Multi-layered Slope Research Articles

Numerical Modeling of Hydrological Mechanisms and Instability for Multi-Layered Slopes

The process of rainwater infiltration into unsaturated multi-layered slopes is complex, making it extremely difficult to accurately predict slope behaviors. The hydrological mechanisms in multi-layered slopes could be significantly influenced by the varying hydraulic characteristics of different soils, thus influencing slope stability. A numerical model based on Hydrus 2D was constructed to investigate the hydrological mechanisms of multi-layered slopes under different slope inclinations and rainfall intensities. The results revealed hydraulic processes in response to rainfall in unsaturated multi-layered slopes, in which layered soils retard the advance of wetting fronts and affect seepage paths in the slope. The results also showed the characteristics of hydraulic parameters, including pore water pressure and moisture content, under different conditions, and explained the crucial factors at play in maintaining slope stability.

Profiles of suction stress of layered soils under infiltration conditions and its applications

Suction stress is critical for understanding the hydrological and mechanical behavior of unsaturated soils in construction and engineering. Many soils encountered in these fields exhibit layering due to geological sedimentation or artificial reinforcement. This study establishes the vertical distributions of matric suction and degree of saturation for layered soils under one-dimensional (1D) steady-state seepage, using the Darcy law and constitutive relationships of unsaturated soils. A closed-form suction stress is derived for an arbitrary number of layers and soil types. Hypothetical layered soils with varying hydraulic properties at four infiltration rates are assessed. Results show that soil stratification affects the suction stress profiles, with the impact depending on infiltration rates, soil configuration, and layer thickness. Abrupt variations in suction stress occur at most layered interfaces due to differences in permeability between adjacent layers. The suction stress profiles can be used to evaluate the earth pressure and stability of layered slopes under seepage conditions. Several case studies of multi-layered slope failures in Southern Italy are presented to demonstrate the suitability of the proposed framework for evaluating the stability of layered slopes under rainfall conditions.

Upper-Bound Limit Analysis of the Multi-Layer Slope Stability and Failure Mode Based on Generalized Horizontal Slice Method

Upper-Bound Limit Analysis of the Multi-Layer Slope Stability and Failure Mode Based on Generalized Horizontal Slice Method

Stability factor prediction of multilayer slope using three-dimensional convolutional neural network based on digital twin and prior knowledge data

Stability factor prediction of multilayer slope using three-dimensional convolutional neural network based on digital twin and prior knowledge data

Stability Analysis of a Multi-Layered Slope in an Open Pit Mine

The design of slopes in open pit mines requires an in-depth understanding of the ground behavior to predict the potential failure mechanism and to better determine the stabilization measures. This study compares the critical slip surface defined by the limit equilibrium method (LEM), the limit analysis (LA), and the finite elements method (FEM) for the stability analysis to better approach the stability on a multi-layered slope. The safety factor, the size, and the location of the critical slip surface obtained from the applied methods are considered in the comparisons. This study highlights some features that affect the slope stability and presents a procedure for addressing the evaluation challenges in a multi-layered formation. Moreover, it presents some aspects of the upper-bound computation on the safety factor of a layered slope subjected to the effects of pore water pressures. Based on the obtained results, the critical slip surface defined by the limit equilibrium method compares well with the slip mechanism suggested by the limit analysis and the finite element approach. In view of the differences in the shape and location of the critical slip surface, as well as the values obtained for the safety factor, it is recommended that an engineer should analyze critical slopes using the finite element method in combination with the limit equilibrium or limit analysis method as a cross reference. The authors propose that in defining the potential failure mass, consideration must be given to the conducted field research and monitoring.

Upper Limit Analysis for the Ultimate Bearing Capacity of a Multilayer Slope with Horizontal Stratification

The ultimate bearing capacity is one of the most important mechanical parameters in the mining and geotechnical fields and has a vital influence on the stability of slopes and the safety of constructions and structures. The determination of the ultimate bearing capacity has become a controversial issue in slope engineering. This study proposes a way to obtain the ultimate bearing capacity of a multilayer slope with horizontal stratification. According to limit analysis theory, three typical multiblock sliding failure modes for a multilayer slope with horizontal stratification are established. The upper limit solution of the ultimate bearing capacity of a multilayer slope, considering the influence of horizontal stratification, is derived. The optimization procedure is carried out to obtain the optimal value of the ultimate bearing capacity by using the sequential quadratic programming algorithm. The accuracy of the present method is proven based on a comparison of calculation results using other analytical methods and the numerical simulation method. The influence analysis of the parameters, involving the slope angle, soil strength, and distance of the foundation from the slope shoulder, is performed. The results indicate that the error between the calculated results of the present method and those of numerical simulation, as well as the error between the calculated results of the present method and those of other existing methods, is less than 10%. The ultimate bearing capacity linearly decreases with increasing slope angle, while it linearly increases with increasing distance of the foundation from the slope shoulder. The analytical method provides a method to analyze the ultimate bearing capacity of a multilayer slope, which effectively solves the problem of heterogeneity of soil layers observed in the natural slope. The results from this study can be used as a guide to estimate the stability of the slope and design of the foundation on a slope considering the load action near the slope.

