Stability Of Reinforced Slopes Research Articles

Application of material point method in modeling soil-geosynthetics interactions-a literature survey

The material point method (MPM) has garnered significant attention in recent years owing to its advantages in solving soil–water-structure interaction problems involving large deformations in geotechnical engineering. The MPM combines the benefits of point-based and mesh-based approaches (finite element method) with both Eulerian computational mesh and continuum descriptions of materials. The successful integration of MPM in simulated landslides, internal erosion, and excavation has been frequently reported. However, solving the soil–geosynthetic interaction problem with the MPM has not been explored, although such problems often entail large deformations. The goal of this study is to collate studies on the simulation of geosynthetics and their interactions with soil using MPM. This paper first discusses the basics of MPM and the formation of thin membrane materials using MPM. It also includes limited applications of MPM in simulating soil–geosynthetic interactions. The applications demonstrate that the MPM is particularly effective in resolving large deformation problems associated with geosynthetics, including problems of landfill settlement, reinforced-slope stability, and geocontainer dropping.

Probabilistic pile reinforced slope stability analysis using load transfer factor considering anisotropy of soil cohesion

AbstractA probabilistic limit equilibrium framework combining empirical load transfer factor and anisotropy of soil cohesion is developed to conduct pile‐reinforced slope reliability analysis. The anisotropy of soil cohesion is determined conditioned on that the thrust force direction is parallel to the major principal direction and it is easily combined with load transfer factor, which are related with soil parameters, and pile parameters. The proposed method is illustrated against a homogeneous soil slope. The sensitivity studies of pile parameters on factor of safety (FS; calculated at respective means of soil parameters) and β demonstrated that the anisotropy of soil cohesion tends to pose significant effect on reliability index β than on FS. The effect of anisotropy of soil cohesion on FS is found to be slightly different under different pile locations, whereas its effect on β is observed to be least if piles are drilled at the middle part of slope and more significant effect is observed when piles are drilled at the lower and upper part of slope. The plots from the sensitivity studies provide an alternative tool for pile designs aiming at the target reliability index β. The proposed method contributes to the pile‐reinforced slope stability within limit equilibrium framework.

Temperature effect on the stability of 3D reinforced slopes under unsaturated flow conditions

Slopes are increasingly exposed to elevated temperatures owing to extreme climates or human activities, such as droughts, heat waves, and shallow geothermal technologies. This phenomenon has worsened with global warming. However, the influence of temperature changes on slope stability has not been fully investigated from the perspective of safety. This study introduces an analytical framework for calculating the safety of three-dimensional reinforced slopes which considers the effects of temperature changes and different unsaturated flow conditions. With temperatures ranging from 10 °C to 40 °C, the matric suction of unsaturated soil is thermally sensitive, which causes change in the shear strength of unsaturated soil. To incorporate the temperature effect into the reinforced slope stability assessment, the temperature dependence of the apparent cohesion of unsaturated soil was quantified using a temperature-related effective stress model and soil–water characteristic curves. Thus, the safety factors and reinforcement strength of the slopes were deduced based on the upper-bound theorem of limit analysis. For validation, the proposed method was compared to two previously reported analytical methods, and its effectiveness was further verified through numerical simulations. Finally, the temperature effect was fully investigated and discussed by performing a series of parametric analyses, and suggestions were provided for practical engineering reference.

