Unsaturated Soil Slope Research Articles

Hydromechanical behaviour of a slope reinforced by grass roots under rainfall conditions

Soil bioengineering using vegetation has been considered an environmentally friendly solution to improve slope stability. Although several studies have demonstrated the contribution of vegetation to slope stability, a gap in understanding the mechanisms of grass root–soil interactions under rainfall conditions remains. This study investigates the effects of the roots of vetiver grass (Chrysopogon zizanioides) on the hydromechanical behaviour of an unsaturated soil slope using the centrifuge modelling technique. The changes in pore water pressure and slope deformation were monitored during the test. The monitored data were subsequently back-analysed and interpreted using seepage–stability analyses. In addition, this study focused on evaluating the effect of roots on slope stability, considering safety and pore water pressure during rainfall. Results revealed that the vetiver roots remarkably affected the initial suction of the slope by increasing the soil's air-entry value. The increased suction and the additional cohesion provided by the roots enhanced slope stability under rainfall conditions.

Three-Dimensional Stability of Unsaturated Soil Slopes Strengthened through Frame Beam Anchor Plates under Steady Seepage Conditions

Three-Dimensional Stability of Unsaturated Soil Slopes Strengthened through Frame Beam Anchor Plates under Steady Seepage Conditions

Research on The Interaction Mechanism and Stability Analysis of Unsaturated Soil Slope and Support Structure

Research on The Interaction Mechanism and Stability Analysis of Unsaturated Soil Slope and Support Structure

Rainfall Infiltration Test and Numerical Simulation Analysis of a Large Unsaturated Soil Slope

Rainfall Infiltration Test and Numerical Simulation Analysis of a Large Unsaturated Soil Slope

The three-dimensional stability analysis of piled slopes in unsaturated and inhomogeneous soils with nonlinear failure criterion

Under the nonlinear Mohr-Coulomb (MC) failure criterion, based on the upper-bound limit analysis theorem, the three-dimensional(3D) stability of piled unsaturated inhomogeneous slopes is analyzed. By incorporating the nonlinear strength parameters c t and φ t, the energy balance equation is established, and the explicit expression of slope safety factor (F S) is derived by the gravity increase method (GIM). In addition, a genetic algorithm (GA) is used to calculate the minimum F S. The results obtained were compared with those of existing literature to verify the effectiveness of the method used in this paper. The influence of nonlinear parameters on slope stability was studied through parameter analysis. The results show that the nonlinear parameters of soil have a significant influence on the stability of piled slopes. The F S increases with the increase of nonlinear coefficient and uniaxial tensile strength and decreases with the increase of initial cohesion of soil. In addition, the critical slip surface of the slope becomes shallower with the weakening of soil nonlinearity. Furthermore, ignoring the suction effect will overestimate the slope stability, and the slope stability intensified with decreased soil inhomogeneity.

Investigation of rainfall-induced landslide on unsaturated lateritic residual soil slope in Nilgiris, Western Ghats, India using deterministic and reliability analysis

Investigation of rainfall-induced landslide on unsaturated lateritic residual soil slope in Nilgiris, Western Ghats, India using deterministic and reliability analysis

Numerical study on the rupture behavior of funicular liquid bridge between three spheres

Owing to the increase in saturation, unsaturated soil slopes are prone to experiencing landslides and mudflows during the rainy seasons. As liquid volume rises, the funicular regime between multiple particles gradually replaces the pendular regime within unsaturated granular soil. This study establishes a numerical model of a funicular liquid bridge between three spherical particles using the Surface Evolver software. The equilibrium state of the funicular bridge was examined using energy-minimization methods. The effects of liquid volume, contact angle, upper particle-pair gap, and separation distance on the capillary force and rupture distance were investigated. Finally, the relationship between capillary force and rupture distance is further elucidated based on meniscus profiles.

