Laureate Professor Scott Sloan

© 2016, Springer-Verlag Wien. This study aims at providing quality experimental data on the effects of temperature on tensile strength and small strain shear stiffness of two Australian mudstones. The objective is to provide multiscale data in view of developing a numerical model that can capture and simulate the complex multiphysics of underground coal fire propagation. Two mudstones were collected in the Hunter Valley, close to a known underground coal fire, referred to as ¿Burning Mountain.¿ The rock specimens were heated to a range of temperatures (maximum of 900¿°C) for 24¿h, and the materials were comprehensively characterized by X-ray diffraction, thermal gravimetric analyses, optical microscopy and scanning electron microscopy. In addition, mercury intrusion porosimetry was used in order to track changes in pore size distribution with temperature. Investigations at microscale were complemented by testing at the macroscale. In particular, the paper focuses on the evolution of the tensile strength and small strain shear stiffness as the materials are subjected to heating treatment. Results show that both parameters evolve in a non-monotonic manner with temperature. The observed mechanical responses are fully explained and corroborated by microstructural observations.

© Springer-Verlag Berlin Heidelberg 2016. In this paper, the incremental problem for consolidation analysis of elastoplastic saturated porous media is formulated and solved using second-order cone programming. This is achieved by the application of the Hellinger-Reissner variational theorem, which casts the governing equations of Biot¿s consolidation theory as a min-max optimisation problem. Themin-max problem is then discretised using the finite element method and converted into a standard second-order cone programming problem that can be solved efficiently using modern optimisation algorithms (such as the primaldual interior-point method). The proposed computational formulation is verified against a number of benchmark examples and also applied to simulate the construction of a road embankment on soft clay.

© 2016 Elsevier Ltd. The development of a numerical procedure for the finite element analysis of anchors dynamically penetrating into saturated soils is outlined, highlighting its unique features and capabilities. The mechanical behaviour of saturated porous media is predicted using mixture theory. An algorithm is developed for frictional contact in terms of effective normal stress. The contact formulation is based on a mortar segment-to-segment scheme, which considers the interpolation functions of the contact elements to be of order N, thus overcoming a numerical deficiency of the so-called node-to-segment (NTS) contact algorithm. The nonlinear behaviour of the solid constituent is captured by the Modified Cam Clay soil model. The soil constitutive model is also adapted so as to incorporate the dependence of clay strength on strain rate. An appropriate energy-absorbing boundary is used to eliminate possible wave reflections from the artificial mesh boundaries. To illustrate the use of the proposed computational scheme, simulations of dynamically penetrating anchors are conducted. Results are presented and discussed for the installation phase followed by 'setup', i.e., pore pressure dissipation and soil consolidation. The results, in particular, reveal the effects of strain rate on the generation of excess pore pressure, bearing resistance and frictional forces. The setup analyses also illustrate the pattern in which pore pressures are dissipated within the soil domain after installation. Hole closure behind a dynamic projectile is also illustrated by an example.

© 2015 Elsevier Ltd. Pile load tests are used to refine designs and for quality assurance. They can also be used to verify the reliability of piles and pile groups. Stochastic methods have previously been developed to verify the reliability of single piles. A general stochastic method to verify the reliability of pile groups is developed in this paper. The method can be used to assess the reliability of groups where pile tests have been conducted to the ultimate capacity, to below the ultimate capacity but exceeding specified capacity, and where pile tests fail to achieve the specified capacity. In the latter case, the method allows decisions to be made as to whether the reliability of the entire pile group is satisfactory or whether additional piles need to be installed.

© 2016 Elsevier Ltd. The time and strain rate dependency observed in natural soft clays is formulated within the framework of conventional elastoplasticity. Creep of soft clays is essentially like the response of an overdamped oscillatory system, i.e., the strain rate decays in an exponential manner. A characteristic strain rate and time relationship is presented based on data from creep tests on a large number of different soft clays. The evolutionary change of strain rate is found to affect the mechanical response of soft clays in an isotach manner. Taking strain rate as another stress-like variable, a loading-isotach (LI) yield curve is proposed, which describes the combined hardening mechanisms of loading and variation of strain rate. Incorporation of this LI yield curve into critical state soil mechanics results in an isotach elastoplastic (IEP) model in triaxial stress-strain-strain rate space, which has been dubbed 'Hunter Clay'. The effects of fabric anisotropy and inter-particle cementation, which are typical features of natural soft clays, are also introduced to produce an advanced hierarchical constitutive model for soft clay. Qualitative predictions are first described and compared with the characteristic behaviour of natural soft clays. Experimental validations using test data for two soft clays are then carried out, and comparisons of the model predictions and experimental data demonstrate the capability of the model in reproducing realistic behaviour of natural soft clays. This work confirms that the complex mechanical behaviour of natural soft clays can be reproduced satisfactorily within the general framework of classical plasticity theory.

