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Landslides caused by the progressive failure of sensitive clay slopes may cause substantial economic losses and environmental pollution to pipelines. This study utilizes the Karhunen-Loève (K-L) expansion method, the coupled Eulerian-Lagrangian (CEL) method, and the Monte Carlo method to model the large deformation behaviour of slopes with spatial variability. The proposed RCEL-MC framework for joint analysis of extensive deformation-probability statistics of landslide impact on pipelines confirms that the spatial variability clay slope instability failure mechanism, considering the soil softening effect under earthquake action, aligns more closely with real-world scenarios. Furthermore, based on the statistical failure probability of pipelines impacted by landslides, a sensitive clay slope pipeline safety design method is suggested. The research highlights that the random field parameters significantly influence the load-bearing characteristics of pipelines affected by spatially variable slope progressive failure landslides. The uncertainty surrounding the maximum impact force on pipelines notably increases with the rise of the horizontal correlation length and variability coefficient. When accounting for spatial variability, the maximum impact force on landslide pipelines surpasses the deterministic model analysis results by 28-69 %. It is emphasized that the deterministic model analysis, which neglects the spatial variability of soil and the soil softening effect, may seriously underestimate landslide risk. Based on the criteria for pipeline buckling failure and yield failure, it is advised that the safe design parameters for pipelines in practical projects should fall within the intersection of the secure regions defined by the two failure criteria. [ABSTRACT FROM AUTHOR]

Fragility analysis of slopes under rainfall condition express the conditional probabilities of exceeding prescribed slope limit states under a range of rainfall intensities, which is the basic and pivotal procedure in rainfall-triggered landslide risk assessment. Classical fragility analysis methods of slopes always develop fragility curves with the assumption of lognormal distribution. The validation of assuming the shape of fragility curves as lognormal distribution remains a open question in practice. In addition, the existing fragility analysis of slopes under rainfall condition have not dealt with the effect of spatially-variable geo-material parameters. In the present study, a novel fragility analysis methodology is proposed for the construction of non-parametric fragility curves of slopes under rainfall condition, in which the spatially-variable soil properties are taken into account. The non-parametric fragility curves are developed by the calculated slope failure probabilities under various rainfall intensities on the basis of probability density evolution theory, without restricting fragility functions to some assumed distribution models. With the proposed method and a set of probabilistic slope rainfall seepage and stability analyses, non-parametric fragility curves, fragility surface using two rainfall intensity measures and time-dependent fragility curves of a slope subjected to various rainfall scenarios are obtained for rainfall-triggered landslides risk assessment. [ABSTRACT FROM AUTHOR]

Currently, with the increase in the number of climate anomalies, the frequency and severity of landslides and slope failure events are gradually escalating. Therefore, it is imperative to develop a reliable approach that can assess the evolution of slope stability under the long-term climate effects. This study proposes a feasible framework for the approach. Firstly, a finite element (FE) numerical model that integrates thermal–hydraulic (TH) coupling analysis and land–atmosphere interaction process is established. Particularly, a new algorithm for dealing with the unilateral boundary condition of evaporation and infiltration has been proposed. Secondly, a method combining the numerical simulation with discretization-based upper-bound limit analysis approach is employed to evaluate the slope stability. Finally, the performance of the proposed scheme is tested by tracking the evolution of a cut slope stability under climate influence. Results of the case study suggest that significant variation in equivalent pore fluid pressure (EPFP) with suction is crucial for the stability of unsaturated soil slopes. EPFP is strongly dependent on seasonal climate change. Moreover, the stability analysis method adopted can effectively capture the transformation of slope failure modes. [ABSTRACT FROM AUTHOR]

The temporal patterns of rainfall intensity, characterized by the variability of rainfall intensity over time during a single rainfall event, play a crucial role in landslide triggering and evolution. However, the influence of temporal patterns of rainfall intensity on the fragility and reliability assessment of slope instability has received limited attention. This study presents a novel methodology for probabilistic slope fragility assessment accounting for uncertainty associated with the temporal patterns of rainfall intensity. Hourly-scale random time series for the rainfall event are generated, considering uncertainties in temporal patterns of rainfall intensity, using the statistical concepts of skewness and kurtosis within the Pearson system of distributions. A time-dependent seepage-stability mechanical model coupling the finite element method and limit equilibrium method for the slope under hourly-scale rainfall time series is established. Slope fragility assessment under rainfall is conducted, accounting for uncertainties in temporal patterns of rainfall intensity based on Monte Carlo simulation. An illustrative example is provided, focusing on a hypothetical soil slope in the southeastern coastal area of China, susceptible to rainfall-induced landslides. The impact of skewness and kurtosis of rainfall time series on the slope failure probability and failure time are examined. [ABSTRACT FROM AUTHOR]

Recent probabilistic studies have thoroughly examined how uncertainties in soil shear strength affect slope stability, while the impact of spatial variability in soil porosity on post-failure behaviors of slopes has received less attention. Overlooking the influence of porosity may lead to inaccurate assessments of slope post-failure behaviors. This study presents a random smoothed particle hydrodynamics (RSPH) framework for probabilistic analysis of slope failure with large deformation using a critical state-based hypoplastic constitutive model. The results indicate that the proposed RSPH method provides reasonable estimates for slope post-failure behaviors. Increases in both the coefficient of variation (COV) and the scale of fluctuation (SOF) of porosity give rise to underestimations of the run-out distance and sliding volume. Additionally, slope failure modes are affected by increasing uncertainty of porosity, which may contribute to the occurrence of deep-seated failures. [ABSTRACT FROM AUTHOR]