First order reliability-based design optimization of 3D pile-reinforced slopes with Pareto optimality

As verified structures for landslide mitigation, stabilizing piles are often adopted to treat local failure zones of width-limited soil slopes. To achieve a balance between slope safety and construction cost, an optimized piling scheme for treating width-limited soil slopes should be obtained through three-dimension (3D) stability analysis. In this regard, this paper presents a novel calculation framework for the multi-objective optimization (MOO) design of stabilizing piles. It is based on the first-order reliability method (FORM) and considers a 3D width-limited slope failure with geological uncertainties. The study first develops a deterministic 3D stability model of pile-reinforced slopes using limit analysis. Accounting for soil shear strength uncertainties, reliability analyses of 3D reinforced slopes are conducted based on the prescribed pile-reinforcement patterns. Then, a multi-objective probabilistic design procedure combining the Pareto front and reliability analysis results is proposed. The effectiveness and significance of the proposed MOO design framework are demonstrated through two illustrative examples: one involves designing stabilizing piles in a homogenous slope, and the other involves designing for an inhomogeneous earth slope with depth-dependent soil cohesion. To gain better understanding of the probabilistic impact of uncertain pile design parameters on reinforced slope stability, comprehensive parametric studies are conducted.

Component reliability and sensitivity analysis of anchor-pile-wall reinforcement design of a multilayer soil slope

Component reliability and sensitivity analysis of soil-slope combined-reinforcement deterministic designs are studied using a hybrid numerical-probabilistic method. Major components are qualitatively identified with numerical simulations to avoid redundancy evaluations. Quadratic polynomials as response surfaces are stepwise regressed to predict component load effects. Major component resistances of supporting structures are calculated in states of soil ultimate equilibrium and maximum allowable deformations obtained according to building and foundation types. Component performance functions (PFs) are established based on component failure models and soil-mass deformation properties. Reinforced slope stability reliabilities are calculated with first-order second-moment and design point methods. The reinforcement probability safety indicated by component reliability indices is adopted to check whether the deterministic design needs improvement. This methodology is applied to a loess slope reinforced by combined supporting. The resultant reliability indices of the slope imply some improving treatments should be made. Sensitivity analysis shows some variable variation has a more significant impact on the PFs; inversely signed sensitivity coefficients indicate that the equilibrium point between PFs should be considered when modifying parameters. Stable monitoring results of modified design implementation indicate that probabilistic analysis of component stability is necessary for some slope-treatment designs with distinct probability distribution variables.

Reliability-based monitoring sensitivity analysis for reinforced slopes using BUS and subset simulation methods

Slopes are frequently stabilized by reinforcement measures in geological and geotechnical engineering. Effectiveness of reinforcement measures is vital to slope failure risk mitigation, but it is affected by geological and geotechnical uncertainties arising from loads, geological formations and geotechnical properties. In face with these uncertainties, slope reinforcement measures are often monitored at site, and monitoring variables that are sensitive to the safety and reliability of the reinforced slope stability shall be carefully selected during monitoring design, which highly depends on engineering experience and judgments (i.e., prior knowledge). How to exercise the prior knowledge in a quantitative and transparent way in geotechnical monitoring design remains unexplored. This can be accomplished using reliability-based monitoring sensitivity analysis, which requires significant computational costs due to repeated inverse analyses and reliability analyses given different possible values of monitoring variables. This paper develops an efficient reliability-based monitoring sensitivity analysis framework based on BUS (i.e., Bayesian updating with structural reliability methods) with Subset Simulation methods. The proposed approach is illustrated using a real reinforced slope example. Results show that it quantifies reliability sensitivity of different monitoring variables (e.g., displacements at different locations on slope surface) in a cost-effective manner based on prior knowledge. Such reliability sensitivity information facilitates decision-making in selecting sensitive monitoring variables during the monitoring design of reinforced slopes.

Numerical Investigation of Slope Stabilization Using Recycled Plastic Pins in Yazoo Clay