Copyright © 2016 John Wiley & Sons, Ltd. This paper presents a 3D formulation for quasi-kinematic limit analysis, which is based on a radial point interpolation meshless method and numerical optimization. The velocity field is interpolated using radial point interpolation shape functions, and the resulting optimization problem is cast as a standard second-order cone programming problem. Because the essential boundary conditions can be only guaranteed at the position of the nodes when using radial point interpolation, the results obtained with the proposed approach are not rigorous upper bound solutions. This paper aims to improve the computing efficiency of 3D upper bound limit analysis and large problems, with tens of thousands of nodes, can be solved efficiently. Five numerical examples are given to confirm the effectiveness of the proposed approach with the von Mises yield criterion: an internally pressurized cylinder; a cantilever beam; a double-notched tensile specimen; and strip, square and rectangular footings. Copyright © 2016 John Wiley & Sons, Ltd.

© 2016, Springer-Verlag Berlin Heidelberg. We investigate numerically the mechanism governing the quasi-static collapse of two-dimensional granular columns using a recently proposed continuum approach, the particle finite element method (PFEM), which inherits both the solid mathematical foundation of the traditional finite element method and the flexibility of particle methods in simulating ultra-large deformation problems. The typical collapse patterns of granular columns are reproduced in the PFEM simulation and the physical mechanism behind the collapse phenomenon is provided. The collapse processes obtained from the PFEM simulation are compared to experimental observations and discrete element modeling, where a satisfactory agreement is achieved. The effects of the macro density and friction angle of the granular matter, as well as the roughness of the wall surfaces on the quasi-static collapse, are also investigated in this paper. Furthermore, our simulations reveal new quasi-static collapse patterns, as supplements to the ones already observed in the experimental tests, due to the change of the roughness of the basal surface.

© 2016, Springer-Verlag Berlin Heidelberg. This paper presents a comprehensive experimental investigation on time-dependent swelling behaviour at both macroscale and microscale of a natural Australian expansive soil in compacted state. A number of one-dimensional swelling tests under different vertical pressures, different initial void ratios and initial water contents were performed. The characterization at macroscale was complemented by extensive microstructural investigations through mercury intrusion porosimetry and scanning electron microscope observation on both as-compacted and swollen specimens. The results were discussed at two different scales within a framework of double-porosity, which was finalized by linking the macrostructural¿microstructural strains ratio with secondary swelling/compression coefficients. The multi-scale correlation appears to be largely independent of the specimen initial conditions. The study showed that the secondary swelling and primary swelling are governed by the same factors and that secondary swelling takes place mainly in macropores, of which the change magnitude depends on the level of confinement applied. The microstructural investigations show that swelling is accompanied by significant microfabric changes.

Copyright © 2016 John Wiley & Sons, Ltd. Various analytical theories of consolidation for soils with vertical drains have been proposed in the past. Most conventional theories are based on a cylindrical unit cell that contains only a single vertical drain. This paper described a new analytical model where a vertical drain located at the centre (the ¿inner vertical drain¿) and is surrounded by two or three vertical drains (the ¿outer vertical drains¿), the number of which depends on whether the configuration is triangular or rectangular. Both types of drains are combined into a cylindrical unit cell, and the water is assumed to flow both inwards to the inner vertical drain and outwards to the outer vertical drains distributed around the circumference. The outer radial boundary of the unit cell is regarded as a permeable boundary, with a drainage capacity of two or three separate vertical drains for triangular and rectangular configurations, respectively. The smear effects and the drainage resistances for both the inner and outer vertical drains are considered in the analysis as well. In this way, the equations governing the consolidation process with multiple vertical drains are derived, and the corresponding analytical solutions are obtained for instantaneously loading, ramp loading and multi-stage of instantaneously loading and multi-stage of ramp loading. The present solutions are finally compared with several conventional solutions for a single vertical drain in the literature. The results show that the present model predicts the same average degree of consolidation as conventional models do, which verifies the correctness of this new model. Finally, the settlement predicted by the present solution is compared with the measured settlement from a field test at the Port of Brisbane, Australia, which shows a good agreement between them. Copyright © 2016 John Wiley & Sons, Ltd.

