of highway AL-5. The testing program consisted of fifteen ring shear tests performed using a Bromhead Ring Shear Device. The results of the tests were used to develop both linear and nonlinear fully softened and residual strength envelopes. The saturated strength envelopes are then used in a limit equilibrium slope stability analysis with and without the effects of suction. The results show stability (factor of safety >1) for all cases except the residual friction angle without suction. Given these results, large slope failures are unlikely to occur in this area, but surficial failures and deformations due to creep may be possible. These results demonstrate the importance of considering the effects of suction and nonlinear strength envelopes when examining the potential for shallow slope failures in high plasticity clays.

Catastrophic failure of submarine slopes with elastic shearing zones

Submarine landslides can be devastating to offshore facilities and coastal areas. This study explores the triggering mechanisms of catastrophic failure of an infinite planar slope in sensitive soil deposits under undrained conditions. The strain-softening behaviour of sensitive soils can cause rapid growth of the shear band along a thin layer of weak materials and ultimately lead to a large landslide. A new analytical criterion for catastrophic shear band propagation taking into account elastic shear deformation in the shear band was derived using a process zone approach. A mechanical analysis was conducted on the fully softened zone, end zone and elastic shearing zone, among which the evolution of the shear band and the development of key mechanical variables were presented to illustrate the formation mechanism of the large submarine planar landslides. The influences of the elastic properties of soils on the initiation of catastrophic failure were investigated for both clay and sand slopes, demonstrating that the consideration of the elastic properties result in a more conservative failure criterion compared with that presented in the previous study.

A novel implicit coupled hydro-mechanical SPFEM approach for modelling of delayed failure of cut slope in soft sensitive clay

Modelling of delayed failure of cut slopes in soft sensitive clays is a significant challenge because of three major features taking place simultaneously: large deformation of the slope up to failure, pore water pressure generation and dissipation in the slope, and complicated time-dependent deformation of sensitive clay. This paper proposes a novel fully hydro-mechanical coupled edge-based strain smoothed particle finite element (ES-PFEM) modelling approach for delayed failure of cut slope with three outstanding features: (1) the particle finite element method with low-order edge-based strain-smoothed element for large deformation analysis, (2) an efficient stabilization method for pore water pressure to circumvent the Babuška-Brezzi stability restriction and (3) the elasto-viscoplastic model considering time-dependency, anisotropy and destructuration of soft sensitive clays. The accuracy and efficiency of the proposed approach are first examined by simulating consolidation test and strip footing. Furthermore, an adaptive substepping algorithm is proposed for the elasto-viscoplastic model. Finally, a typical case of delayed failures of cut slopes with different angles in soft sensitive clays is simulated and analysed, demonstrating the predictive ability of the proposed approach. The relationship between slope angle, sensitivity of clay and time of failure occurring is obtained for predicting the slope failure time in practice.

Effects of desiccation cracks and vegetation on the shallow stability of a red clay cut slope under rainfall infiltration

Red clay, an easily cracking lateritic soil, is extensively distributed in southern China. Cracked red clay slopes often show shallow failures under rainfall, which is challenging to reproduce by finite element methods. This study aims to examine how desiccation cracks and vegetation affect the shallow stability of a red clay cut slope during rainfall. Numerical models of the slope are created using ABAQUS, and an effective approach is proposed to simulate the distribution of desiccation cracks. The reliability of the numerical models and approaches is validated against field surveys. Parametric analysis is then conducted to investigate the influences of rainfall parameters, crack parameters and vegetation parameters on the slope stability. The results demonstrate that the presence of desiccation cracks can cause shallow failure and greatly reduce the factor of safety of the slope. This indicates that control of crack development is important to maintain slope safety. Moreover, the stability of cracked slopes can be obviously improved by vegetation with roots longer than 0.5 m. A tap root system appears to perform better than a fibrous root system. However, shallow-rooted vegetation may also contribute to the shallow stability of the slope by restraining the formation of desiccation cracks.

Stability Analysis of Unsaturated Red Clay Slope under Different Heavy Precipitation Patterns

A fluid-solid coupling numerical model was established for unsaturated red clay, which is prone to causing clustered landslides under three typical heavy precipitations in southwest China, to investigate the influence of the precipitation patterns on the infiltration mode, pore water pressure and stability of unsaturated red clay slopes. The investigation showed that (1) during heavy precipitation, much rainwater tends to form a transient saturated zone in the shallow layers of the slopes in a short time, thereby reducing the matric suction of the soil matrix; (2) under short-term continuous rainstorm, the pore water pressure dropped to the greatest extent; and (3) the safety factor experienced the largest decrease under persistent heavy precipitation following 24-hour rainfall, while slopes displaced the most under sudden rainstorm.