To efficiently and accurately assess the stability of the rock slope, a reliability analysis approach based on the Partitioned Rigid Element and Interface Element (PRE-IE) method and the Advanced First-Order Second-Moment (AFOSM) method is proposed. Utilizing the PRE-IE method for effective calculation of tangential and normal forces on potential sliding surfaces, constructing an explicit performance function based on the Mohr–Coulomb criterion. The reliability of the rock slope was calculated using the AFOSM method, with the rock mass unit weight, cohesion, and friction coefficient on structural planes considered as random variables. A typical case study is presented, using results from Monte Carlo Simulation (MCS) as a benchmark to compare the proposed approach with mean-value First-Order Second-Moment(FOSM) and Response Surface Method (RSM), validating its accuracy and efficiency. Conducting a reliability analysis of a rock slope near the reservoir of a large hydropower station provides a practical case study in engineering. The calculation results indicate that the loose structure zone in the shallow surface layer of the slope has a risk of instability, which is consistent with actual observational data, proving the applicability of this approach for evaluating the reliability of rock slopes stability. [ABSTRACT FROM AUTHOR]

Infinite slope analysis has been advocated and employed by many researchers because of its simplicity and conservative outcomes. Although the analysis has undergone extensive revisions with the assumption of linear failure criteria for soil slopes, it has rarely been used in rock engineering. This study proposes a theoretical framework for infinite rock slope analyses, particularly for rock masses weakened by weathering and other geological processes. The consequence of eliminating the tensile strength by assuming a highly fractured rock mass is examined using the exact solution obtained from both static and kinematic approaches. The analysis results indicate that the influence of tension cut-off becomes apparent due to reduction in the effective normal stress as a consequence of a steep slope and seepage flow. A unique characteristic of an infinite rock slope, where the length of the hypotenuse from the origin to the limit stress on the strength envelope is equal to the stability factor, is further discussed for various extents, such as seepage flow, factor of safety, and modified failure criterion with tension cut-off. Such graphical considerations clearly reveal the influence of various parameters involved in the analysis and provide useful insights into infinite rock slopes. [ABSTRACT FROM AUTHOR]

In geotechnical earthquake engineering, the seismic displacement is regarded as a more balanced index to explain the co-seismic performance of soil slopes. The Newmark's sliding block theory is usually adopted to fast estimate the seismic slope displacement, and subject to different assumptions of the sliding soil mass, various improvements can be made onto the Newmark's sliding block models. In this paper, the Newmark's sliding block model is further modified to calculate the seismic displacement of shallow slopes composed of cohesive soils. The research significance is highlighted by several novel considerations: (1) the yield acceleration of translational sliding soil column derived from infinite slope model is modified to be displacement-dependent and is analytically expressed by simulating the seismic strain-softening effect of the undrained soil shear strength; (2) subjected to rotational sliding mode, the slope yield acceleration is further modified to reflect the change of slip surface geometries in the course of co-seismic downward slope movement; and (3) the seismic slope displacement model fully considers the flexibility of the soil mass by simulating the nonlinear dynamic vibration response of flexible soil columns, which is further coupled within the Newmark's sliding block model. Verifications of the proposed modelling procedure were made by seismic displacement analysis of several numerical examples against strong earthquake records provided by NGA-West2. The comparison results calculated from different models show that ignoring the dynamic characteristics of the slope yield acceleration will underestimate the seismic slope displacement to some extent, which is undesirable in geotechnical risk management. [ABSTRACT FROM AUTHOR]

This paper investigates the hydromechanical behaviors of geogrids-reinforced expansive soil slopes under repeated external climate actions through a series of case study, laboratory tests, and numerical simulation. In the case study, the moisture content and horizontal earth pressure (σ h) of a geogrids-reinforced expansive soil and the tensile strain of the geogrids were monitored for two years. Numerical simulations, based on indoor test results of the in-situ soil, were conducted to further investigate the behaviors of the slope upon infiltration. It is found that the surficial reinforced layer is effective in isolating the underlying natural expansive soils from the external drying-wetting processes. The geogrids reduce the swelling of the expansive soil upon rainfall without inducing excessive increment in the σ h or geogrid strain. Consequently, the geogrid reinforcement effectively improves the stability of the slope under the actions of weathering and swelling. The highest horizontal displacement and earth pressure, and the yielding and shear failure of the reinforced expansive soil take place at the foot of the slope. A new approach for assessing the global stability of the geogrids-reinforced expansive soil layer, which receives less attention in existing design approaches, is proposed and validated by the results of the current study. [ABSTRACT FROM AUTHOR]

The discrete element method (DEM) has been widely used to simulate geotechnical works, e.g. slopes, embankments, tunnels, pipelines, etc. since the last decade. However, how to choose the appropriate input parameters still remains problematic and greatly affects the accuracy of DEM modelling results. One of the common practice is to calibrate DEM parameters using lab or in-situ tests. Such operation is largely dependent on personal judgement and thus induces errors to the numerical modeling results. Therefore, a novel framework based on particle swarm optimization (PSO) algorithm was proposed in this study, which could calibrate parameters using 3 or more macro-indicators. The framework was written in Python, which performed automatic calibration process and thus minimized involvement of personal judgement. To validate its effectiveness, the framework was applied to the simulation of biaxial tests on sand first. The calibration results showed that similar parameters were yielded when different initial values were fed to the framework. Then, the framework was applied to simulation of soil-rock mixture (S-RM), and the calibration process was effective as well. These two cases proved that the proposed framework was an efficient tool for DEM parameter calibration and largely reduced computation errors resulting from personal judgement. [ABSTRACT FROM AUTHOR]

