Performance of a geogrid reinforced soil wall on PVD drained multilayer soft soils
- Authors: Chen, Jianfeng , Tolooiyan, Ali , Xue, Jianfeng , Shi, Zhenming
- Date: 2016
- Type: Text , Journal article
- Relation: Geotextiles and Geomembranes Vol. 44, no. 3 (2016), p. 219-229
- Full Text: false
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- Description: A geogrid reinforced soil wall was built on Prefabricated Vertical Drain (PVD) improved multilayer soft soils at the end of a road embankment in Shanghai, China. One day after the last loading stage, an arc shaped settlement was observed on the embankment surface with little observable cracks on the side slopes, and sudden increase of pore water pressure was observed in the piezometers installed in the PVD improved zone. A three dimensional finite element analysis was carried out to compare the performance of the wall with PVDs functional and dysfunctional. The comparison supported the assumption that the PVDs may have failed during construction due to bending or kinking of PVDs caused by the large settlement and lateral movement in the ground. The analysis showed that the movement of the wall toe is very sensitive to its location in the cross direction. Therefore attention should be paid while using toe movement as an indication of wall stability. It shows that the failure had mainly taken place in between the shoulders of the embankment rather than the whole wall. For a full slide to develop, pull out or tensile failure may occur in the reinforcements on the side slopes. Large stresses can be generated in the geogrids in the cross embankment direction due to the uneven settlement observed in the ground. Considering this, biaxial geogrid should be considered if the stress is too high and the inclusion of wrap around geogrids on the side slopes may help to increase the integrity and stability of the wall. © 2015 Elsevier Ltd.
Measurement of water pressure properties of unsaturated brown coal using triaxial test
- Authors: Couling, Catherine Elizabeth , Xue, Jianfeng , Tolooiyan, Ali , Mackay, Rae
- Date: 2014
- Type: Text , Conference paper
- Relation: Unsaturated Soils: Research & Applications Vol. 1
- Relation: Proceedings of the 6th International Conference on Unsaturated Soils, UNSAT 2014
- Relation: Sydney, Australia, 2-4 July, 2014
- Full Text: false
- Reviewed:
- Description: Skempton used the B-parameter (see Equation 1) to represent the degree of saturation of a material, such that, B → 0, when the degree of saturation = 0 and, B → 1, when the degree of saturation = 1 Δ Δ Δu B[ (Δ A+ )]σ3 1σ 3 (1) where, Δu is change in pore water pressure, A and B are pore-pressure coefficients, and σ3 and σ1 are minor and major principal stresses.
Measurement of pore water pressure properties of unsaturated brown coal using triaxial test
- Authors: Couling, Catherine Elizaebth , Tolooiyan, Ali , Mackay, Rae , Xue, Jianfeng
- Date: 2014
- Type: Text , Conference paper
- Relation: 6th International Conference on Unsaturated Soils, UNSAT 2014 p. 1531-1535
- Full Text: false
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- Description: Skempton's B parameter characterises the effect of fluid compressibility on the time dependent deformation of materials during isotropic loading. The Skempton B-parameter has been determined for a sample of Victorian brown coal for a range of confining pressures, corresponding to the range of conditions which the coal experiences below the ground water table. The relationship between the change in the B-parameter with respect to time and pressure has also been examined. It has been found that a high back pressure (more than 400 kPa) is required in the material to achieve a degree of saturation close to 100+ACU-. The set of data from these tests is able to provide important evidence of the depth and stress dependent behaviour of the coal.
Geophysical and geotechnical assessment of a railway embankment failure
- Authors: Donohue, Shane , Gavin, Kenneth , Tolooiyan, Ali
- Date: 2011
- Type: Text , Journal article
- Relation: Near Surface Geophysics Vol. 9, no. 1 (2011), p. 33-44
- Full Text: false
- Reviewed:
- Description: A geophysical investigation was carried out after the failure of an important railway embankment in the south-east of Ireland, The embankment, which had a long-term history of stability problems, was studied using a combination of ground-penetrating radar (GPR), electrical resistivity tomography (ERT), multichannel analysis of surface waves (MASW) and geotechnical testing. A significant thickening of the ballast layer around the failure location was observed using GPR, which confirmed the existence of an ongoing stability problem in the area. ERT profiles determined the presence and spatial extent of a significant layer of soft clay both beneath and to the east of the embankment, which could have a major impact on its long-term stability. ERT also detected steeply sloping bedrock close to the failure zone that is likely to have contributed to the long-term settlement of the embankment, which necessitated frequent re-ballasting. MASW confirmed the presence of the steeply sloping bedrock in addition to determining the low stiffness (Gmax) values of the embankment fill. High quality sampling of the soft clay deposit was undertaken and strength and compressibility tests revealed the importance of this layer to both the on-going serviceability problems evident for the original embankment and the stability problems encountered by the remodelled section. © 2010 European Association of Geoscientists & Engineers.