Sensitivity Analysis of Anchored Slopes under Water Level Fluctuations: A Case Study of Cangjiang Bridge—Yingpan Slope in China

This paper presents an improved slope stability sensitivity analysis (ISSSA) model that takes anchoring factors into consideration in umbrella-anchored sand and clay slopes under reservoir water level fluctuation. The results of the ISSSA model show that the slope inclination and the layout density of anchors are the main controlling factors for sand slope stability under fluctuation of the water level, while the slope inclination and water head height are the main controlling factors for slope stability in the Cangjiang bridge—Yingpan slope of Yunnan province in China. Moreover, there is an optimum anchorage angle, in the range of 25–45 degrees, which has the greatest influence on slope stability. The fluctuation of the reservoir water level is an important factor that triggers slope instability; in particular, a sudden drop in the surface water level can easily lead to landslides; therefore, corresponding measures should be implemented in a timely manner in order to mitigate landslide disasters.

Analysis of Laterally Loaded Piles in Undrained Clay Concave Slope

A concave slope is a common type of slope. This paper proposes a simplified method to study the effect of a clay concave slope on laterally loaded piles. The hyperbolic p - y curve model is selected as the lateral pile-soil interaction model of the concave slope. Considering the two angles of the concave slope, the variation of the ultimate soil resistance with depth is divided into two parts, and the ultimate soil resistance varies nonlinearly with depth. The reduction factor method and normalization method are used to obtain the initial stiffness. The theoretical results will be compared with the calculation results of the 3D FE analysis to prove the rationality of this method. Finally, the simplified method is used to analyze the response of laterally loaded piles under different parameters.

Modelling earthquake-triggered landslide runout with the material point method

Landslides triggered by earthquakes cause devastating consequences to downstream infrastructure. The simulation and prediction of these large-strain events remain challenging. The objectives of this work were to validate the material point method (MPM) framework for the study of coseismic landslides and to compare the capabilities of the MPM with mesh-based methods and simplified Newmark-type methods to simulate post-failure runouts. To achieve these objectives, the MPM framework was used whereby a nodal kinematic boundary condition was employed with a moving mesh. The framework was validated with a shaking table laboratory test of a saturated clay slope. A parametric analysis was then conducted using 25 real ground motions on a simple theoretical slope. The MPM results were compared with those obtained with mesh-based methods and three state-of-the-art Newmark-type approaches. The mesh-based methods were consistent with MPM predictions for small-strain instabilities associated with low-energy ground motions (i.e. Arias intensity lower than 4 m/s). When using ground motions with energy above this threshold, mesh-based methods accumulate significant errors associated with bad geometry. The MPM results consistently matched permanent displacements predicted with the Newmark-type methods employed in this analysis.

Erratum to “Regional Stability Analysis of Red Clay Slope Based on Different Failure Modes: A Case Study in Taizaifu Area, Fukuoka”

Erratum to “Regional Stability Analysis of Red Clay Slope Based on Different Failure Modes: A Case Study in Taizaifu Area, Fukuoka”

Effect of Vegetation Roots on the Threshold of Slope Instability Induced by Rainfall and Runoff

Although vegetation is increasingly used to mitigate landslide risks, how vegetation roots affect the landslide threshold of slope has rarely been explored, particularly in the case of lateral runoff. In this study, we established a two-dimensional saturated-unsaturated infiltration equation considering the hydraulic effects of vegetation roots. The analytical solution for the shallow unsaturated two-dimensional coupled infiltration of vegetated slope (VS) was obtained by a Fourier transform technique. The numerical method was used to evaluate the stability of VS caused by four root architectures, the rainfall amount, and the rainfall duration. Subsequently, the transformation law in runoff, vegetation evaporation, and landslide threshold was analyzed. The results indicate that the factor of safety (FOS) increases with increasing drying time and decreases with increasing depth; the minimum FOS is at the junction of the root-rootless zone. Runoff and vegetation evaporation are favorable for the shallow stability of VS. The time of the safe area is 35 h for rainfall amount 500 m in the uniformly root clay slope. Moreover, four landslide threshold curves that reflected the root architecture, rainfall amount, and rainfall duration are developed, which are more realistic than those created using one-dimensional instability modeling.