Seismic Behavior Analysis of the Bank Slope Considering the Effect of Earthquake-Induced Excess Pore Water Pressure

Soil slopes, located near rivers or the sea, often get damaged dramatically under seismic action due to the high groundwater level. To determine the failure mechanism, this study proposed an analytical method for a composite critical slip surface of a multi-layer slope considering the effects of the excess pore water pressure using the Newmark’s method and variational principle. Based on this, a method for evaluating the effects of the excess pore water pressure on the permanent displacement of the slope under seismic action was established, and influence mechanisms of the excess pore water pressure on failure modes of the multi-layer bank slope at different groundwater levels were studied. The research results show that slip surfaces basically have same shapes at different groundwater levels; however, with the rise of the groundwater level, soil above a seepage line is not affected by the excess pore water pressure, and its sliding scale slightly changes. For soil below the seepage line influenced by the excess pore water pressure, the slip surface constantly extends to the interior of the slope, resulting in the increase in the sliding scale. Due to the cumulative increase in the excess pore water pressure, the bank slope at different groundwater levels is generally manifested as shear sliding at the slope toe and tensile fracture at the top. Finally, based on the shaking table test, the proposed method was verified to be reasonable and accurate. This research provides a simple and reliable method for slope engineering technicians to evaluate the stability of water-rich soil slopes.

Locating critical slip surfaces of soil slopes with heuristic algorithms: A comparative study

Calculating the minimum safety factor for locating or investigating the critical slip surfaces of soil slopes is a complex optimization problem. In this work, a series of variables are utilized to represent the slip surfaces of the slope, and the Morgenstern and Price's method is used to calculate the safety factor of a given slip surface. The performances of eight heuristic optimization algorithms (grey wolf optimizer, particle swarm optimization algorithm, whale optimization algorithm, salp swarm algorithm, multi-verse optimizer, ant lion optimizer, cuckoo search algorithm, and equilibrium optimizer) for locating the critical slip surfaces of slopes are compared. Three cases (one homogeneous slope and two multi-layered slopes) show that the equilibrium optimizer is superior to the other algorithms in terms of the quality of the solution, the convergence rate, and the robustness. One should carefully use the salp swarm algorithm and ant lion optimizer to locate the critical slip surfaces of slopes.

Influence of Layer Transition Zone on Rainfall-Induced Instability of Multilayered Slope

Abstract Although numerous studies have been paid much attention to rainfall-induced instability of multilayered slopes, the interface between layers is generally considered to be “zero thickness”, and the layer transition zone between layers is neglected. In this study, the influence of the layer transition zone on the rainfall-induced instability of multilayered slope was investigated. A model was developed to simulate the rainfall infiltration process, the distribution of pore water pressure, and the stability of multilayered slope by coupling the unsaturated seepage model and the slope stability analysis method. Based on the analysis of the multilayered slopes with the different thickness ratios of the layer transition zone, a method for determining the critical thickness of the layer transition zone was proposed. The results showed that the layer transition zone had a significant influence on the stability of multilayered slope. It was found that the presence of the layer transition zone in the multilayered slope reduced the hydraulic conductivity of the slope and increased the rate of formation of transient saturated zone, which contributed to excess pore water pressure at the toe of the slope. The analysis of the local factor of safety (LFS) showed that when the thickness ratios of the layer transition zone were between 2.5% and 5%, the corresponding hydraulic conductivity of the slope decreased by 1%-2.5% and the maximum failure area of the slope during the rainfall was 25% of the slope. Our study highlighted the importance of the layer transition zone for the rainfall-induced instability of the multilayered slope.