Geophysical and geotechnical assessment of a railway embankment failure
- Authors: Donohue, Shane , Gavin, Kenneth , Tolooiyan, Ali
- Date: 2011
- Type: Text , Journal article
- Relation: Near Surface Geophysics Vol. 9, no. 1 (2011), p. 33-44
- Full Text: false
- Reviewed:
- Description: A geophysical investigation was carried out after the failure of an important railway embankment in the south-east of Ireland, The embankment, which had a long-term history of stability problems, was studied using a combination of ground-penetrating radar (GPR), electrical resistivity tomography (ERT), multichannel analysis of surface waves (MASW) and geotechnical testing. A significant thickening of the ballast layer around the failure location was observed using GPR, which confirmed the existence of an ongoing stability problem in the area. ERT profiles determined the presence and spatial extent of a significant layer of soft clay both beneath and to the east of the embankment, which could have a major impact on its long-term stability. ERT also detected steeply sloping bedrock close to the failure zone that is likely to have contributed to the long-term settlement of the embankment, which necessitated frequent re-ballasting. MASW confirmed the presence of the steeply sloping bedrock in addition to determining the low stiffness (Gmax) values of the embankment fill. High quality sampling of the soft clay deposit was undertaken and strength and compressibility tests revealed the importance of this layer to both the on-going serviceability problems evident for the original embankment and the stability problems encountered by the remodelled section. © 2010 European Association of Geoscientists & Engineers.
Railway earthwork stability assessment using geophysics
- Authors: Donohue, Shane , Gavin, Kenneth , Tolooiyan, Ali
- Date: 2012
- Type: Text , Conference paper
- Relation: Fourth International Conference on Site Characterization p. 1519-1525
- Full Text: false
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- Description: A large portion of the Irish railway network contains earthworks that were poorly constructed mainly because they were built over 100 years ago when scientific understanding of soil behaviour was not nearly as advanced as it is today. Also, engineers involved in the construction of these structures had to work with often unsuitable local materials as sound bulk fill was not able to be transported significant distances. In order to improve the information obtained from site investigation of these poorly constructed earthworks a number of authors have recently suggested complimenting direct geotechnical investigations with a non-invasive geophysical assessment. In addition to providing a review of the factors which cause failure of earthworks, this paper also discusses the capabilities of three geophysical techniques, Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Waves (MASW) for assessing the stability of railway earthworks. Examples of the use of each technique are provided from forensic investigations into railway earthwork slope failures in Ireland.
Prediction and classification for finite element slope stability analysis by random field comparison
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2019
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 109, no. (2019), p. 117-129
- Full Text: false
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- Description: This paper considers probabilistic slope stability analysis using the Random Finite Element Method (RFEM) combined with processes to determine the level of similarity between random fields. A procedure is introduced to predict the Factor of Safety (FoS) of individual Monte Carlo Method (MCM) random field instances prior to finite element simulation, based on random field similarity measures. Previous studies of probabilistic slope stability analysis have required numerous MCM instances to reach FoS convergence. However, the methods provided in this research drastically reduce computational processing time, allowing simulations previously considered too computationally expensive for MCM analysis to be simulated without obstacle. In addition to computational efficiency, the comparison based procedure is combined with cluster analysis methods to locate random field characteristics contributing to slope failure. Comparison measures are presented for slope geometries of an Australian open pit mine to consider the impacts of associated factors such as groundwater on random field similarity predictors, while highlighting the capacity of the similarity procedure for prediction, classification and computational efficiency.