© 2016 This paper presents an analytical solution and numerical simulation of vacuum consolidation beneath a circular loading area (e.g. circular oil tanks or silos). The discrete system of vertical drains is substituted by continuous concentric rings of equivalent drain walls. The effectiveness of the vacuum as distributed along the drain length and the well resistance of the drains are considered. A rigorous solution of radial drainage towards cylindrical drain walls is presented and compared to numerical FEM predictions. The model is then successfully adopted to analyse the vacuum consolidation of a circular embankment in the Ballina field testing facility in Australia.

© 2016 Elsevier Ltd The paper proposes an efficient method of drift correction in explicit stress integration schemes. The new method does not require significant changes to existing implementations and may, in fact, be regarded as a streamlining modification to standard drift correction schemes which may be used in tandem.

© 2015 John Wiley & Sons, Ltd. A finite element algorithm for frictionless contact problems in a two-phase saturated porous medium, considering finite deformation and inertia effects, has been formulated and implemented in a finite element programme. The mechanical behaviour of the saturated porous medium is predicted using mixture theory, which models the dynamic advection of fluids through a fully saturated porous solid matrix. The resulting mixed formulation predicts all field variables including the solid displacement, pore fluid pressure and Darcy velocity of the pore fluid. The contact constraints arising from the requirement for continuity of the contact traction, as well as the fluid flow across the contact interface, are enforced using a penalty approach that is regularised with an augmented Lagrangian method. The contact formulation is based on a mortar segment-to-segment scheme that allows the interpolation functions of the contact elements to be of order N. The main thrust of this paper is therefore how to deal with contact interfaces in problems that involve both dynamics and consolidation and possibly large deformations of porous media. The numerical algorithm is first verified using several illustrative examples. This algorithm is then employed to solve a pipe-seabed interaction problem, involving large deformations and dynamic effects, and the results of the analysis are also compared with those obtained using a node-to-segment contact algorithm. The results of this study indicate that the proposed method is able to solve the highly nonlinear problem of dynamic soil-structure interaction when coupled with pore water pressures and Darcy velocity.

Copyright © 2016 John Wiley & Sons, Ltd. This paper studies the behaviour of the error incurred when numerically integrating the elasto-plastic mechanical relationships of a constitutive model for soils using an explicit substepping formulation with automatic error control. The correct update of all the variables involved in the numerical integration of the incremental stress¿strain relationships is central to the computational performance of the integration scheme, and, although often missed in the literature, all variables (including specific volume) should be explicitly considered in the algorithmic formulation. This is demonstrated in the paper by studying, in the context of the Cam clay formulations for saturated soils, the influence that the updating of the specific volume has on the accuracy of the numerical solution. The fact that the variation of the local error with the size of the integrated strain depends on the order of local accuracy of the numerical method is also used in the paper to propose a simple and powerful strategy to verify the correctness of the implemented mathematical formulation. Copyright © 2016 John Wiley & Sons, Ltd.

© 2015 Elsevier Ltd. This paper presents an analytical method to compute the dynamic response of a thin-walled pipe pile due to a vertical transient point load acting on its head. Inspired from challenges faced during the interpretation of low-strain integrity tests on pipe piles, the proposed method moves beyond the widely used one-dimensional wave theory to consider the asymmetric nature of the problem, and stress wave propagation along both the vertical and circumferential directions. Coupling of pipe pile-viscoelastic soil vibration is considered via modeling the outer and inner soil as a series of infinitesimally thin layers in perfect contact with the pile, and their low-strain properties are directly introduced in the solution. The methodology is validated against numerical results, before discussing the mechanisms governing the dynamic response of the pipe pile-soil system to the impact load, with emphasis on the vertical velocity measured at a hypothetical receiver placed on the pile head. Additional results from a parametric analysis are used to provide insights on the accurate estimation of the arrival time of the receiving wave, and the optimal location of the receiver.

