Landslides In Sensitive Clays Research Articles

Prediction of retrogressive landslide in sensitive clays by incorporating a novel strain softening law into the Material Point Method

Sensitive clays, when subjected to large strains, exhibit a unique strain-softening behavior, transforming into a remolded liquid with remarkably low shear strength. When a slope fails, this behavior leads to the remolded clay moving away from its original position, triggering subsequent failures and catastrophic outcomes. To accurately predict such scenarios, it is crucial to incorporate realistic strain-softening characteristics into the constitutive soil model. This paper presents a novel yet practical strain-softening law developed by the authors that effectively captures the post-peak behavior of sensitive clays down to their remolded strength. The softening law is implemented in an elastoplastic Mohr-Coulomb model and incorporated into Anura3D, an open-source software that uses the Material Point Method to simulate large deformations. The constitutive model is calibrated by simulating the stress-strain behavior through direct shear tests conducted at three sensitive clay landslide locations. The accuracy of the overall numerical framework is assessed by predicting the post-failure movements of these landslides. Notably, two of the landslides, Sainte-Monique (1994) and Saint-Jude (2010), have previously been analyzed using other numerical tools, allowing for a comparative analysis with the method presented here. The third landslide, the Saint-Luc-de-Vincennes landslide, representing a composite flow slide and spread, has been numerically simulated for the first time. The post-failure behavior observed in the landslide events is compared with field observations and other numerical analyses. The results show that the MPM models with the proposed strain-softening law can reasonably predict post-failure retrogression and runout distance, which are crucial parameters for determining the risk of landslides in sensitive clays.

Analysis of sensitive clay landslide mechanism and impact pipeline bearing characteristics considering spatial variability

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.

Numerical analysis of downward progressive landslides in long natural slopes with sensitive clay

Landslides occurring in sensitive clay often result in widespread destruction, posing a significant risk to human lives and property due to the substantial decrease in undrained shear strength during deformation. Assessing the consequences of these landslides is challenging and necessitates robust numerical methods to comprehensively investigate their failure mechanisms. While studies have extensively explored upward progressive landslides in sensitive clays, understanding downward progressive cases remains limited. In this study, we utilised the nodal integration-based particle finite element method (N-PFEM) with a nonlinear strain-softening model to analyse downward progressive landslides in sensitive clay on elongated slopes, induced by surcharge loads near the crest. We focused on elucidating the underlying failure mechanisms and evaluating the effects of different soil parameters and strain-softening characteristics. The simulation results revealed the typical pattern for downward landslides, which typically start with a localised failure in proximity to the surcharge loads, followed by a combination of different types of failure mechanisms, including single flow slides, translational progressive landslides, progressive flow slides, and spread failures. Additionally, inclined shear bands occur within spread failures, often adopting distinctive ploughing patterns characterised by triangular shapes. The sensitive clay thickness at the base, the clay strength gradient, the sensitivity, and the softening rate significantly influence the failure mechanisms and the extent of diffused displacement. Remarkably, some of these effects mirror those observed in upward progressive landslides, underscoring the interconnectedness of these phenomena. This study contributes valuable insights into the complex dynamics of sensitive clay landslides, shedding light on the intricate interplay of factors governing their behaviour and progression.

Numerical modelling of downward progressive landslides in sensitive clay

Landslides in sensitive clays are catastrophic events that threaten life and property. When plastic strain occurs in sensitive clays, there is a significant reduction in the undrained shear strength. Consequently, even minor triggers can lead to multiple progressive landslides, causing extensive devastation. Investigating landslides in sensitive clay presents challenges, necessitating robust numerical methods to comprehend failure modes and collapse behaviors, particularly in the post-failure phase. Although several numerical methods have been utilized for simulations, most have primarily focused on upward progressive landslides. In this study, we adopted the nodal integration-based particle finite element method to simulate downward progressive landslides triggered by surcharge loads from an embankment near the crest in sensitive clay on a long slope. We also considered nonlinear strain softening in sensitive clays. The effects of the strain softening rate and strength gradient of the sensitive clay layer on the failure mechanisms and destruction extent were investigated. The simulation results reveal that a downward progressive landslide initiates with a localized flow slide surrounding the embankment and usually involves a combination of various failure modes.