Optimisation of strength reduction finite element method codes for slope stability analysis
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2018
- Type: Text , Journal article
- Relation: Innovative Infrastructure Solutions Vol. 3, no. 1 (2018), p. 1-12
- Full Text: false
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- Description: One of the modern methods for estimating the factor of safety for the stability of slopes is the strength reduction method. In recent times, computer codes have utilised the strength reduction method in conjunction with finite element analysis. This paper explores the implementation of a strength reduction finite element method with FORTRAN and Python codes in conjunction with the computer-aided engineering package Abaqus, incorporating a modified strength reduction definition, allowing for a refinement of the factor of safety search space. The computational efficiency of the modified method is compared with the traditional technique, for both 2D and 3D analysis. The algorithm results are compared for contrasting FEM element types and geometries and benchmarked against proprietary geotechnical finite element solvers.
Probabilistic investigation of RFEM topologies for slope stability analysis
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2019
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 114, no. (2019), p. 1-15
- Full Text: false
- Reviewed:
- Description: The Random Finite Element Method (RFEM) is an increasingly popular tool in geotechnical engineering, especially for analysis of spatial variation and uncertainty in slope stability. Although the method has gained prominence in recent years, topological effects of strong and weak zones and the impact of their locations remain largely unknown. Although numerous potential slip surface realisations can be generated with RFEM, probabilistic failure statistics are often governed by several representative slip surfaces (RSS). In this research, random field similarity methods and clustering techniques are coupled with RFEM slope stability simulation to determine the impact of shear strength spatial patterns on slope failure mechanisms and safety factors. Regions of significance are highlighted within a case study of a Victorian open-cutbrown coal mine, with particular attention given to the effects on the slope failure surface as well the factor of safety. Results are presented of Factor of Safety distributions when particular slip surfaces and clustering constraints are imposed, providing further understanding of the impacts of shear strength characteristics on probabilistic simulation results.
Comparative approaches to probabilistic finite element methods for slope stability analysis
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Simulation Modelling Practice and Theory Vol. 100, no. (2020), p.
- Full Text: false
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- Description: Probabilistic slope stability analyses are often preferable to deterministic methods when soils are inherently heterogeneous, or the reliability of geotechnical parameters is largely unknown. These methods are suitable for evaluating the risk of slope failure by producing a range of potential scenarios for the slope stability factor of safety. Several probabilistic methods including the Point Estimate Method, Monte Carlo Method and Random Finite Element Method, can be combined with the Finite Element technique. In this study, various shear strength distributions are considered for three different probabilistic Finite Element Methods to determine Factor of Safety and Probability of Failure distributions, based on the associated method of slope stability analysis. Results are presented for a case study of an Australian open-cut coal mine, with a range of shear strength parameter distributions for coal and interseam cohesive materials considered. Coal and interseam shear strength parameters are varied independently, to determine the effects of each material on the slope Factor of Safety. © 2019 Elsevier B.V.
An investigation of cross-sectional spatial variation with random finite element method slope stability analysis
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geotechnical and Geological Engineering Vol. 38, no. 6 (2020), p. 6467-6485
- Full Text: false
- Reviewed:
- Description: The selection of two-dimensional cross-sections for plane-strain slope stability analysis often requires a range of assumptions such that the most appropriate cross-section is considered. When faced with complex strata, surface topologies and pore-water pressure distributions, the selection of an appropriate cross-section is non-trivial. Circumstances are further complicated when considering spatially variable soils and heterogeneous strength parameters. In this study, the effects of spatially variable geotechnical parameters are examined for a range of two-dimensional random finite element method (RFEM) simulations of an open-pit mine. A distinct set of random field instances are provided to each cross-section to isolate the impact of geometry and strata variation when coupled with spatially variable soil characterisations. Particular attention is given to the regions providing the greatest impact on factors of safety and representative slip surfaces for each slope geometry, evaluating the need for full three-dimensional RFEM simulation. Further statistical analyses are conducted to establish which random field slope stability cross-sections are significantly different from the underlying cross-section population, thereby identifying the best cross-section to represent the overall slope geometry. © 2020, Springer Nature Switzerland AG.