Research on slope reliability analysis using multi-kernel relevance vector machine and advanced first-order second-moment method

To increase the efficiency and accuracy in slope stability analysis, a reliability analysis method based on machine learning and the advanced first-order second-moment (AFOSM) method was proposed, and the partial derivative of the machine-learning algorithm was derived. First, a multi-kernel was introduced to establish the multi-kernel relevance vector machine (MKRVM). Then, the kernel parameters of the MKRVM were optimized by the harmony search (HS) method to use the high-precision MKRVM method instead of the traditional methods for determining the factor of safety. It was necessary to obtain the partial derivative of the performance function, which was explicitly expressed by the trained MKRVM in this paper. Finally, the AFOSM was adopted to calculate the reliability index of the slope, as the AFOSM was more reliable because the design point was located at the failure surface. With two samples, from a single-layer slope and a multilayer slope, the calculation results show that the MKRVM–AFOSM is easy to use, highly computationally efficient, and reliable.

Smart determination of borehole number and locations for stability analysis of multi-layered slopes using multiple point statistics and information entropy

Subsurface stratigraphy of multi-layered slopes is essential and crucial for slope stability analysis. It is usual practice for engineers to interpret stratigraphic boundaries separating different soil layers using both site investigation data and prior knowledge of local geology, but such practice might encounter significant challenge when the site data are very limited. In addition, uncertainty in stratigraphic boundaries has not been explicitly or quantitatively considered in planning of site investigation (e.g., determination of borehole number and locations). There lacks a quantitative and objective tool to determine the optimal locations and number of boreholes for slope stability analysis while accounting for stratigraphic uncertainty. In this study, a smart sampling strategy based on multiple point statistics and information entropy is proposed for delineation of slope subsurface stratigraphy and planning of geotechnical boreholes. It is a data-driven approach that enables an ensemble of prior knowledge within a training image using multiple point statistics. The proposed method not only provides evolution of the most probable interpolation from sparse measurements and the associated interpolation uncertainties, but also adaptively determines the optimal locations of boreholes. Effectiveness of the proposed method is illustrated and validated through both a simulation example and a real case. It is found that the data-driven framework can automatically identify locations of largest interpolation uncertainty within a multi-layered slope conditional on its outcrops, and that the associated stratigraphic uncertainty gradually reduces as borehole number increases. More importantly, the optimal number and locations of boreholes required for slope stability analysis are adaptively determined by the proposed method.

Sensitivity of the stability assessment of a deep excavation to the material characterisations and analysis methods

Due to the spatial variability of material characterisations in deep and large scale excavations, stability assessment is often a challenging task. Numerous slope stability analysis methods based on a range of assumptions and principles are implemented in commercial software packages to ease the process of stability assessment of non-homogeneous and multi-layered slopes. However, the selection of a suitable method remains crucial as the application of an unrealistic or unsuitable method may lead to catastrophic consequences. Besides material shear strength parameters, and analysis methods, non-strength characterisations such as permeability and creep can affect the result of slope stability analysis significantly. In this study, the sensitivity of the stability assessment of a deep excavation in Australia to material characterisations such as friction angle, cohesion and permeability and creep is investigated by the use of different formulations and assumptions of the Limit Equilibrium Method (LEM) and the Finite Element Method (FEM) as the two most common slope stability methods. The results show that the stability assessment is highly sensitive to the applied method and assumptions. Moreover, the role of material strength and non-strength parameters and the selection of a suitable constitutive model in slope stability assessment is presented.

Physical Model Experiments on Water Infiltration and Failure Modes in Multi-Layered Slopes under Heavy Rainfall

To assess the influence of an intermediate coarse layer on the slope stability during heavy rainfall, knowledge about water movement and how slope failure occurs is important. To clarify the characteristics of water infiltration in a multi-layered slope and assess its influence on the slope failure modes, eight groups of physical slope models were investigated. It was found that the unsaturated hydraulic conductivity in the coarse layer (5.54 × 10−6 cm/s) was much lower than that of the fine layer (1.08 × 10−4 cm/s), which resulted in the capillary barrier working at a lower water content. Intermediate coarse layers embedded between finer ones may initially confine the infiltration within the overlying finer layers, delaying the infiltration and eventually inducing a lateral flow diversion in the inclined slope. Two different failure modes occurred in the model experiments: surface sliding occurred at the toe in the single-layer slope group and piping occurred at the toe in the multi-layered slope as the rainfall water accumulated, was diverted along the interface, and then broke through in the downslope direction of the intermediate coarse layer. The lateral flow diversion caused by the capillary barrier and the tilt angle may be the major factors influencing the difference of the failure modes. The result also revealed that the coarser layers may have negative effects on the slope stability.