Copyright © 2015 Published by Elsevier B.V. All rights reserved. Industrial wastewaters often consist of a complex chemical cocktail with treatment of target contaminants complicated by adverse chemical reactions. The impact of metal ions (Cd^{2 +}, Ba^{2 +} and Mn^{2 +}) on the kinetics of fluoride removal from solution by natural zeolite was investigated. In order to better understand the kinetics, the pseudo-second order (PSO), Hill (Hill 4 and Hill 5) and intra-particle diffusion (IPD) models were applied. Model fitting was compared using the Akaike Information Criterion (AIC) and the Schwarz Bayesian Information Criterion (BIC). The Hill models (Hill 4 and Hill 5) were found to be superior in describing the fluoride removal processes due to the sigmoidal nature of the kinetics. Results indicate that the presence of Mn (100 mg L^{- 1}) and Cd (100 mg L^{- 1}) respectively increases the rate of fluoride sorption by a factor of ~ 28.3 and ~ 10.9, the maximum sorption capacity is increased by ~ 2.2 and ~ 1.7. The presence of Ba (100 mg L^{- 1}) initially inhibited fluoride removal and very poor fits were obtained for all models. Fitting was best described with a biphasic sigmoidal model with the degree of inhibition decreasing with increasing temperature suggesting that at least two processes are involved with fluoride sorption onto natural zeolite in the presence of Ba. Crown

© 2015. A comprehensive numerical study on finite element implementation of hypoplastic models is presented. Two crucial aspects, local integration of the constitutive equations (the local problem) and forming tangent operators for Newton-Raphson iteration (the global problem), are investigated. For solving the local problem, different integration algorithms, including explicit and implicit methods, are examined using tri-axial compression tests and incremental stress response envelopes, as well as typical boundary value problems. For solving global problems, three different ways of generating the tangent operator are compared. The numerical evidences indicate that, in terms of accuracy, efficiency and robustness, explicit methods with substepping and error control are the best choices for constitutive integration of hypoplastic models while the so-called continuum tangent operators have certain advantages over two other types of numerically-generated consistent tangent operators.

© 2014 John Wiley & Sons, Ltd. The first part of the paper presents a material point method solution for the bearing capacity of a deep foundation in purely cohesive soil, which is a widely known engineering problem. The results computed with the generalised interpolation material point method are compared to the results obtained previously with an advanced limit analysis code. The second part of the paper shows material point method simulations of collapsing piles of granular material and compares the results with experimental observations from the literature. The problems considered are problematic to solve using the displacement finite element method as they generally include very large deformations.

© 2015 Elsevier Ltd. The mechanical properties of dry soil mix (DSM) columns can be highly variable. Variability can be accounted for in the construction specification for deterministic design and directly in reliability based design. Design methods and specifications to date adopt simplifications that do not take the variability of the columns fully into account. This paper uses both simple and advanced probabilistic methods to assess the performance/failure and system redundancy of dry soil mix columns. Reliability-based design methods and examples are given for the design of column strength and the adjustment of the column spacing to achieve a target probability of unacceptable performance or failure. An acceptance criteria chart is developed. The pull-out resistance tests on the DSM columns constructed for the Ballina Bypass motorway construction project in NSW Australia are compared to the chart to provide guidance with respect to acceptance criteria required to achieve the desired performance.

© 2015 American Physical Society. We investigate numerically the mechanisms governing horizontal dragging of a rigid cylinder buried inside granular matter, with particular emphasis on enumerating drag and lift forces that resist cylinder movement. The recently proposed particle finite element method is employed, which combines the robustness of classical continuum mechanics formulations in terms of representing complex aspects of the material constitutive behavior, with the effectiveness of discrete element methods in simulating ultralarge deformation problems. The investigation focuses on the effect of embedment depth, cylinder roughness, granular matter macromechanical properties, and of the magnitude of the cylinder's horizontal displacement on the amplitude of the resisting forces, which are discussed in light of published experimental data. Interpretation of the results provides insight on how the material flow around the cylinder affects the developing resistance, and a mechanism is proposed to describe the development of a steady-state drag force at large horizontal movements of the cylinder.