Traditional deterministic slope stability analysis frequently neglects the influence of various uncertainties inherent in soil properties. Recently, probabilistic analysis has seen great success in slope stability analysis, however, the direct simulation of low-level failure probabilities of earth slopes still faces some computational challenges. To solve such an issue, this study presents an improved weighted low-discrepancy simulation (WLDS) method for efficient probabilistic slope stability analysis, especially for random variable model (RVM). This method incorporates a series of intermediate events into the WLDS framework, effectively transforming the calculation of failure probability into a product of relatively large conditional probabilities, which can significantly improve the computational efficiency. In accordance with probabilistic theory, the variance in the probability of generating randomized low-discrepancy samples within a specified subset is employed as a viable criterion to determine intermediate threshold values. Furthermore, to increase the likelihood of the sample generation in each intermediate event, a reduction strategy for intermediate sampling space is adopted, which can enhance the sampling efficiency to generate conditional samples. The efficiency and accuracy of the proposed method are demonstrated through one mathematical function case and three slope stability cases. In combination with probabilistic weight strategy, the multiple most probable failure points (multi-MPPs) can be easily identified, which represents different slope failure modes. Last but not least, when dealing with correlated random variables, the unique capability of the proposed method in reliability updating with no additional evaluations of performance function is discussed. [ABSTRACT FROM AUTHOR]

The anchor cable is a widely used reinforcement device in geotechnical engineering. However, conservative assessment results are provided by existing methods due to neglecting the strength reserve of anchor cables. To address this issue, this work establishes a model considering the safety reserve of anchor cables by incorporating the influence of the axial force increment of anchor cables on slope stability within the framework of the minimum potential energy method. The potential sliding mass is regarded as an ellipsoid controlled by six parameters, and the failure surface corresponding to the maximum sliding direction of slopes is considered as the critical slip surface. The reasonableness of the proposed method is tested with three benchmark cases and an engineering example. These outcomes indicate that safety factor obtained by considering the axial force increment of anchor cables is higher than that predicted by the traditional theory, and the growth rate of SF decreases with an increase in the foundation coefficient. The optimal anchor angle is strongly influenced by the vertical spacing of anchor cables as well as the installation height of the first row of anchor cables, while the shear parameters of soil have almost no effect on it. • A new perspective for assessing the stability of 3D reinforced slopes is introduced. • A model that considers the strength reserve of anchor cables is developed. • Effects of foundation coefficient on the axial force of anchor cables are explored. • Range of optimal anchor angle is suggested. [ABSTRACT FROM AUTHOR]

The Bisection Method is a common search strategy implemented as part of the shear strength reduction procedure for finite element slope stability analysis. Despite the Bisection Method's simplicity and reliability as a root finding technique, it is generally accepted to achieve slower rates of convergence than many alternatives. The aim of this paper is the description of an efficient method for performing shear strength reduction using root bracketing techniques, specifically for Finite Element slope stability analysis. The False Position (regula falsi) Method enables computationally intensive slope models to be simulated by minimising the total number of solver iterations required to determine the factor of safety. Several finite element models are presented to highlight the applicability of the given methods, with significant savings made (in the order of 50 percent) with respect to two of the most common strength reduction procedures − uniform incrementation and the Bisection Method. In all cases, strong agreement in safety factors is observed between traditional strength reduction methods and the proposed techniques. [ABSTRACT FROM AUTHOR]

The paper deals with the mechanical behaviour of a natural volcanic silty soil sampled from steep slopes. This soil is very loose and unsaturated over most of the year due to climate conditions. Thus so-called wetting collapse and static liquefaction may occur during rainfall. Major issues are posed once the slides turn into flows with high destructive potential. However, the modelling of the constitutive behaviour is challenging and not yet available in the literature for this soil. A recent Generalized Plasticity Model was selected as it is capable to adequately take into account the effects of change in soil porosity, bonding related to the matric suction normalized versus soil porosity, and static liquefaction proneness. The model is calibrated for 37 saturated/unsaturated laboratory tests, and the performance of the model is assessed quantitatively. It is newly shown that the model – with one single set of constitutive parameters – is capable to well describe the soil mechanical response, in unsaturated and saturated conditions, experienced by the soil in different laboratory devices and along different stress paths. Those insights provide a theoretical framework for designing further laboratory tests, improving the understanding of this complex natural soil, and implementing better modelling of landslides of the flow-type. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study investigating the hydraulic response and stability of geosynthetic-reinforced soil slopes subject to rainfall. A series of numerical simulations of unsaturated slopes with various backfill–reinforcement–drainage systems subject to rainfall infiltration was performed by comprehensively considering the combined effect of backfill (i.e., sand, silt, and silty clay), reinforcement type (i.e., geogrid or nonwoven geotextile), and rainfall intensity (350 and 500 mm/day). The backfills were modeled using three soil–water characteristic curves (SWCCs) representing the general suction range associated with sand, silt, and clay. The influence of sand cushions in improving the stability of reinforced clay slopes was also assessed. The numerical results reveal that the loss of matric suction and development of a capillary barrier effect within clay backfills could have adverse impacts on both the global and local stabilities of the reinforced clay slopes. The contribution of matric suction in enhancing slope stability was initially high for reinforced clay slopes; however, the global stability of the reinforced clay slope substantially decreased due to the loss of matric suction as the rainfall infiltration proceeded. The local instability of the geotextile-reinforced clay slope occurred due to the capillary barrier effect at the geotextile–clay interface. The reinforced marginal soil slopes cannot effectively drain the infiltrating water under torrential rainfall. Free drainage conditions may not be assumed for these slopes if the drainage is not properly considered. Both the global and local factors of safety (FS) of the reinforced sand slope were minimally influenced by the loss of matric suction induced by rainfall infiltration. The required reinforcement tensile strengths for the reinforced silt and clay slopes to maintain FS  = 1.3 were, respectively, approximately 3 and 4 times larger than that for reinforced sand slopes. Numerical results also indicated that the inclusion of sand cushions, which provide both strength and drainage functions, can effectively enhance the slope stability. An optimal sand cushion thickness of 15 cm (replacing 20% of marginal backfill with sand) was determined in this study. [ABSTRACT FROM AUTHOR]