Bayesian analysis of random finite element method slip surfaces for slope stability
- Authors: Dyson, Ashley , Tolooiyan, Ali
- Date: 2019
- Type: Text , Conference proceedings , Conference paper
- Relation: 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future, YSRM 2019 p. 118-123
- Full Text: false
- Reviewed:
- Description: The Random Finite Element Method (RFEM) is a powerful technique for incorporating spatially variable shear strength parameters with slope stability numerical simulations. In this research, two-dimensional probabilistic analyses of a large open-cut brown coal mine are presented with particular consideration given to slope Factors of Safety (FoS), when faced with highly anisotropic cohesion and friction angle shear strength parameters. Bayesian methods are implemented to determine updated shear strength parameters based on Factors of Safety and Representative Slip Surfaces (RSS) categorizations. By this method, the impact of observed slip surface depths and safety factors is further investigated. Monte Carlo simulation is implemented in the Finite Element environment Abaqus, with an optimised Strength Reduction Method to determine Factors of Safety. Comparisons of conditional shear strength distributions are made for associated slope safety factors and shallow slip surfaces from a cross-section of the Yallourn open-cut brown coal mine, in Victoria, Australia. The updated shear strength distributions provide a greater understanding of the necessary conditions of particular slope failure mechanisms, contributing further understanding of the stability of Victorian brown coal mines. ©2019 Japanese Society for Rock Mechanics
Use of stochastic XFEM in the investigation of heterogeneity effects on the tensile strength of intermediate geotechnical materials
- Authors: Dyson, Ashley , Tang, Zhan , Tolooiyan, Ali
- Date: 2018
- Type: Text , Journal article
- Relation: Finite Elements in Analysis and Design Vol. 145, no. (2018), p. 1-9
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- Description: The numerical simulation of an Unconfined Expansion Test (UET) is presented with tensile strength fracture criteria assigned by stochastic methods to take into account material heterogeneity. Tests are performed by producing radial cavity expansion models of thinly sliced cylindrical specimens. The introduction of element-wise allocation of fracture parameters generates instances of specimen failure without the requirement of predefined fracture zones, permitting discontinuities to form naturally within zones containing weak strength parameters. The parallel application of an in-house Python scripts and eXtended Finite Element Method (XFEM) facilitates the investigation of heterogeneity effects on the tensile strength of intermediate geotechnical materials.
Structural behaviour of an Australian silty clay (Coode Island silt) stabilised by treatment with slag lime
- Authors: Falah, Mahroo , Ranjbar Pouya, Kaveh , Tolooiyan, Ali , Mackenzie, Kenneth
- Date: 2018
- Type: Text , Journal article
- Relation: Applied Clay Science Vol. 157, no. (2018), p. 198-203
- Full Text: false
- Reviewed:
- Description: A microstructural study of Coode Island Silt (CIS), a soft silty clay from the Melbourne area of Australia, stabilised with slag lime is reported. Slag lime is a blend of 80–85 wt% slag, 15 wt% hydrated lime, Ca(OH)2 and 3–8 wt% gypsum CaSO4.2H2O, and is typically used for soil stabilisation in roading applications. The morphologies of several homogeneous mixtures of slag lime and CIS were studied by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), which indicated the formation of the cementitious phases calcium carbonate, calcium silicate hydrate, calcium aluminium silicate hydrate, and calcium aluminium silicate carbonate. The progress of the CIS-slag lime reactions was also investigated by pH measurements. Slag lime was found to very actively promote pozzolanic reactions with CIS, shown by SEM to form crystalline reticular calcium silicate hydrate and other cementitious products. The most effective pozzolanic reactions occurred in a composite containing 12.5 wt% slag lime with CIS and contained the cement mineral ettringite, contributing to its high strength. These composites constitute a new class of materials with excellent potential for construction applications.