A practical approach for predicting landslide retrogression and run-out distances in sensitive clays

In the present study a novel approach of practical interest is proposed to perform a predictive analysis of the landslides in sensitive clays. Specifically, this approach allows a prediction of the landslide triggering along with the consequent distances of retrogression and run-out. To this end, a simple limit equilibrium solution is proposed to deal with the first two steps (prediction of the landslide triggering and the subsequent retrogression distance). A calculation code based on the material point method (MPM) is instead employed for evaluating the run-out distance of the unstable soil mass that was defined in the previous step. Operative values of the undrained shear strength are also suggested for each of the aforementioned steps. The proposed method is very attractive from a practical viewpoint because it is simple to use, not time-consuming and requires few geotechnical parameters of easy experimental determination as input data. The method is applied successfully to several well-documented case studies available in the literature, demonstrating also its reliability for engineering applications. Three of these landslides are analysed in more detail to illustrate the application of the present method to real cases.

Remoulding energy as a criterion in assessing retrogressive landslides in sensitive clays: a review and its applicability to Eastern Canada

Remoulding energy as a criterion in assessing retrogressive landslides in sensitive clays: a review and its applicability to Eastern Canada

Analysis of a landslide in sensitive clays using the material point method

Slope movements are generally classified into four different phases: pre-failure, failure, post-failure and eventual reactivation. In engineering applications, the pre-failure and failure phases are usually analysed using traditional numerical techniques, such as the finite-element method and the finite-difference method. However, these methods are often based on the assumption of small deformations and consequently are unsuitable for analysing the slope behaviour during the post-failure stage, which is usually characterised by very large deformations. To overcome this shortcoming, the material point method (MPM) is employed in the present study. Specifically, MPM is used to perform an analysis of a landslide in sensitive clays that occurred at Saint-Jude (Quebec, Canada) in 2010. To assess the accuracy of the analysis, the final profile and the displacement magnitude detected after the event are compared with those obtained by the numerical simulation. The results provided by MPM are in satisfactory agreement with field observations. The failure mechanism and the development of the failure surface within the slope are also reproduced successfully. These results also show that MPM is an attractive method for analysing the kinematics of landslides in sensitive clays, requiring also a limited number of conventional geotechnical parameters as input data.

Surface displacement expression of progressive failure in a sensitive clay landslide observed with long-term UAV monitoring

Surface displacement expression of progressive failure in a sensitive clay landslide observed with long-term UAV monitoring

A nonlocal Eulerian-based finite-element approach for strain-softening materials

The dependency of finite element (FE) results on mesh size is a major concern for the numerical analysis of strain-softening materials. The local methods of strain regularization rely on the shear strains of a solitary point. However, the nonlocal methods incorporate strain-softening, including the strain in surrounding soil elements, which show less mesh dependency. Previously, nonlocal methods were mostly implemented in Lagrangian-based FE programs and simulated the response for small to moderate strain levels. However, many geotechnical problems, such as large-scale landslides in sensitive clays, involve extremely large deformation. This study presents the implementation of the “original” and two modified nonlocal methods in a Eulerian-based large deformation FE program using a relatively simplified approach where simple soil models, such as von-Mises criteria for undrained behaviours, can be used. Two biaxial compression tests are simulated by using the nonlocal Eulerian-based FE program, and the results are compared with a nonlocal Lagrangian-based FE analysis and a nonlocal Material Point Method (MPM) of simulation, respectively. Among the three, the modified nonlocal methods, especially the over-nonlocal method, show a better performance in mesh convergence analysis. Several approaches have been proposed to minimize the computational costs, as nonlocal modelling is generally computationally expensive.