In contrast to conventional kinematic analysis postulating a log-spiral failure mechanism, this study adopts a discretization technique to generate a kinematically admissible failure mechanism, using the forward difference method. A vertical infinitesimal trapezoidal element, similar to that in slices method of limit equilibrium, is chosen so as to consider pore water effect within slopes. The work rate-based balance equation yields the optimal kinematic solution of limiting surcharge near the crest of the slope. The bearing capacity of a saturated non-uniform slope is sought through optimization and verified with conventional kinematic analysis. [ABSTRACT FROM AUTHOR]

A data assimilation framework, utilising measurements of pore water pressure to sequentially improve the estimation of soil hydraulic parameters and, in turn, the prediction of slope stability, is proposed. Its effectiveness is demonstrated for an idealised numerical example involving the spatial variability of saturated hydraulic conductivity, k sat . It is shown that the estimation of k sat generally improves with more measurement points. The degree of spatial correlation of k sat influences the improvement in the predicted performance, as does the selection of initial input statistics. However, the results are robust with respect to moderate uncertainty in the spatial and point statistics. [ABSTRACT FROM AUTHOR]

A glass fiber reinforced polymer (GFRP) material is a newly developed material for slope reinforcement. In this study, distributed optical fiber sensors are developed to characterize the interface shear stress–strain behavior in GFRP soil nails with a strain-transfer model. The GFRP bar with a diameter of 40 mm was used as a reinforcing element in a soil slope subjected to excavations. A newly distributed fiber optic sensors are developed to measure the axial strains of the GFRP reinforcement which was then inserted into a drilled hole together with pressure grouting. The calibration of distributed fiber optic sensors indicated that the strains along the GFRP bar can be accurately measured by the distributed sensors. An analytical strain-transfer model is developed and then verified with a finite element model. The comparisons indicate that the strain-transfer model could be able to obtain the shear strain and stress at the cement grout–soil interface from arbitrary strain of the GFRP bar. Finally, a field project study is conducted for the condition assessment of a GFRP soil nail with the interface shear stress at different excavation depths. The potential failure surface is identified at the position where the maximum shear stress occurs, that is, at the point around 4.5 m away from the soil nail head. Results in terms of the shear stress are able to detect the active and passive zones of the soil nail. A further analysis indicates that the health condition of the GFRP soil nail can be determined with the distributed fiber sensors and strain-transfer model. [ABSTRACT FROM AUTHOR]

Geological uncertainty is often ignored in slope reliability analysis, even though the inherent variability of soil parameters is considered. This paper aims to propose a method for slope reliability analysis by considering both the inherent variability of soil parameters and geological uncertainty. A coupled Markov chain (CMC) model is used to simulate the geological uncertainty. An implementation procedure for slope reliability considering the aforementioned two types of uncertainty is provided. A slope reliability problem is analyzed to validate the proposed method with the borehole data from Perth, Australia. Different borehole layout schemes are designed to reflect the effect of both number and location of boreholes on slope reliability. Moreover, which type of uncertainty mentioned above has a greater impact on slope reliability is explored. The results indicate that the proposed method can effectively evaluate the slope reliability considering these two types of uncertainty. If only the inherent variability is considered, the accuracy of reliability analysis mainly depends on the used geological profiles. Borehole layout scheme has a significant effect on slope reliability. Both probability of failure ( P f ) and mean of factor of safety ( FS ) of slope do not monotonously vary with an increasing number of boreholes. The boreholes designed in the critical influence zone can provide more information to improve the accuracy of slope reliability. The coefficients of variation (COVs) of shear strength parameters and the discrepancy among the means of shear strengths for different soils play different and major role between the two types of uncertainty in the reliability analysis of soil slope. [ABSTRACT FROM AUTHOR]

This paper investigates the settlement behaviour of a strip footing seating on the crest of an embankment and subjected to cyclic loading. The embankment fill is a dense sand and the issue is the gradual accumulation of settlement over a large number of load repetitions. Cyclic triaxial tests were first conducted to develop a consistent but simple material model for numerical implementation. Particular emphasis was placed on linking the stress-strain behaviour of an unload-reload cycle to the accumulation of permanent strain, with only five input parameters required to model the cyclic behaviour. The material model was implemented in a numerical analysis to compute the settlement behaviour obtained from model tests conducted by another researcher. It is pertinent to highlight that the same soil, compacted to same density at same moisture content, was used for both the cyclic triaxial tests and model tests. Reasonable to good agreement between the experimental and numerical results was achieved. [ABSTRACT FROM AUTHOR]

A rigid block based lower bound limit analysis method for analyzing stability of fractured rock mass in 2D and 3D conditions is proposed. The rock bridge effects are considered in the general formation. No assumptions are imposed on the inter-element forces, and the solution obtained is statically admissible. The proposed method is theoretically rigorous and simple. The validation and efficiency of the proposed method have been demonstrated through three typical types of slopes, indicating that apart from the fractures, rock bridge plays a key role in stabilizing rock blocks, which should be greatly concerned in stability analysis of rock mass. [ABSTRACT FROM AUTHOR]