Water movement in unsaturated multi-layered slope under heavy rainfall conditions in wetting and dry process

Water movement in unsaturated multi-layered slope under heavy rainfall conditions in wetting and dry process

GPR data interpretation in the landslides and subgrade slope surveys

The paper describes results of GPR survey of multi-layered slopes of transport structures. A brief review of this problem by domestic and foreign researchers is presented. The significance of this work is determined by complexity of GPR data interpretation when the GPR survey is conducted in a common offset or common midpoint mode in case of dipping layers. The typical patterns are obtained, the groups of the same reflection events are picked and possible reasons of them are stated by numerical modeling using GprMax software. The technique of ground velocities finding in case of GPR survey of dipping layers is proposed.

Analytical solutions of pore-water pressure distributions in a vegetated multi-layered slope considering the effects of roots on water permeability

New analytical solutions of pore-water pressure (PWP) distributions in a vegetated multi-layered slope are derived considering the effects of roots on water permeability. PWP distributions are significantly affected by root-induced reductions in water permeability due to increases in the root volume ratio (Rv). Under drying conditions, negative PWP increases with Rv. The negative PWP induced by root water uptake increases with the desaturation coefficient (αi) or the ratio of the transpiration rate to saturated water permeability (Tp/ksi). As the overall water permeability underneath the vegetation layer decreases, the negative PWP induced by root water uptake increases.

Research on the Law of the Infuence on Multilayer Slope Load to the the Different Gradient High Slope Stability

In recent years, domestic superelevation embankment common occurance, This paper uses the finite element strength reduction method, analyzing the stability about high embankment and high embankment multilayer under multilayer load with large-scale finite element analysis software named ANSYS, it is researched on the law of the infuence on multilayer slope load to the the different gradient high embankment stability.

Significance of slope sediments layering on physical characteristics and interflow within the Critical Zone – Examples from the Colorado Front Range, USA

Abstract The subalpine to montane zones within the Critical Zone (CZ) of the Colorado Front Range, USA outside Pleistocene glaciation limits are characterized by the abundance of stratified and multilayered slope deposits exhibiting depths >1 m. Initial luminescence dating for the upper sediment layers in different profiles give last glacial ages ranging between 40 and 12 ka. A periglacial origin by solifluction is hypothesized for these slope deposits, which is corroborated by geomorphic and sedimentologic parameters. The stratified slope sediments have a strong influence on the physical and chemical properties as well as on soil forming processes in the CZ. Examples are provided for the sediment derived contribution of some elements and common clay minerals together and the great importance of slope sediments as barriers and pathways for the interflow that runs in sediment layers are shown.

Seismic Wavefields in Multi-Layered Media Calculated by Hybrid Combination of Boundary Element Method and Thin Layer Finite Element Method. The Case of Two-Dimensional SH-Wavefields.

Two-dimensional SH-wavefields in laterally heterogeneous multi-layered media are calculated by using a hybrid method in which the boundary element method (BEM) is combined with the thin layer finite element method (TLFEM) by matching the boundary conditions on vertical boundaries. The traction operators defined on vertical boundaries are used to match the boundary conditions. The traction operators can be approximately calculated from eigenvalues and eigenfunctions for the multi-layered media, which are obtained by using the TLFEM. This method is efficient to calculate scattering of surface waves in laterally heterogeneous multi-layered media. Scattering of Love waves in multi-layered slope structure is investigated. For the case in which a source is in the shallower side, Love waves mainly propagate in the forward direction. The dispersion of Love waves shows an averaged structure of both sides. For the case in which a source is in the deeper side, the amplitude of scattered waves is large, and scattered body waves and back-scattered Love waves exist.

Seismic Wavefields in Multi-Layered Media Calculated by Hybrid Combination of Boundary Element Method and Thin-Layer Finite Element Method. The Case of Two-Dimensional P-SV-Wavefields.

Two-dimensional P-SV-wavefields in laterally heterogeneous multi-layered media are calculated by using the hybrid combination of the boundary element method (BEM) and the thin-layer finite element method (TLFEM). The BEM can be combined with the TLFEM by matching the boundary conditions on vertical boundaries. Expansion of wavefield into summation of normal modes is used to match the boundary conditions. This method is suitable to calculate propagation of surface waves in laterally heterogeneous multi-layered media. It is easy to treat incident surface waves from distant sources, which is difficult to calculate by other boundary methods. Since this method does not require the assumption of periodic structure, it can be applicable to nonperiodical problems. Wavefields in a multi-layered slope structure are investigated. When a point source is in a thicker layer side, the amplitude of scattered waves is large and backscattered Rayleigh waves exist. When a point source is in a thinner layer side, Rayleigh waves whose dispersion corresponds to that for an averaged structure of both sides mainly propagate in the forward direction.