Geographically, at the center of Mississippi is a concentration of High Plastic Yazoo Clay Soil (HPYCS). Shallow landslides frequently occur in embankments constructed with HPYCS caused by rainfall-induced saturation of the embankment slope. The traditional methods are becoming expensive to repair the shallow slope failure. The use of Recycled Plastic Pins (RPPs) to stabilize shallow slope failures offers a significant cost and construction benefit and can be a useful remedial measure for these types of failures. The current study investigates the effectiveness of RPP in slopes constructed with HPYCS, using the Finite Element Method (FEM). The FEM analysis was conducted with the PLAXIS 2D software package. Three uniform and varied RPP spacings were investigated to reinforce 2–4H:1V slopes. Reinforced slope stability analyses were performed to investigate the applicability of RPP in HPYCS. The FEM analysis results indicated that RPP provides shear resistance for the sloping embankment constructed of HPYCS. Uniform spacing of RPP provides sufficient resistance that increases the Factor of Safety (FS) to 1.68 in 2H:1V slopes with deformation of RPP less than 15 mm. The uniform spacing and varied spacing combination of RPP increase the FS to 2.0 with the deformation of RPP less 7 mm.

Assessment of the Reinforced Slope Stability Under Earthquake Loading

Failure of the soil slopes by dynamic excitation is one of the most vital geotechnical earthquake hazards which may lead to serious destruction to the bridge abutments, dams, embankment, and structures resting on the slope. Moreover, due to deficient space available for the construction of slopes in urban areas, high and steep slope is constructed by geotextile reinforcement slopes. In this study, numerical modelling is made to study the behaviour of soil slope reinforced by geotextile under earthquake loading using the finite element method available in, optumG2. The value of the factor of safety (FOS) for unreinforced soil slope is calculated using the strength reduction method (SRM) at slope angle (β = 60°) and the height of the slope is 10 m. In the unreinforced slope, a critical failure surface was obtained due to which slope is reinforced with geotextile under static and earthquake loading. Furthermore, a parametric analysis is carried out to evaluate the effect on different lengths of geotextile and different vertical spacing for the stability of reinforced slope with horizontal ground acceleration coefficient (0.1-0.4). From the outcomes of the present study, it is noted that a stable slope can be achieved with an optimized configuration of the reinforcement under seismic loading, also a steeper slope can be achieved using reinforcement compared to that of an unreinforced slope.

Upper Bound Analysis of 3D-Reinforced Slope Stability Subjected to Pore-Water Pressure

AbstractPore-water pressure is a universal unfavorable external force and often poses an adverse impact on reinforced slope stability. Although recently the stability assessment of reinforced slope...

STABILITY ANALYSIS OF STRIP FOOTING ON REINFORCED SAND SLOPES

This paper presents a total of 55 runs using Slide v6 software computer program to study the stability of axially loaded strip footing located near the crest of sand slope model without or with geogrid reinforcement. The model represents an application of reinforced earth technique for foundations located on sloped embankments that behave as supports for retaining walls or bridge abutments. The parameters investigated were slope inclination , footing distance from edge of the slope b, length and number of geogrid layers  and N, type of geogrid reinforcement in terms of its structure, polymer type, yield elongation % and strength, vertical spacing between geogrid layers  and depth of embedment of footing . The limit equilibrium analysis results show that (i) Slide v6 software program is efficient to study unreinforced or reinforced slope stability problems both for research or design purposes, (ii) Use of geogrid reinforcement would increase both slope stability and safety. The major benefit was obtained when reinforcing layers number N equal to four each of length 10B where (B = width of footing), (iii) SS30 geogrid is more effective for reinforcing slopes than TT045 type due to its higher pullout strength and other properties such as structure, shape, rib profile and grid junction tensile strength that affecting soil/grid interlock, and (iv) the optimum depth of the upper most layer of reinforcement was u = 0.5B whereas the optimum vertical spacing of the reinforcement layers  lies in the range of 0.50B - 0.75B.