Discarding known data from cored samples in the reliability analysis of a slope in spatially variable soils is a waste of site investigation effort. The traditional unconditional random field simulation, which neglects these known data, may overestimate the simulation variance of the underlying random fields of the soil properties. This paper attempts to evaluate the reliability of a slope in spatially variable soils while considering the known data at particular locations. Conditional random fields are simulated based on the Kriging method and the Cholesky decomposition technique to match the known data at measured locations. Subset simulation (SS) is then performed to calculate the probability of slope failure. A hypothetical homogeneous cohesion-frictional slope is taken as an example to investigate its reliability conditioned on several virtual samples. Various parametric studies are performed to explore the effect of different layouts of the virtual samples on the factor of safety (FS), the spatial variation of the critical slip surface and the probability of slope failure. The results suggest that whether the conditional random fields can be accurately simulated depends highly on the ratio of the sample distance and the autocorrelation distance. Better simulation results are obtained with smaller ratios. Additionally, compared with unconditional random field simulations, conditional random field simulations can significantly reduce the simulation variance, which leads to a narrower variation range of the FS and its location and a much lower probability of failure. The results also highlight the great significance of the conditional random field simulation at relatively large autocorrelation distances. [ABSTRACT FROM AUTHOR]

This paper develops an analytical approach for reliability analysis of infinite slope stability in presence of spatially variable shear strength parameters. The analytical approach considers spatial autocorrelation of each parameter and cross-correlations between different parameters. It is robust, computational efficient and provides insight to the importance of spatial correlation scale on slope reliability analysis. This paper also explores the difference in continuous and discrete random fields and emphasizes the importance of fine discretization in relation to correlation scale. Finally, it shows that conditioning the stability analysis with information about trends and spatial data leads to reliability assessments with less uncertainty. [ABSTRACT FROM AUTHOR]

In this paper, a polar slice method is proposed to quantify the energy dissipation in the inner sliding soil mass and evaluate the slope stability in rotational failure mechanism. The polar slice method is compared with the vertical slice method. Despite similar results, the advantages of the polar slice method are explained. Besides, the comparison between the polar slice method and Chen’s method shows that the polar slice method would lead to more accurate results than Chen’s method, while Chen’s method which neglects the energy dissipation in the inner sliding soil mass is relatively conservative. [ABSTRACT FROM AUTHOR]

By combining the numerical stability of the global analysis method and the flexibility of the Morgenstern-Price method, a global procedure for the stability analysis of slopes is developed. Firstly, based on the Morgenstern-Price assumption of inter-slice forces, an expression for the distribution of normal stress on the sliding surface is derived. Then, the equilibrium equations of the sliding body are built. Finally, three different expressions for the distribution of normal stress on the sliding surface are proposed, followed by the comparison of their effects and the stability analysis of a large-scale landslide exposed during the construction of a hydropower project. [ABSTRACT FROM AUTHOR]

One of the most applicable geotechnical structures whose analysis is carried out through iterative procedures is the reinforced soil slope. In this regard, the most successful method for the reinforced slope analysis through numerical methods is the finite element method whose updating mesh may result in some difficulties. In this study, the Natural Element Method (NEM), which is a mesh-free method, in conjunction with conventional limit equilibrium is implemented to find the slip surface in the reinforced slopes. Results demonstrate the convergence and preciseness of the present method in comparison with the other numerical methods and conventional limit equilibrium method. [ABSTRACT FROM AUTHOR]

System effects should be considered in the probabilistic analysis of a layered soil slope due to the potential existence of multiple failure modes. This paper presents a system reliability analysis approach for layered soil slopes based on multivariate adaptive regression splines (MARS) and Monte Carlo simulation (MCS). The proposed approach is achieved in a two-phase process. First, MARS is constructed based on a group of training samples that are generated by Latin hypercube sampling (LHS). MARS is validated by a specific number of testing samples which are randomly generated per the underlying distributions. Second, the established MARS is integrated with MCS to estimate the system failure probability of slopes. Two types of multi-layered soil slopes (cohesive slope and c – φ slope) are examined to assess the capability and validity of the proposed approach. Each type of slope includes two examples with different statistics and system failure probability levels. The proposed approach can provide an accurate estimation of the system failure probability of a soil slope. In addition, the proposed approach is more accurate than the quadratic response surface method (QRSM) and the second-order stochastic response surface method (SRSM) for slopes with highly nonlinear limit state functions (LSFs). The results show that the proposed MARS-based MCS is a favorable and useful tool for the system reliability analysis of soil slopes. [ABSTRACT FROM AUTHOR]

Little insight exists into the stability of reinforced slopes supporting spread footings. Existing research is largely focused on idealized, plane strain analyses that do not account for three-dimensional conditions. These conditions are significant because the geometries of both reinforced slopes and footings are three-dimensional in nature. In this study, the stability of reinforced slopes supporting spread footings is analyzed in three dimensions using a limit analysis approach and presented in a series of design charts. To better understand the impact of three-dimensional conditions, a parametric study is conducted to evaluate effects of various design parameters on required reinforcement strength. [ABSTRACT FROM AUTHOR]

Retrogressive and progressive slope failures are a dynamic process, in the sense that they involve a progressively changing scenario. This paper uses the contemporary material point method (MPM), to provide a view of how such failures develop. Two main scenarios are presented: (a) a relatively small slope, which, when subjected to an initial failure, is steepened, leading to the initiation of further failures retrogressing backwards; and (b) a long slope, where an initial perturbation (e.g. an excavation) triggers a series of failures that can retrogressively move up-slope. [ABSTRACT FROM AUTHOR]

Slope stability analysis generally considers a homogeneous slope composed of either soil or rock. There is no definitive criterion to distinguish homogeneous and heterogeneous slopes. This paper presents five model tests on two-layered slopes with different interface subjected to surcharge load. Numerical simulations were performed to capture the behaviors observed. Given the satisfactory reproduction of the model tests, a parametric study was then conducted to investigate the impact of the interface, slope angle and strength parameters. Finally, a set of criteria based on the relative cohesion ratio was proposed to characterize a distinct change in the nature of the slope. [ABSTRACT FROM AUTHOR]