Stratigraphic profiling, slip surface detection, and assessment of remolding in sensitive clay landslides using the CPT

A multi-year cone penetration testing program was conducted at a landslide subject to episodic retrogression in Mud Creek, Ottawa, to assess whether a hand-operated mobile cone penetration test (CPT) could yield new insights into the current degree of remolding under progressive failure in metastable areas of a landslide where conventional tracked rigs are unable to gain access. The mobile CPT rig permitted tests to be performed through the entire thickness of the Champlain Sea deposit at a penetration rate of 0.5 cm/s, with similar results to tests performed at the standard 2 cm/s. Measurements of pore pressure varied considerably with cone size, with the magnitude of pore pressure response decreasing with cone size. The elevation of the slip surface was identified in the tip resistance as the point of transition between the remolded soil above the slip surface and the intact soil below the slip surface, whereas a further 0.5 m of penetration was required to elevate pore pressures to values indicative of the intact soil behaviour. In situ measurements of shear strength of corresponding layers between the intact and remolded profiles to be compared indicated that the soil above the slip surface had remolded to 50% of its fully remolded strength.

Modeling of Initial Stresses and Seepage for Large Deformation Finite-Element Simulation of Sensitive Clay Landslides

AbstractGroundwater seepage and an increased lateral earth pressure coefficient at rest (K0) increase the potential for triggering large-scale landslides in sensitive clays. After the failure is tr...

GIS based assessment of rainfall-induced landslide susceptibility of sensitive marine clays: a case study

ABSTRACT Landslides are frequent occurrences in Ottawa, Canada because sensitive marine clays (also known as Leda clay or Champlain Sea clay) dominate the landscape. These landslides are often triggered by rainfall in the region. A geographic information system (GIS) based modelling approach has been developed to assess and predict rainfall-induced landslides in the sensitive clays of the Ottawa region. The Transient Rainfall Infiltration and Grid-based Slope-stability (TRIGRS) model has been used in a GIS framework to investigate the influence of rainfall On shallow landslides over the Ottawa region, with respect to time and location. The assessment result maps show that the steep slopes of sensitive clays are more prone to landslides. Furthermore, susceptibility to landslides in these areas increases with long periods of intense rainfall. The proposed GIS based model is validated by comparing the predicted areas of landslides induced by rainfall with previous shallow landslides that had occurred in the Ottawa region. The results show that there is a good agreement between the predicted areas of landslides and the previous landslides reported. The proposed GIS–TRIGRS combined modelling approach can be therefore considered as a potential tool for assessing and predicting rainfall induced landslides in sensitive marine clays in Ottawa.

Modelling of mobility of Rissa landslide and following tsunami

Landslides in sensitive clays pose a major threat to life, property and the environment. The lack of warning signs and the extreme mobility of quick clays increase the risk. When occurring along fjords, lakes or large rivers, the landslides can generate destructive tsunamis. Historical records show that 45% of the shoreline landslides in marine sediments in Norway triggered tsunamis with run-up height of 1 to 15 m. To improve the management of the hazard and risk due to landslides in sensitive materials, the profession needs to develop tools for modelling the mobility of landslides and their tsunamigenic potential. The paper back-calculates the 1978 Rissa landslide, one of the largest quick clay landslides in Norway. Because of the quantity of data available, the Rissa landslide provides a unique benchmark to study the mobility of the quick clay, and the tsunami following the landslide. The paper describes a new approach to model landslide mobility and tsunami run-up, and presents the results of the analyses and a comparison of the results with the observations. The back-calculated mobility (runout distance, flow velocity and debris thickness) and wave run-up on the lakeshore agreed well with the measurements.