© 2015 Elsevier Ltd. Experimental data on Lower Cromer Till (LCT), a sandy silty-clay, are re-evaluated enabling a study on the effects of plastic anisotropy of soil fabric. The results of virgin constant stress ratio consolidation tests reveal that an equilibrium state is achieved and maintained under any specific radial loading path, with characteristics of a unique anisotropic fabric and a unique straining mode. The inclination of the plastic dilatancy and the yield surface from the hydrostatic axis provides a means of quantifying this equilibrium state of the soil fabric. A unique fabric anisotropy at critical state is naturally obtained. Rotational hardening laws are then proposed to quantify the changes in plastic anisotropy of soil fabric for all stress ranges. Constitutive relations are formulated within the framework of Critical Sate Soil Mechanics, with a non-associated flow rule logically determined from experiments. The proposed rotational hardening laws have been systematically validated against a large bank of laboratory tests on LCT samples, covering a variety of deposition conditions, stress histories, and overconsolidation ratios. Comparisons illustrate the feasibility and efficiency of the proposed framework in describing the plastic anisotropy of LCT, which may suggest possible application to other types of clays.

© 2014 Elsevier Ltd. The consolidation behavior of ground with vertical drains is known to be greatly affected by the finite permeability of the sand drains, also called the effect of well resistance. However, up to now, no analytical methods have been reported for evaluating this effect on the nonlinear consolidation behavior of vertical drains. In this paper, by considering the nonlinear compressibility and permeability of soil during consolidation, the effect of well resistance was incorporated into the derivation of the equations that govern the nonlinear consolidation of a vertical drain with coupled radial-vertical flow. In addition, the smear effect was considered by assuming three decay patterns for the radial permeability coefficients of the soil toward the sand drain in the smeared zone. After obtaining the governing equations, a simplified analytical solution is derived for a general time-variable surcharge loading. Based on the general solution obtained, detailed solutions are provided for three special types of loading schemes: constant loading, single-stage loading, and multi-stage loading. The validity of the solution is verified by reducing it to several special cases and comparing these to existing solutions. Finally, the effect of the well resistance, the ratios of the compression index to the radial and vertical permeability indices, various loading schemes, and various variation patterns of the radial permeability coefficient of the soil in the smeared soil zone are investigated using parametric analysis.

© 2015 Elsevier Ltd. All rights reserved. Groundwater contaminated with spent pot liner leachate (SPLL) was treated with calcite (CaCO3) and CO2 in a series of free drift batch reactor kinetic experiments with the aim of optimizing fluoride removal. In order to better understand the reaction kinetics for SPLL, the pseudo-second order (PSO), four and five parameter Hill (Hill 4 & Hill 5) models were applied to observed fluoride removal as a function of CO2 partial pressure and stirring rate. To account for differences in the number of model parameters, model fitting was compared using the Akaike information criterion (AIC), the Schwartz Bayesian information criterion (BIC) and the statistical F-test. In every case, the best fitting model order was found to be Hill 5 > Hill 4 > PSO due to the ability of the Hill models to accommodate sigmoidal kinetics. Removal of fluoride from SPLL under atmospheric CO2 conditions was found to be inhibited with no removal occurring for the first 3000 min with the inhibition times, based on the reaction half-life, reducing with increased CO2 partial pressure and stirring rate. X-ray diffraction (XRD) analysis revealed that the residual solid filtrate consisted of trona (Na3(CO3)(HCO3)·2H2O) a potentially valuable mineral kogarkoite (Na3SO4F) and fluorite (CaF2) accounting for fluoride removal, and unreacted calcite (CaCO3).

© 2015, Thomas Telford Services Ltd. All rights reserved. In practical geotechnical engineering the factor of safety is still determined by means of simple limit equilibrium analysis in many cases. However, because displacement finite-element analysis is routinely applied for assessing displacements and stresses for working load conditions, this technique is increasingly being used to calculate ultimate limit states and, consequently, factors of safety, usually by means of the so-called strength reduction technique, and results which are comparable to those obtained with limit equilibrium methods have been reported in the literature. However, owing to the inherent assumptions of limit equilibrium analyses, they do not always provide unique factors of safety. The purpose of this paper is on the one hand to compare the strength reduction method with rigorous limit analyses which are based on collapse theorems of plasticity, and on the other hand to investigate if a shortcoming of the strength reduction method, namely possible numerical instabilities for non-associated plasticity, can be overcome. Two examples are considered, namely slope stability and tunnel face stability. Finally an important note on the definition of the factor of safety for effective and total stress analysis under undrained conditions is provided.