A method to analyse potential excavation geometries, termed excavation isoplethogram, has previously been proposed for use in civil or mining engineering. The results are typically presented in the form of a contour plot identifying orientations of proposed excavation planes that may lead to large volumes (or masses) of unstable blocks and wedges. In this paper, a novel algorithm is proposed to utilise the probabilistic discrete fracture network approach to quantify the risk associated with various slope designs. The method is applied using open cut mine data in order to demonstrate its potential for decision making in mine design and operations. [ABSTRACT FROM AUTHOR]

Geological uncertainty appears in the form of one soil layer embedded in another or the inclusion of pockets of different soil type within a more uniform soil mass. Uncertainty in factor of safety (FS) and probability of failure (Pf) of slope induced by the geological uncertainty is not well studied in the past. This paper presents one approach to evaluate the uncertainty in FS and Pf of slope in the presence of geological uncertainty using borehole data. The geological uncertainty is simulated by an efficient coupled Markov chain (CMC) model. Slope stability analysis is then conducted based on the simulated heterogeneous soils. Effect of borehole layout schemes on uncertainty evaluation of FS and Pf is investigated. The results show that borehole within influence zone of the slope is essential for a precise evaluation of FS statistics and Pf. The mean of FS will converge to the correct answer as the borehole number increases. [ABSTRACT FROM AUTHOR]

In the past, the response of stabilizing piles subjected to lateral soil movement or lateral force loading has been analysed assuming that the piles are embedded in horizontal semi-infinite soil grounds. In this study, a limit equilibrium method analysing the lateral force (soil–pile pressure per unit thickness) on stabilizing piles embedded in semi-infinite slopes is presented. In addition, the soil arching effects between two neighbouring stabilizing piles are analysed, and the lateral active stress in the rear of the piles is obtained. Furthermore, the squeezing effect between two piles proposed by Ito and Matsui is combined with the lateral active stress in the slope to evaluate the distribution of the soil–pile pressure per unit length of the stabilizing piles in sandy slopes. A numerical simulation using FLAC 3D is used to evaluate the proposed approach. The simulation shows that the proposed model could reasonably predict the shape of the distribution of the soil–pile pressure acting on the stabilizing piles, while some discrepancy exists between the numerical results and predicted values. Furthermore, the prediction of the proposed model is also evaluated through comparison to the experimental data from the published literature. Parametric analysis is carried out to investigate the influence of the slope angle on the distribution of the soil–pile pressure. The shape of the distribution of the soil–pile pressure acting on the piles is shown to vary with the angle of the slope, while the magnitude of the soil–pile pressure remains in the same order. [ABSTRACT FROM AUTHOR]

This study examines the applicability of point estimate methods (PEMs) in the probabilistic stability analysis of slopes. For illustrative purposes, two slopes indicating two different mechanisms of failure are selected and probabilistic analyses are performed employing three PEMs that have been widely cited in different literature reports. To evaluate the benefits and shortcomings of each PEM, various cases are studied in which random parameters may be dependent or independent and can have arbitrary distributions. Furthermore, the efficiency and accuracy of the considered PEMs are assessed by comparing the results with those obtained by Monte Carlo Simulation (MCS). The results indicate that the considered PEMs are sufficiently precise and, in case an intricate geotechnical structure must be probabilistically analysed, they can readily be incorporated with numerical methods. [ABSTRACT FROM AUTHOR]

This paper presents stability charts of homogeneous isotropic slopes developed by the upper bound limit analysis theory and strength reduction technique. The objective function of the homogeneous isotropic slope safety factor is optimized by nonlinear sequential quadratic programming. The stability charts of homogeneous isotropic slopes under simple conditions are developed by the analysis of substantial data and those of slopes under different conditions, by considering the effects of typical factors such as surcharge load, pore water pressure, and horizontal seismic forces. These charts can be quickly and easily used to determine the safety factor and corresponding slope failure mechanism under different typical conditions. The failure mechanisms of sample slopes under different conditions are provided to illustrate the uses of these stability charts. [ABSTRACT FROM AUTHOR]

Abstract: Rainfall-induced landslides in steep soil slopes of volcanic origin are a major threat to human lives and infrastructure. In the context of constructing early warning systems in regions where extensive data on landslide occurrences and associated rainfall are inexistent, physically-based tools offer the possibility to establish thresholds for measurable field quantities. In this paper, a combined finite element infinite slope model is presented to study the transient hydraulic response of volcanic ash slopes to a series of rainfall events and to estimate seasonal safety factors. Furthermore, analytical considerations of partially saturated infinite slopes are made to define capillary stress thresholds for a landslide early warning system. [Copyright &y& Elsevier]

Abstract: The permeability function for a soil may change spatially due to uncertainties in soil fabric. The main objective of this paper is to investigate how the spatial variability of permeability function propagates to the variability of the pore-water pressures and groundwater table in a slope as well as the stability of the slope. A random field analysis method is explored by assigning discrete random values to a 2D space and controlling the density of random field grid to improve the calculation accuracy. Sequences of random numbers are generated using fast Fourier transform. In a given heterogeneous slope subject to steady-state rainfall infiltration, a parametric study shows that the matric suctions are 0.5–1.25 times those in a homogeneous slope when the correlation length of log-permeability varies from 0.4 to 50 times the slope height. The groundwater table is no longer unique with a spatially variable permeability function. There exists a critical correlation length approximately five times the slope height at which the change in the groundwater table is maximal and the mean factor of safety is minimal. The mean factor of safety of the heterogeneous slopes is smaller than that of a homogenous slope with mean input parameters. The spatial variability of soil influences the range of the calculated factor of safety significantly but does not influence the mean factor of safety substantially. [Copyright &y& Elsevier]