Simple Model on Water Retention and Permeability in Soil Mixed with Lignocellulose Fibres

Natural or lignocellulose fibres have been widely used for reinforcing soils in geotechnical infrastructures by using their mechanical reinforcement. However, less attention has been taken to the hydraulic properties of soil-lignocellulose fibre composites, namely Soil Water Retention Curve (SWRC) and soil water permeability. These hydraulic properties are the key parameters when conducting transient seepage analysis in reinforced slope stability calculation. Till now, there is no model yet that can capture SWRC and water permeability of soil-lignocellulose fibre composite. This technical note aims to develop a new and simple model for predicting the SWRC and water permeability of soils mixed with lignocellulose fibres. The model considers the void ratio change by incorporating the air void from fibres. The void ratio function is then fed into a void-ratio-dependent SWRC model. SWRCs and water permeability of soils mixed with two lignocellulose fibres (jute and coir) were measured systematically to provide high quality data to validate the proposed model. There were three replicates for each case. It shows that the presence of pore structures in natural fibres reduced air entry value of soils from 8 kPa to 2–3 kPa, while it had no effects on desorption rates. Moreover, those pores in lignocellulose fibres increased the water flow path, resulting in increased water permeability. As demonstrated by dye tracer experiments, the increased water flow was along the cellulose, hemicellulose fibrils inside the fibre and soil-fibre interface. The comparisons between experimental measurements and model predictions indicate that the proposed simple model can capture the effects of natural fibres on soil hydraulic properties quite well, with the maximum discrepancy less than 15% and 28% for SWRC and water permeability, respectively.

Closure to “Limit-Equilibrium Method for Reinforced Slope Stability and Optimum Design of Antislide Micropile Parameters” by Deng Dong-ping, Li Liang, and Zhao Lian-heng

Closure to “Limit-Equilibrium Method for Reinforced Slope Stability and Optimum Design of Antislide Micropile Parameters” by Deng Dong-ping, Li Liang, and Zhao Lian-heng

Discussion of “Limit-Equilibrium Method for Reinforced Slope Stability and Optimum Design of Antislide Micropile Parameters” by Deng Dong-ping, Li Liang, and Zhao Lian-heng

Discussion of “Limit-Equilibrium Method for Reinforced Slope Stability and Optimum Design of Antislide Micropile Parameters” by Deng Dong-ping, Li Liang, and Zhao Lian-heng

Analysis of a Nailed Soil Slope Using Limit Equilibrium and Finite Element Methods

This paper aims at the two most common methods used for slope stability analysis. An attempt has been made to bring out the differences in results of reinforced slope stability analysis obtained from SLOPE/W (limit equilibrium based) and PLAXIS 2D (finite element based). The analysis is carried out on two slope angles of 45° and 60°, which are reinforced with nails at three different inclinations of 0°, 15° and 30° respectively. Both the slope angles and all nail inclinations are taken from the horizontal. A comparative study on stability parameters such as factor of safety, critical slip surfaces and nail forces has been carried out. The limit equilibrium method is found to yield higher values of factor of safety in comparison to finite element method. The failure surfaces from both methods are found to vary significantly. Large nail forces are observed by limit equilibrium method for 45° slope with all nail inclinations, whereas for 60° slope angle, finite element method shows an increase in the nail forces. The effect of other parameters like bond length in limit equilibrium, soil–nail interaction and bending stiffness in finite element are also studied.

To A Probabilistic Approach of Reinforced Slope Stability Analysis

A developed probabilistic model to analyze reinforced slopes is presented in this paper where, a log-normal distribution law and a first order of second moment method FOSM are used. Moreover, an interactive code, using C ++ language, based on a developed model, is carried out. With idea to validate the developed model, a parametric study was conducted, considering three types of current soils, taking into account the following parameters: cohesion ''C'', internal friction angle ''φ '', the unit weight ''γ'' and apparent soil-reinforcement friction angle ''α''. Expected variables were: reliability index ''  '', the probability of failure (ruin) Pr'' and the safety factor '' FS. Obtained results show that the friction angle φ and cohesion C seem most significant while, the reinforced soil unit weight ''γ'' and the soil-reinforcement interface friction angle ''α'' show a slightly sensitive influence. Besides, it is clearly showed that safety factor increases with the increase of reinforcement length.