© 2015 Elsevier Ltd. Slope stability analyses in practical geotechnical engineering are predominantly performed using limit equilibrium methods, despite the inherent shortcoming that the form of the failure mechanism has to be defined a priori. This assumption is not needed when more advanced methods, such as limit analyses or displacement-based finite element methods, are employed for calculating factors of safety and thus the advantages of these methods are increasingly recognized. However, the latter may suffer from numerical instabilities when using non-associated plasticity whereas the former are restricted to associated flow rules. This paper shows that these issues may be overcome by a modification of the so-called Davis approach which provides accurate estimates of the factor of safety of slopes, even for extreme cases of steep slopes with friction angles in excess of 40° and zero dilatancy.

© 2014 American Society of Civil Engineers. This paper introduces an equivalent stress for elastoplastic modeling of unsaturated soils. This equivalent stress unifies various models for unsaturated soils with regard to the stress variables used and allows for a simple separation of the saturated and unsaturated phases of behavior. Moreover, the equivalent stress computed for a given model for unsaturated soil can be used in an existing model for saturated soil so it will gain the ability to model the former. The unsaturated plastic volumetric behavior of the new model is inherited mostly from the parent model for unsaturated soil. The behavior upon shearing depends on both models: the shape of the yield locus is inherited from the original model and the increase of the elastic zone (and possible shift of the elastic zone) from unsaturation depends on the model for the unsaturated soil from which the equivalent stress was taken.

© 2015, Springer-Verlag Berlin Heidelberg. In this paper, finite element limit analysis (FELA) and semi-analytical rigid block techniques are used to investigate the influence of tunnel spacing on the undrained stability of two unlined square tunnels constructed side by side. The tunnels, which are assumed to be straight and infinitely long, are modelled under conditions of plane strain. Upper and lower bounds on the stability of the tunnels are obtained using FELA; the numerical formulation of which is based upon the bounds theorems of classical plasticity. These bounds, which bracket the true collapse load from above and below, are found to be in good agreement with one another. Rigid block methods also provided an upper bound estimate on tunnel stability which was generally higher than, but still in good agreement with, the FELA upper bound. Failure mechanisms associated with the collapse of the dual tunnels were investigated, and for deeper tunnels, it was found that mechanisms extend much deeper below the tunnels than the collapse mechanisms associated with a single tunnel. Results from this study are summarised in dimensionless stability charts for use by practitioners.

© 2014 American Society of Civil Engineers. Rock joints exert an enormous influence on the permeability of a rock mass because they act as interconnecting networks that provide pathways for fluids to permeate and flow within the rock structure. The apertures in rock joints are irregular in nature and induce flows that cannot be described by the parallel-plate theory based on planar joints or the classical cubic flow relationships. In this study, a two-dimensional (2D) hydraulic aperture distribution was considered to develop a mathematical model for fracture flow. In this approach, the three-dimensional Navier-Stokes equation was integrated over the joint aperture and converted to an equivalent 2D flow model. The proposed model was then solved numerically by adopting a well-known algorithm for coupling the pressure and velocity and implementing it in a computer program. The selected program is capable of predicting the deformation of the joint apertures on normal loading, the resulting flow patterns, and the volumetric flow rates associated with permeability tests conducted using a high-pressure triaxial apparatus that was designed and built at the University of Wollongong. The model output for different conditions of confining stresses and hydraulic gradients was computed, and a good agreement with the experimental results was observed.

© 2014 Elsevier Ltd. Experimental studies and numerical modelling of the deformation of soft clay stabilised by stone columns have been conducted over the past few decades. Continuum-based numerical models have provided valuable insight into the prediction of settlement, lateral deformation, and stress and strain-rate dependent behaviour of stone columns at a macroscopic scale, but because they consist of granular material such as crushed rock, gravel, and waste rock aggregates, their behaviour is influenced by inter-particle micromechanics and cannot be modelled properly using these models. In this paper a novel coupled model of the discrete element method (DEM) and finite difference method (FDM) is presented to study the deformation of a single stone column installed in soft ground. In this coupled discrete-continuum method, PFC2D and FLAC were used to model the interaction between the stone column and surrounding clay, respectively. The contact forces at the interface between the two zones were determined through a socket connection that allows the DEM to transfer forces and moments to the FDM and vice versa. The predicted results were comparable to the data measured experimentally, showing that the coupled discrete-continuum model proposed in this study could simulate the load-deformation behaviour of a stone column installed in clay. The contact force distribution and shear stress contour developed in the stone column and surrounding clay were captured to provide a better understanding of the load-deformation behaviour of the stone column.