Field investigation of the axial resistance of helical piles in dense sand
- Authors: Gavin, Kenneth , Doherty, Paul , Tolooiyan, Ali
- Date: 2014
- Type: Text , Journal article
- Relation: Canadian Geotechnical Journal Vol. 51, no. 11 (2014), p. 1343-1354
- Full Text: false
- Reviewed:
- Description: This paper presents the results of compression and tension load tests performed on a single helical pile installed in dense sand. The pile was instrumented using strain gauges that allowed the shaft and base load resistance to be separated and the distribution of shaft resistance along the pile during the test to be determined. The pile was loaded first in compression, with a maintained load test, followed by a constant rate of penetration load test being performed to assess the effects of creep on the pile’s response to compression loading. The pile was then loaded in tension using a maintained load test procedure. Finite element analyses were performed using Abaqus and these helped to provide additional insights to explain the response of the instrumented pile during loading. The test showed that during compression loading, substantial bearing pressures developed beneath the pile helix, which provided the majority of axial load resistance. During tension loading, uplift pressure mobilized on the helix again provided the majority of axial resistance. The strain gauges suggested that the pile load response to compression loading was ductile. During tension loading, the pile response was brittle. Whilst load tests performed on only one instrumented pile test are presented, the use of instrumentation and finite element analyses allowed important insights into the load–displacement response of helical piles. © 2014, Can. Geotech. J. All right reserved.
An investigation of correlation factors linking footing resistance on sand with cone penetration test results
- Authors: Gavin, Kenneth , Tolooiyan, Ali
- Date: 2012
- Type: Text , Journal article
- Relation: Computers and Geotechnics Vol. 46, no. (2012), p. 84-92
- Full Text:
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- Description: Significant research effort has led to improvements in our ability to estimate the ultimate bearing resistance of footings in sand. These techniques often estimate the footing resistance at relatively large displacements, typically 10% of the footing width, q b0.1. Cone Penetration Test (CPT) design methods typically link q b0.1 and q c through a constant reduction factor, α. A range of α factors for shallow footings have been proposed, some methods suggest that α is constant and while others that it varies with footing width and depth (or stress level). There is a dearth of field data with which to compare these correlation factors, in particular where foundation width and depth have been varied in the same ground conditions. For this reason finite element analyses have proven to be a useful tool for performing the parametric studies required to asses factors controlling α. This paper describes the results of numerical analyses performed to investigate α factors for soil profiles which were calibrated using the results of the CPT tests performed at a dense sand test-bed site. The numerical model was first used to perform parametric analyses to consider the effect of footing width, B and footing depth, D on the α factor mobilised in dense Blessington sand. In order to assess the effects of relative density, footing tests in a range of natural sands with variable in situ densities were modeled. The results of the finite element analyses suggest that a direct correlation between q b0.1 and q c can be established at a given test site which is independent of footing width and depth and is relatively weakly dependent on the sands relative density if the zone of influence of the foundation considered is large enough. © 2012 Elsevier Ltd.
The base resistance of non-displacement piles in Sand. Part I : Field tests
- Authors: Gavin, Kenneth , Cadogan, David , Tolooiyan, Ali , Casey, Patrick
- Date: 2013
- Type: Text , Journal article
- Relation: Proceedings of the Institution of Civil Engineers: Geotechnical Engineering Vol. 166, no. 6 (2013), p. 540-548
- Full Text: false
- Reviewed:
- Description: This paper presents the results of full-scale load tests performed to investigate the end bearing pressure mobilised by continuous flight auger piles installed in sand. In particular, the tests considered the effects of the footing width and, by varying the load test procedure (from maintained load test to constant rate of penetration), allowed quantification of creep effects. By comparing the load test results with in situ test results from cone penetration tests, correlations between the end bearing pressure mobilised at normalised settlement levels of 10% of the footing width and the cone penetration test qc value were studied. For the maintained load tests, these correlations were found to be similar to those used in routine design practice. When creep effects were reduced using constant rate of penetration load testing, the end bearing pressure mobilised was significantly higher than that assumed in normal practice, and it was in keeping with the results of finite-element analyses performed using a soil model that ignored creep. In the final section, the field test results are compared to database pile load tests performed on non-displacement piles in sand.
Sensitivity of the stability assessment of a deep excavation to the material characterisations and analysis methods
- Authors: Ghadrdan, Mohsen , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geomechanics and Geophysics for Geo-Energy and Geo-Resources Vol. 6, no. 4 (2020), p.