Stability Analysis of Reinforced Slopes Using Upper Bound Limit Analysis Method

The kinematic method of limit analysis approach is applied to study stability of reinforced slopes. The amount and length of reinforcement required to prevent the slope to collapse are determined based on different mechanisms. A new method consisting of horizontal blocks is used in translational mechanism. The failure wedge is divided into a number of horizontal slices involving reinforcements. The reinforcements do not intersect the slices. Thus, they have no direct influence on the inter-slice forces. The presented method can reduce difficulties of stability analysis for reinforced slopes. In this paper, the seismic stability of slopes reinforced with geosynthetics is investigated. The seismic analysis procedure is substituted with pseudo-static horizontal forces. While such an approach ignores the acceleration history of a structure, it is routinely used in practice. It has been assumed that the geosynthetics are uniformly distributed in the height of slope. Based on these assumptions, different possible failure mechanisms are considered and necessary analytical expressions for determining the design parameters are derived for each mechanism. The results of these analyses are presented to illustrate the influence of different parameters such as geometrical parameters of slopes, soil characteristics, and seismic forces on the stability of reinforced earth structures.

Application Evaluation of Countermeasure Method using Analysis of Failure Causes for Reinforced Slope

This paper described that the failure causes of reinforced slope are analyzed based on the effect of geological and rainfall. The analysis result confirmed that the rainfall has effects on the stability of reinforced slope. Therefore, it was applied to the dewatering method using collector well for slope stabilized, and then the analysis of seepage and slope stability were conducted on slope with the applied method. The results of seepage analysis are corresponded with failure cause by rainfall and the results of slope stability, which is applied to dewatering method, are satisfied with safety factor criterion. Therefore, it confirmed that the dewatering method using collector could be possible to apply in field and reasonable method for slope stabilized during heavy rainfall.

地山補強土工法の補強機構と変形拘束効果

Conventional design method for soil nailing is based on the effects of tensile force developed in reinforcement installed in cut slope. As the tensile force is affected by the deformation of reinforced slope, the approach of the design method should be on the basis of the allowable deformation. On the other hand, it is said that the restraint effect in reinforced zone is more effective for reinforced slope stability under conditions of small allowable deformation. However, even the definition of the restraint effect for bar of reinforcement is still not clear. In this study, the reinforcement mechanism of restraint effect is investigated by distinct element method firstly, and secondly the effect of the interval of reinforcements on the development of restraint effect is examined by finite element method. Finally, it concludes that the design method of considering the restraint effect is effective to the reinforcement of high priority structure as a cut slope in important road system.

鉄筋類挿入工法の補強機構と設計法に関する考察

Soil nailing is a typical method for earth reinforcement that is widely applicable to both natural and cut slopes. Basically, it is considered to increase slope stability through the tensile force resistance generated in the reinforcement materials. On the other hand, the restraint effect in reinforced zone is effective for reinforced slope stability under the condition that small allowable deformation is adopted. In this study, the mechanism of restraint effect for reinforcement bar in granular soil is investigated by experiment of base friction model and numerical analysis of distinct element method.

Variational displacement method for geosynthetically reinforced slope stability analysis: I. Local stability

This, and a companion paper ( Lemonnier et al., 1998), present a theoretical model, allowing the assessment of the safety factor of a geosynthetically reinforced slope. The present paper deals with the local stability problem, that is the determination of tension and strain distributions in the reinforcements. The global stability analysis of the reinforced slope, which includes this local stability analysis for each sheet of reinforcement, is described in the companion paper. As an improvement of the French ‘displacement method’, ( Gourc et al., 1986), the present theoretical model for the local stability analysis is based on the anchored membrane concept. Its originality is the use of the variational calculus applied to the equilibrium of the membrane. It allows the determination of the optimal shape of the membrane, which gives the minimal tension at the failure surface. This optimal shape has been found to be a log-spiral. A numerical study shows the influence of several geometrical parameters on the determination of the reinforcement tension. Finally, a case history comparison involving results obtained from six current design methods is presented and discussed.