© 2015 Elsevier Ltd. This paper deals with a back analysis of a slope failure. The case history investigated is located in an alpine environment in central Europe and is characterized by a very steep original terrain, indicating in situ soil with high strength. To study the factor of safety, two different approaches applying the so-called ¿'/. c' reduction are used, namely finite element limit analysis and strength reduction finite element analysis. Comparison of a strength reduction technique with rigorous finite element limit analysis confirms that the factors of safety (FoS) obtained are very similar for associated plasticity, an intrinsic assumption of limit analysis. For non-associated plasticity, a modified version of the so-called Davis approach has been applied because it has been shown that the original formulation proposed by Davis works well when the FoS is defined in terms of loads but is not appropriate when the FoS is defined in terms of soil strength. The results show that, with the modified Davis parameter, both strength reduction finite element analyses and finite element limit analyses provide very similar factors of safety. The key advantage of limit analysis, however, is that the value of the FoS can be bracketed from above and below with upper and lower bound calculations.

© 2015 Elsevier Ltd. Instability of low-lying saturated subgrade soil contributes to 'clay-pumping' that is responsible for contaminating the overlying track materials. The clay pumping occurs under the action of cyclic loading (train loading) due to the build-up of excess pore water pressure. The work contained in the paper is focused on monotonic loading response of fouled ballast and is a crucial first step towards a more complete analysis of the clay pumping effect. In this paper, a bounding surface plasticity model is presented for clay-fouled ballast within the framework of critical state soil mechanics, adopting isotropic hardening and a non-associated flow rule. The role of the constitutive parameters and their dependence on various levels of fouling is discussed. The size and shape of the bounding surface is influenced by the extent of fouling. The model is calibrated against the results of consolidated drained triaxial tests conducted using a large scale cylindrical apparatus designed and built at the University of Wollongong. The model was successfully validated against triaxial testing on fouled ballast for an array of confining pressures, and the model predictions were found to be in good agreement with the laboratory data.

© 2015 Elsevier Ltd. We present an analytical study on the vertical vibration of an elastic pile embedded in poroelastic soil. The poroelastic soil is divided into a homogeneous half-space underlying the pile base and a series of infinitesimally thin independent layers along its shaft. The dynamic interaction problem is solved by extending a method originally proposed for an embedded rigid foundation. The validity of the derived solution is verified via comparison with existing solutions. Arithmetical examples are used to demonstrate the sensitivity of the vertical pile impedance to the relative rigidity of the two soil parts.

© 2014, Springer-Verlag Berlin Heidelberg. This paper presents a numerical study of shear localization in granular materials based on a discrete element method. The plane Couette shear test is proposed for this purpose. A numerical model is established to simulate the test. With the flexible side boundaries, it is demonstrated that the plane Couette shear state can be achieved within a granular sample of limited length, and a shear band parallel to the shear direction can be obtained. Numerical results are also presented to show the formation and the development of the shear band. A homogenization procedure is employed for presenting the variation of the field variables such as stress components, the couple stress, the void ratio and the grain rotation. The evolution and the spatial distribution of these quantities are qualitatively in accordance with the Cosserat continuum model predictions. The numerical results also indicate that the Cosserat effect plays a vital role in shear localization zone.

Rainfall induced landslides vary in depth and the deeper the landslide, the greater the damage it causes. This paper investigates, quantitatively, the risk of rainfall induced landslides by assessing the consequence of each failure. The influence of the spatial variability of the saturated hydraulic conductivity and the nature of triggering mechanisms on the risk of rainfall-induced landslides (for an infinite slope) are studied. It is shown that a critical spatial correlation length exists at which the risk is a maximum and the risk is higher when the failure occurs due to a generation of positive pore water pressure. © 2014 Elsevier B.V.