Slope stability analysis based on rate-dependent soil-water characteristic curve

Rainfall-induced landslides are a common geological hazard. Analyzing this problem necessitates the use of the unsaturated soil theory, with the soil-water characteristic curve (SWCC) being a crucial component. Most existing unsaturated soil seepage models are established based on the static soil-water characteristic curve model. However, the dynamic capillary pressure has been observed in experiments conducted in previous studies. In this study, experiments were performed to explore the dynamic impact of the SWCC. The influence of different infiltration rates was studied, and a rate-dependent SWCC model under dynamic conditions was established. The model was validated through experiments. The behavior of an unsaturated soil slope under different rainfall intensities was analyzed based on the equivalent model. The equation for the slope safety factor was then derived using the Bishop method. The slope safety factors based on both the rate-independent and rate-dependent SWCC models were compared. The results indicated that the safety factor continuously decreased with increasing rainfall intensity. The dynamic effect reduced the safety factor, making the slope more susceptible to instability.

Effect of Alstonia Angustiloba tree moisture absorption on the stabilization of unsaturated residual soil slope

Effect of Alstonia Angustiloba tree moisture absorption on the stabilization of unsaturated residual soil slope

Efficient numerical implementation of limit equilibrium method for stability analysis of unsaturated soil slopes using Gaussian integral

Unsaturated soil is widely distributed around the world but less considered in design due to the absence of a convenient analysis method in practice. The Morgenstern–Price (MP) method incorporating the extended Mohr–Coulomb shear strength equation provides a reliable approach to evaluate slope stability in such conditions. However, this method is time-consuming due to the need for a tedious trial-and-error process in determining the scaling factor, which involves complex iterations during each trial. Furthermore, since the relatively complicated nature of unsaturated soil, a dense slice division is necessary to obtain reliable results, making the analysis even more cumbersome. In this paper, an improved MP method for unsaturated soil slope stability analysis is presented, which eliminates the need for a dense slice mesh by employing only a few strategically placed Gauss points along the slip surface. Moreover, the trial-and-error process for determining the scaling factor with the corresponding complex iterations is replaced by an efficient search algorithm with a more concise iteration process, resulting in a more convenient implementation of the proposed method. Extensive examples are provided to validate the effectiveness of the proposed improved MP method, indicating its potential as an accurate and efficient analysis method for unsaturated soil slopes in practical application and relative study involving repetitive analyses.

Slope Stability Analysis Based on the Explicit Smoothed Particle Finite Element Method

A landslide is a common natural disaster that causes environmental damage, casualties and economic losses, which seriously affects the sustainable development of society. In geomechanics, it is one of the largest deformation problems. Herein, the GPU-accelerated explicit smoothed particle finite element method (eSPFEM) for large deformation analysis in geomechanics was developed on the CUDA platform based on high-performance computing using a self-designed eSPFEM program code. The eSPFEM combines the strain smoothing nodal integration techniques found in the particle finite element method (PFEM) framework, which allows for the use of low-order triangular elements without volume locking and avoids frequent information transfer and mapping errors between Gaussian points and particles in PFEM. A numerical simulation of slope instability using the eSPFEM and based on a strength reduction technique was conducted using various examples, including a cohesive homogeneous slope, a non-cohesive homogeneous slope, a non-homogeneous slope and a slope with a thin soft band. The calculation results show that the eSPFEM can be applied to slope stability analysis under different working conditions, simulating the entire process of slope instability initiation, sliding and reaccumulation, and obtaining reliable FOS values. A numerical simulation was conducted to analyse a landslide that occurred in the Zhangjiazhuang tunnel on the Lanzhou–Xinjiang high-speed railway line on 18 January 2016. A natural unsaturated soil slope, a soil slope with a high moisture content and a soil slope with a high moisture content subjected to an earthquake were analysed. The findings of this study are in good agreement with the actual slope failure conditions. The primary triggers identified for the landslide were heavy rainfall and earthquakes. The verification results indicate that the eSPFEM can effectively simulate an actual landslide case, showcasing high accuracy and applicability in simulating the large deformation behaviour of landslides.