Abstract: While the evolution with time of the factor of safety against slope failure is well understood for excavations performed under fully saturated conditions, this evolution has not been extensively studied for excavations carried out in unsaturated soils. The objective of this paper is to investigate the relationship between the factor of safety and time for an excavation performed in an unsaturated silty soil, employing the finite element method. A hypothetical boundary value problem is considered and two types of analyses performed; in the first one, unsaturated soil behaviour is modelled through appropriate constitutive and soil–water retention curve models, whereas in the second one full saturation is assumed. The effect that the saturated soil permeability, its variation with suction, the increase of apparent cohesion due to suction, the depth of the groundwater table and the hydraulic hysteresis have on the results of the unsaturated analysis is examined in a parametric study. The analyses results demonstrate that for unsaturated soils the factor of safety may increase with time, in contrast to what is commonly accepted to be the case in fully saturated soils. Furthermore, it is not possible to know in advance which one of the two types of analysis performed (i.e. the saturated or the unsaturated) will produce conservative results. It is, therefore, advisable to perform unsaturated analysis in geotechnical practice, when dealing with excavations in such soils. [Copyright &y& Elsevier]

Abstract: A key issue in assessment of rainfall-induced slope failure is a reliable evaluation of pore water pressure distribution and its variations during rainstorm, which in turn requires accurate estimation of soil hydraulic parameters. In this study, the uncertainties of soil hydraulic parameters and their effects on slope stability prediction are evaluated, within the Bayesian framework, using the field measured temporal pore-water pressure data. The probabilistic back analysis and parameter uncertainty estimation is conducted using the Markov Chain Monte Carlo simulation. A case study of a natural terrain site is presented to illustrate the proposed method. The 95% total uncertainty bounds for the calibration period are relatively narrow, indicating an overall good performance of the infiltration model for the calibration period. The posterior uncertainty bounds of slope safety factors are much narrower than the prior ones, implying that the reduction of uncertainty in soil hydraulic parameters significantly reduces the uncertainty of slope stability. [Copyright &y& Elsevier]

Abstract: Soil–water characteristic curve (SWCC) is the most fundamental and important soil property in unsaturated soil mechanics. It has been used for analyzing slope stability due to the infiltration of rainfall into slopes and water flow in unsaturated embankments. Generally, SWCC is obtained by laboratory tests. However high cost, long duration and difficulty of the tests impede the application of unsaturated soil mechanics to practical design or analysis. Therefore, several equations have been developed to predict the SWCC using grain-size distribution (GSD) curve. However, most of the equations were limited to soils with unimodal characteristics and the parameters of the equations are not related to the physical properties of the soil. In this paper, an equation to predict SWCC for soils with bimodal characteristics is proposed. The parameters of the proposed equation are related to the physical properties of soil and the variables of SWCC closely. The proposed equation is evaluated with data from the literature and laboratory tests carried out in this study. In addition, the computer codes for the computation of the predicted bimodal SWCC are presented. [Copyright &y& Elsevier]

Abstract: A novel particle based Bluff Morphology Model (BMM) developed by the authors is extended in this paper to investigate the effect of two dimensional seepage on the stability and collapse of soil slopes and levees. To incorporate the seepage in the model, Darcy’s law is applied to the interactions among neighbouring soil particles and ghost particles are introduced along the enclosed soil boundary so that no fluid crosses the boundary. The contribution of partially saturated soils and matric suction, as well as the change in hydraulic conductivity due to seepage, are predicted well by the present model. The predicted time evolution of slope stability and seepage induced collapse are in reasonable agreement with the experimental results for homogeneous non-cohesive sand and multiple layered cohesive soils. Rapid drawdown over a sand soil is also investigated, and the location and time of the levee collapse occurrence are well captured. A toe erosion model is incorporated in the BMM model, and the location and quantity of erosion from lateral seepage flow is well predicted. The interplay of erosion, seepage and slope instability is examined. [Copyright &y& Elsevier]

Abstract: Lower bound dynamic shakedown theory is a limit state method. It is employed herein to investigate the safety, which is associated with permanent displacement, of slopes under repeated dynamic loads, mainly earthquakes. An efficient numerical method, previously applied to the static shakedown of pavements, is extended to the dynamic shakedown of slopes in this study. It is shown that dynamic shakedown, unlike other limit state methods, is able to consider the dynamic properties of both the load and subsoil. The effect of the soil strength parameters and dynamic features of the soil and loads are examined thoroughly and some illustrative examples are employed. The short-term and long-term behavior of slopes under seismic loads are studied as well, comparing results of the present study with the well-known displacement method of Newmark. [Copyright &y& Elsevier]

Abstract: The paper presents a new procedure for the analysis of slope stabilization using piles. The developed method allows the assessment of soil pressure and its distribution along the pile segment above the slip surface based on soil–pile interaction. The proposed method accounts for the influence of pile spacing on the interaction between the pile and surrounding soils and pile capacity. The paper also studies the effect of soil type, and pile diameter, position and spacing on the safety factor of the stabilized slope. Specific criteria are adopted to evaluate the pile capacity, ultimate soil–pile pressure, development of soil flow-around failure and group action among adjacent piles in a pile row above and below the slip surface. The ability of the proposed method to predict the behavior of piles subject to lateral soil movements due to slope instability is verified through a number of full scale load tests. [Copyright &y& Elsevier]