- Full Text: false
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- Description: Due to the spatial variability of material characterisations in deep and large scale excavations, stability assessment is often a challenging task. Numerous slope stability analysis methods based on a range of assumptions and principles are implemented in commercial software packages to ease the process of stability assessment of non-homogeneous and multi-layered slopes. However, the selection of a suitable method remains crucial as the application of an unrealistic or unsuitable method may lead to catastrophic consequences. Besides material shear strength parameters, and analysis methods, non-strength characterisations such as permeability and creep can affect the result of slope stability analysis significantly. In this study, the sensitivity of the stability assessment of a deep excavation in Australia to material characterisations such as friction angle, cohesion and permeability and creep is investigated by the use of different formulations and assumptions of the Limit Equilibrium Method (LEM) and the Finite Element Method (FEM) as the two most common slope stability methods. The results show that the stability assessment is highly sensitive to the applied method and assumptions. Moreover, the role of material strength and non-strength parameters and the selection of a suitable constitutive model in slope stability assessment is presented. © 2020, Springer Nature Switzerland AG.
Effect of negative excess pore-water pressure on the stability of excavated slopes
- Authors: Ghadrdan, Mohsen , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geotechnique Letters Vol. 10, no. 1 (Mar 2020), p. 20-29
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- Description: Generation of negative excess pore-water pressure (NEPWP) due to the excavation of saturated soils under undrained conditions and the dissipation that follows over time may result in different short- and long-term slope instability. The NEPWP generated due to excavation gradually decreases towards equilibrium or, in some cases, steady seepage. Hence, total pore-water pressures immediately after excavation are lower than the ultimate equilibrium values, leading to a reduction of the average effective stresses in the slope and subsequently threatening stability in the long term. In this research study, the stability of three benchmark civil and mining excavations has been studied, considering the effects of the generation and dissipation of NEPWP. A series of numerical simulations are conducted to determine the role of in situ stresses and time in NEPWP dissipation as well as the consequent effects on the stability of the excavated slopes. To conduct a realistic time-dependent transient analysis, fully coupled hydro-geomechanical formulation has been employed. Results show that in general, higher removal of stress levels lead to higher NEPWP generation and higher factor of safety values in the short term. Thereafter, the dissipation of NEPWP threatens the long-term stability of the excavation.
Slope stability analysis using deterministic and probabilistic approaches for poorly defined stratigraphies
- Authors: Ghadrdan, Moshen , Dyson, Ashley , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2021
- Type: Text , Journal article
- Relation: Geomechanics and Geophysics for Geo-Energy and Geo-Resources Vol. 7, no. 1 (2021), p.
- Full Text: false
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- Description: The stability of slopes directly affects human lives, the environment, and the economy. Inaccurate geological profiles within numerical slope stability models can lead to potentially catastrophic consequences when model conditions do not appropriately reflect real-life stratigraphy. In cases where localised deposits are prevalent, probabilistic methods are often necessary to accommodate for unknown or poorly defined stratigraphies. Currently, there are no commercial geotechnical software packages that simulate probabilistic constitutive behaviour of materials within finite element methods for large-scale stratigraphic analysis. Instead, commercially available probabilistic methods such as the random limit equilibrium method are incapable of incorporating non-linear constitutive soil behaviour. For this reason, advanced constitutive models are seldom coupled with probabilistically varying soil layers or spatially variable soil parameters. The objective of this research is the implementation of a simplified method for probabilistic stratigraphic analysis within a commercially available FE environment, providing a technique to assess the effects of stratigraphic uncertainty on slope stability. The proposed method is presented, highlighting the impact of localised thin layers of soft material as well as their frequency and location on the slope of an operational open-pit mine. The significance of these stratigraphic effects is presented through a case study of Australia’s second-largest open-pit mine, at which the stability of a collapsed coal slope is analysed. To improve the reliability of the finite element method for slope stability assessment, the Monte Carlo approach has been incorporated to consider varying shear strength distributions for models incorporating advanced constitutive behaviour. Thicker probabilistically generated deposits of silty material resulted in increased slope Factors of Safety. Similarly, greater proportions of silty deposits within a predominantly clayey interseam produced larger safety factors than slopes without localised thin silty layers. Stratigraphic analysis indicated that the Factor of Safety was most sensitive to localised silt layers at depths greater than 83 m below ground level. © 2020, Springer Nature Switzerland AG.