A comparative study of critical failure surface in unsaturated soil slopes

Landslides are rapid downslope movements triggered by factors such as rainfall, earthquakes, or human activity, where factors like relative permeability, air flow, and variations in hydraulic conductivity affect the mechanisms behind rainfall infiltration and landslide occurrence. This study investigates these phenomena using the finite difference method (FDM) and finite element method (FEM) in FLAC and PLAXIS software. These methods account for the coexistence of water and air, including the Two-phase flow option, in evaluating unsaturated slope stability and identifying critical failure surfaces. The efficiency of these approaches is gauged by varying soil parameters and exploring the impact of different values of suction and hydraulic conductivity, as well as soil-water characteristics, on the safety factor. It was observed that there are disparities between both software packages at high suction values, which impact the safety factor. FLAC is noted for its conservative approach and superiority in representing unfavourable conditions.

Effect evaluation of grass on shallow stability of unsaturated volcanic soil slope in seasonal cold region

Effect evaluation of grass on shallow stability of unsaturated volcanic soil slope in seasonal cold region

Stability analysis of unsaturated soil slopes with cracks under rainfall infiltration conditions

Pre-existing (open) cracks at slope crests, especially tension cracks, are a significant factor in the transition from shallow to deep-seated landslides in unsaturated soil slopes induced by rainfall. This paper presents an analytical framework to assess the stability of unsaturated soil slopes for deep-seated rotational failure considering arbitrary crack depths and unsteady infiltration, and its effectiveness is verified by previous literature and finite element analysis. A closed-form formula is proposed for the maximum depth of cracks in unsaturated soils by the stability of the vertical crack boundary. A parametric study is performed to investigate the impact of some key parameters on the stability of unsaturated soil slopes with cracks. Dimensionless stability charts are developed, which can calculate the factor of safety for the slopes with cracksof any depth and can reflect that the potential slip surfaces through or without passing through the crack tip. In addition, given the existence of a critical crack depth and maximum crack depth, with a ratio ranging from 0.5 to 0.6 based on the stability charts, deep-seated rotational failure is more likely to occur than failure caused by a crack boundary.

Stability of unsaturated soil slope considering stratigraphic uncertainty and rotated anisotropy of soil properties

AbstractThe stratigraphic uncertainty and rotated anisotropy of soil properties exist widely in nature. Recent studies have shown that the slope stability was significantly influenced by these two uncertainties. However, there is no proper method for simulating these two uncertainties at the same time, and the influence of the two uncertainties has not been considered in previous unsaturated soil slope stability analysis. This paper aims to propose a coupled method for characterizing the stratigraphic uncertainty and rotated anisotropy of soil properties, and investigate the unsaturated soil slope stability considering the two uncertainties. Through a slope case, the proposed method for characterizing the two uncertainties is examined. The effect of rotational angle on the slope stability and groundwater table is studied. In addition, four different uncertainty considerations are chosen to compare their influence on the slope stability and groundwater table. The results show that the proposed method can well characterize the two uncertainties at the same time. The rotational anisotropy of soil properties has a substantial impact on the slope stability and groundwater table. The rotational angles corresponding to the maximum and minimum reliability index of slope depend on the uncertainty considerations in the slope stability analysis. The slope reliability index only considering stratigraphic uncertainty is the highest, and the slope reliability index considering stratigraphic uncertainty and rotated anisotropy of soil properties is the lowest.