Geotechnical centrifuge modelling of retrogressive sensitive clay landslides

Sensitive clay landslides represent a significant geohazard due to their well-known potential for extensive retrogressive failures, on the scale of multiple hectares, which could encompass surrounding communities and infrastructure. Interpretation of retrogression mechanisms is often limited as only forensic investigations are possible. This work presents the results of a physical modelling study to examine retrogressive failures, analysis of each failure episode, and interpretation of the results using published relationships. Five novel centrifuge model tests were conducted under a defined range of undrained shear strength and slope angle conditions. The models are constructed of a sensitive cement–soil mixture that allows for a consistent contractile material with bespoke shear strength. Results indicate the observed retrogression distance correlates with Taylor’s stability number. The addition of a 5° slope angle to invoke a static shear stress on the model provoked notably larger retrogression distances. Post-test undrained shear strength measurements quantified softening of the material along the failure surface. Stability analyses on each failure episode captured the observed failure geometry and factor of safety. Results indicate that the geometric parameters of a slope, specifically the slope angle, may be able to explain a component of the scatter for relating Taylor’s stability number with retrogression distances.

Effects of geometry and soil properties on type and retrogression of landslides in sensitive clays

Flowslide and spread are two common types of landslides in sensitive clays. Empirical criteria, based on single or multiple soil properties and slope geometry, have been proposed for a rough assessment of potential landslide type and retrogression distance. A large variation has been found in the comparison of retrogression distance between empirical equations and field data. In the present study, flowslides and spreads are simulated using a Eulerian-based large-deformation finite-element (FE) method. In addition to strain-softening, a strain-rate-dependent undrained shear strength model that elevates the strain rate effects on the shear strength of liquefied clay flowing at high speed is used. In flowslides, a higher rate of increase in undrained shear strength with depth reduces the depth of subsequent slides, and thereby the retrogression distance. The maximum retrogression occurs for a uniform shear strength profile. The increase in the ratio of horizontal to vertical stress, resistance to downslope movement of the debris and decrease in soil brittleness and slope steepness change the failure pattern from a flowslide to a spread.

Simulating retrogressive slope failure using two different smoothed particle finite element methods: A comparative study

Various smoothed particle finite element methods (SPFEMs) have been developed to simulate large deformation problems, but their efficiency and accuracy in simulating progressive landslides in sensitive clays have remained unclear. In this study, a series of numerical analyses are carried out to investigate the development of retrogressive landslides by two SPFEMs (an edge-based strain smoothing PFEM, ESPFEM, and a node-based strain smoothing PFEM, NSPFEM) in view of their outstanding performance in large deformation analysis. A strain-softening Mohr–Coulomb (MC) model is adopted to simulate the behaviour of sensitive clays during landslide, assuming a Poisson's ratio of 0.49 to ensure undrained conditions. The influence of mesh density on the development of retrogressive failure is evaluated for two SPFEMs. Numerical analyses of three mesh sizes (0.2 m, 0.15 m and 0.12 m) are carried out sequentially, with all results demonstrating that (1) the spread retrogressive landslides with horsts and grabens can be achieved by both SPFEMs with the adopted soil model, (2) run-out and retrogression distances decrease as mesh density increases for both methods, (3) retrogressive collapse occurs earlier for ESPFEM but is delayed for NSPFEM with increased mesh density, (4) NSPFEM allows faster calculations and reduces mesh dependency problems when compared with ESPFEM and (5) the increase of shape factor can accelerate retrogressive evolution of landslides. Finally, a real landslide in sensitive clay at Sainte-Monique, Quebec, is simulated to demonstrate ESPFEM's computational efficiency and accuracy.