Abstract: Although first-order reliability method is a common procedure for estimating failure probability, the formulas derived for bimodal bounds of system failure probability have not been widely used as expected in present reliability analyses. The reluctance for applying these formulas in practice may be partly due to the impression that the procedures to implement the system reliability theory are tedious. Among the methods for system reliability analysis, the approach suggested in Ditlevsen 1979 is considered here because it is a natural extension of the first-order reliability method commonly used for failure probability estimation corresponding to a single failure mode, and it can often provide reasonably narrow failure probability bounds. To facilitate wider practical application, this paper provides a short program code in the ubiquitous Excel spreadsheet platform for efficiently calculating the bounds for system failure probability. The procedure is illustrated for a semi-gravity retaining wall with two failure modes, a soil slope with two and eight failure modes, and a loaded beam with three failure modes. In addition, simple equations are provided to relate the correlated but unrotated equivalent standard normals of the Low and Tang 2007 FORM procedure with the uncorrelated but rotated equivalent standard normals of the classical FORM procedure. Also demonstrated are the need for investigating different permutations of failure modes in order to get the narrowest bounds for system failure probability, and the use of SORM reliability index for system reliability bounds in a case where the curvature of the limit state surface cannot be neglected. [Copyright &y& Elsevier]

Abstract: Soil nailing is the most popular technique for stabilizing newly formed and existing sub-standard slopes in Hong Kong because of its economic and technical advantages. The nail–soil interface shear resistance is an important parameter in design of soil nailed structures. A three-dimensional finite element model was established and used for simulating soil nail pull-out tests. The finite element model was verified by comparing simulated results with measured data. The agreement between the experimental and simulated results in terms of both average pull-out shear stress and stress variation was very good. Using this finite element model, a parametric study was carried out to study the influences of the overburden pressure and soil dilation angle on the soil nail pull-out resistance. The simulated peak pull-out resistance was not directly related to the overburden pressure, which was coincident with the observations in laboratory pull-out tests. The simulated pull-out resistance increased significantly with the increase in dilation angle of the shearing zone. This analysis indicated that the constrained dilatancy of the nail–soil interface and the soil surrounding the nail contributed a lot to the development of peak pull-out resistance. [Copyright &y& Elsevier]

Abstract: The effect of inclined loading on the bearing capacity of foundations on horizontal ground surface is well established and both the exact solution and simpler empirical equations are available for the calculation of the failure loads. However, for footings on or near slopes complete solutions are available only for vertical loading. This paper investigates the influence of inclined loading on the horizontal and vertical failure loads. The finite element, upper bound plasticity and stress field methods are used to examine a wide range of geometries and soil properties. The methods are first validated against known solutions for two special cases and are subsequently employed to investigate the effect of the geometrical and material properties on the failure loads and the bearing capacity load interaction diagram. Based on this investigation an empirical equation is proposed for the load interaction diagram for undrained inclined loading of footings on or near slopes. [Copyright &y& Elsevier]

Abstract: This paper uses numerical finite element upper and lower bound limit analysis to produce stability charts for three dimensional (3D) homogeneous and inhomogeneous undrained slopes. Although the conventional limit equilibrium method (LEM) is used more often in practice for evaluating slope stability, the accuracy of the method is often questioned due to the underlying assumptions that it makes. Using the limit theorems can not only provide a simple and useful way of analysing the stability of slopes, but also avoid the shortcomings and arbitrary assumptions under pinning the LEM. The rigorous limit analysis results in this paper were found to bracket the slope stability number to within ±9% or better and therefore can be used to benchmark for solutions from other methods. In addition, it was found that using a two dimensional (2D) analysis to analyse a 3D problem will lead to a significant difference in the factors of safety depending on the slope geometries. This is of particular relevance to any back analyses of slope failure as it will lead to an unsafe estimation of material strengths. [Copyright &y& Elsevier]

Abstract: Soil nailing has been widely used as a reinforcing technique to retain excavations and stabilise slopes. Proper assessment of the interaction between the nails and the surrounding soil is central to safe and economical design of the composite reinforced soil structure. In this note, a new interface model, denoted as “embedded bond-slip model”, is proposed to model the soil–nail interaction numerically in a simplified manner. Combining the key features of the embedded element technique and the conventional interface element method, the proposed plane–strain interface model has the advantages that no special considerations have to be given to the arrangement of the finite element mesh for the soil nails, and that possible tangential slippage along the interface can be modelled. The formulation also allows pore water flow across the soil nails to be incorporated into the analysis. The proposed model has been implemented into a finite element code and verified by simple element tests under different uni-direction loading conditions. Using the proposed interface model, back analyses of a field test involving a soil-nailed cut slope subjected to a rise in groundwater table have been conducted. This note presents the details of the embedded bond-slip model and the numerical results which demonstrate that the proposed model is capable of simulating soil–nail interaction conveniently and realistically. [Copyright &y& Elsevier]

Abstract: Assessment of the stability of embankment and cut slopes over the life of a project are critical issues for railway and motorway infrastructure projects. Experience has shown that many slope failures occur during or shortly after rainfall. Analyses show that failure is initiated by the reduction in near surface suction over some critical depth in the slope. A simple method is proposed in this paper to estimate the time needed for a wetting front to develop. The method which is a modification of the traditional Green–Ampt infiltration model assumes that ponding of water cannot occur on soil slopes and as a consequence soil in the wetted zone remains partially saturated at the point of slope failure. It differentiates between cases where the initial suction in the slope is high and the rate of infiltration is controlled by the rainfall intensity (supply controlled) and, situations where the suction is low, and the rate of infiltration is controlled by the infiltration capacity of the soil (demand controlled). When applied to a case history where field measurements of infiltration into a slope were available the new method provided a reasonable approximation of the measured infiltration time. [Copyright &y& Elsevier]