Numerical modeling of small-scale unsaturated soil slope subjected to transient rainfall

Numerical modeling of small-scale unsaturated soil slope subjected to transient rainfall

Exploring the stability of unsaturated soil slope under rainfall infiltration conditions: A study based on multivariate interrelated random fields using R-vine copula

Estimating the instability of soil slopes due to rainfall in highly heterogeneous materials poses a considerable challenge. In this study, a general framework for coupled hydro-mechanical modeling of rainfall-induced instability in unsaturated slopes with multivariate random fields is developed. The R-vine copula is introduced to simulate the intricate non-Gaussian dependencies between soil parameters. UMAP is utilized for visualizing these dependencies. The study compares the fitting performances of R-vine and Gaussian copulas using LOWESS Regression. Subsequently, deterministic model computations are conducted in Abaqus, along with batch random field model analysis based on the R-vine copula. The instability probability of soil slopes under rainfall infiltration conditions is evaluated through direct Monte Carlo simulations, and statistically investigate the relationships between groundwater level, sliding volume, plastic zone volume, and safety factor. The findings indicate that: 1) The R-vine copula model proficiently captures the non-Gaussian dependencies in soil data, demonstrating superior fitting performance over the Gaussian copula; 2) deterministic simulations might overestimate the safety factor at certain instances; 3) as rainfall progresses, a growing negative correlation is observed between groundwater levels and slope instability; 4) continuous rainfall leads to a re-equilibration of the sliding mass, heightening the influence of the sliding volume on stability.

Upper-bound optimized solution of unsaturated soil slope stability under steady and unsteady flows

The increasing frequency of extreme weather events is leading to a rise in unsaturated soil slope instability near the earth's surface year by year. Establishing the method for analyzing slope stability under complicated hydrological conditions is imperative. This study proposes an approach that combines finite element (FE) seepage analysis with upper-bound limit analysis to evaluate the stability of unsaturated soil slopes. Two kinematically failure mechanisms are constructed based on the spatial discretization technique via point by point including the rotational and rotational-translational combinational failure modes, which can adapt to the complex pore water pressure distribution and varying soil unit weight. Additionally, a novel optimized solution scheme that integrates dichotomy and meta-heuristic optimization approaches is adopted to determine the factor of safety (FoS) and critical slip surface of slopes. The effectiveness and practicality of this method are validated by comparing with the published examples of slope stability evaluation under horizontal and inclined water table. Moreover, the variation of failure mode during the rainfall infiltration is illustrated by a case study of the slope under heavy rainfall. The methodological framework presented in this study can provide a basis for evaluating the stability of saturated–unsaturated soil slopes with 2D seepage conditions.

Kinematical Analysis of 3D Seismic Stability of Slopes in Unsaturated and Inhomogeneous Soils Using a Pseudodynamic Method

Kinematical Analysis of 3D Seismic Stability of Slopes in Unsaturated and Inhomogeneous Soils Using a Pseudodynamic Method

Experimental Investigation on Shear Behavior of Partially Saturated Silty Soil under Constant Water Content and Constant Void Ratio Conditions

Abstract Matric suction is a crucial parameter that affects how unsaturated soils behave in terms of shear strength. Understanding it is essential for solving geotechnical problems like the stability of unsaturated soil slopes, foundations, embankments, and retaining walls. To investigate the shear behavior in unsaturated soil, a double cell triaxial test apparatus is used in the current research to carry out a series of triaxial compression tests under constant water content and constant void ratio conditions. Samples of silty soil, named DL-clay, were prepared with three different degrees of compaction: 80 %, 83 %, and 86 %, and water contents of 20 % (optimum water content) and 25 %. The soil samples were consolidated isotropically under net confining pressures of 300 kPa and 500 kPa before being sheared with constant volume. In another series of tests, water was infiltrated into the sample at 0 kPa deviatoric stress before the start of shearing with constant volume. Some specimens were also sheared with constant confining pressure for comparison purposes. From the test results, it is ascertained that maintaining a constant volume, i.e., constant void ratio during shearing, gives contour-like trajectories that can aid in defining the state boundary surface of unsaturated soil. It was also observed that within the axial strain range of 0–2 %, there was unusual behavior of a temporary sudden dip in the axial stress, which was more perceivable for samples having a high value of initial matric suction.