Overview of Retrogressive Landslide Risk Analysis in Sensitive Clay Slope

Sensitive clays are known for producing retrogressive landslides, also called spread or flowslides. The key characteristics associated with the occurrence of these landslides on a sensitive clay slope must be assessed, and the potential retrogressive distance must be evaluated. Common risk analysis methods include empirical methods for estimating the distance of potential retrogression, analytical limit equilibrium methods, numerical modelling methods using the strength reduction technique, and the integration of a progressive failure mechanism into numerical methods. Methods developed for zoning purposes in Norway and Quebec provide conservative results in most cases, even if they don’t cover the worst cases scenario. A flowslide can be partially analysed using analytical limit equilibrium methods and numerical methods having strength reduction factor tools. Numerical modelling of progressive failure mechanisms using numerical methods can define the critical parameters of spread-type landslides, such as critical unloading and the retrogression distance of the failure. Continuous improvements to the large-deformation numerical modeling approach allow its application to all types of sensitive clay landslides.

On casting clay specimens of bespoke shear strength and sensitivity for landslide modelling

Sensitive clay landslides are a geohazard often exhibiting flow-like retrogressive behaviour. Soils with high sensitivity experience significant strain softening − a key characteristic of these types of slope movements. In this paper, an experimental method using high early strength cement mixed with clay soil is investigated to cast repeatable samples of a bespoke shear strength and sensitivity while reducing specimen preparation time. The addition of cement bonds from hydration reactions was observed to encourage the development of a metastable soil structure with sufficiently high moisture content to exhibit both a high peak strength and a low remoulded strength. Various cement and water content mixtures were examined, with either kaolin clay or a naturally sensitive clay from Mud Creek, Ontario and Portland type 1 or type 3 cement. Undrained shear strength testing was measured with the Swedish fall cone and the miniature lab vane. Soil−cement mixtures developed shear strength of up to 60 kPa with sensitivities from 4 to 16 within a 7 d curing time. This paper reports lessons learned from the mixing, curing and testing of the sensitive material, as well as the results from a geotechnical centrifuge experiment examining retrogressive sensitive clay landslides.

Geotechnical investigations of an earthquake that triggered disastrous landslides in eastern Canada about 1020\u2009cal BP

Geotechnical studies are carried out to investigate the location and magnitude of a prehistoric earthquake in eastern Canada. Previous studies identified 12 sensitive clay landslides of about 1020 cal BP in the Ottawa-Gatineau region, including one of the most disastrous slope failures in eastern Canada. The landslides were hypothesized to have been triggered by an earthquake. In the current study, three of those landslides are investigated to understand their failure mechanisms. The study sites form a triangle of lateral distances of about 38, 38 and 35 km. Micro-seismic surveys, cone penetrometer tests, vane shear tests, soil sampling and laboratory testing are conducted to collect geotechnical data. Slope stability models are constructed to calculate threshold ground accelerations required to trigger the landslides. The ground accelerations are used with Ground-Motion Prediction Equations to triangulate the earthquake. The results indicate an earthquake of a minimum moment magnitude of 5.9 near Eardley, Quebec.

A case study and implication: particle finite element modelling of the 2010 Saint-Jude sensitive clay landslide

Modelling of landslides in sensitive clays has long been recognised as a challenge. The strength reduction of sensitive clays when undergoing plastic deformation makes the failure proceed in a progressive manner such that a small slope failure may lead to a series of retrogressive failures and thus to an unexpected catastrophic landslide. The clay in the entire process may mimic both solid-like (when it is intact) and fluid-like (when fully remoulded, especially for quick clays) behaviours. Thereby, a successful numerical prediction of landslides in sensitive clays requires not only a robust numerical approach capable of handling extreme material deformation but also a sophisticated constitutive model to describe the complex clay behaviour. In this paper, the particle finite element method (PFEM) associated with an elastoviscoplastic model with strain softening is adopted for the reconstruction of the 2010 Saint-Jude landslide, Quebec, Canada, and detailed comparisons between the simulation results and available data are carried out. It is shown that the present computational framework is capable of quantitatively reproducing the multiple rotational retrogressive failure process, the final run-out distance and the retrogression distance of the Saint-Jude landslide. Furthermore, the failure mechanism and the kinematics of the Saint-Jude landslide and the influence of the clay viscosity are investigated numerically, and in addition, their implications to real landslides in sensitive clays are discussed.