In the study of landslides, it is generally assumed that an impermeable boundary exists at a certain depth and failure occurs at this boundary. In reality this is not always the case and failures can occur at any depth. This paper aims to study the effect of boundary conditions on landslides, using a series of seepage and stability analyses performed over a range of rainfall intensities, and for different failure mechanisms, by studying the failure time and depths corresponding to fully drained, partially drained, and impermeable boundaries. It is shown that these conditions can significantly affect the occurrence and depth of rainfall-induced landslides. © 2014 Elsevier Ltd.

This paper presents details of the advancements of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering to the apparatus, facilities and methods for physical modelling in geotechnics. This advancement includes (i) the launch of a National Geotechnical Centrifuge Facility with a new 10 m diameter fixed beam centrifuge that will be capable of spinning 2.4 tonnes of soil at 100 gravities, (ii) a new mobile soft soil in situ testing laboratory, (iii) a new national facility for the cyclic testing of high-speed rail and (iv) three recirculating flumes, called O-tubes, which are presented in another paper of this special issue. This paper provides an overview of this new equipment and the aims of the research that it will underpin. The equipment will provide enhanced possibilities for Australia to conduct project specific testing for future energy and transportation infrastructure developments, nationally and internationally.

The observational method is one of the most successful processes in geotechnical engineering. Performance monitoring data are the most reliable information that engineers can use to predict future performance of geotechnical projects. This paper presents two examples where Bayesian statistical methods can be used for the prediction of future performance. The first example is to update the capacity of piles using load test results. The second example is to update embankment settlement predictions when field settlement monitoring data are available.

Rail tracks undergo degradation owing to particle breakage and fouling of ballast by various fines including coal and subgrade soil. As the ballast becomes fouled, its strength and drainage capacity are compromised, sometimes resulting in differential settlement and reduced track stability. This paper demonstrates a continuum mechanics based framework to evaluate the detrimental effect of fines on the strength, deformation and degradation of coal-fouled ballast under monotonic loading. An elastoplastic constitutive model that considers the effect of fines content and energy consumption associated with particle breakage during shearing is presented. This multiphase constitutive model is developed within a critical state framework based on a kinematic-type yield locus and a modified stress-dilatancy approach. A general formulation for the rate of ballast breakage and coal particle breakage during triaxial shearing is presented and incorporated into the plastic flow rule to accurately predict the stress-strain response of coal-fouled ballast at various confining pressures. The behaviour of ballast at various levels of fouling is analysed and validated by experimental data. © 2014 Elsevier Ltd.

In this paper, numerical limit analysis and semianalytical rigid block techniques are used to investigate the effect of the tunnel spacing on the stability of two circular tunnels excavated side by side. The tunnels are modeled under plane-strain conditions, which implies that they are assumed to be infinitely long. Bounds on the stability of the tunnels are obtained using finite-element limit analysis, the numerical formulation of which is based on the upper and lower bounds theorems of classical plasticity. Solutions are obtained using advanced conic programming schemes to solve the resulting optimization problems, and upper and lower bound estimates on the stability of the tunnels are obtained for a range of geometries. These bounds, which bracket the true collapse load from above and below, are found to differ by at most 5% for the cases where the solution does not approach zero. Results from this study are summarized in stability charts for use by practitioners. © 2014 American Society of Civil Engineers.

The material point method is a novel numerical technique which is especially well-suited to solving problems involving large or extreme deformations. This paper shows the results of the modelling of flow of granular material in inclined channels. During the calculations the granular material is approximated by a Mohr-Coulomb constitutive model. The computed flow is subsequently compared to experimental results published in the literature. © (2014) Trans Tech Publications, Switzerland.

Economic growth in Australia and the rest of the world is linked to the scale of construction and mining, and the amount of earth moved each year in these operations is difficult to fathom. When distributed evenly across the world's population, each individual moves several tonnes of earth each year. This paper highlights current and future research initiatives within the ARC Centre of Excellence for Geotechnical Science and Engineering (CGSE) aimed at developing rigorous, mechanics-based models for fundamental ploughing and cutting processes in soils. State-of-the-art physical modelling is integrated with the development of new techniques for analytical and numerical modelling to elucidate and predict the full progression of forces and deformations in both two-dimensional and three-dimensional processes. A new analytical model for cutting in dry sand is presented, and preliminary results from numerical and physical modelling are described. The analyses reveal effects that available models fail to consider and illustrate how the development of rigorous models may facilitate improvements in production and efficiency in earthmoving operations.

A large-deformation numerical methodology is applied to simulate the interaction effects for a pipeline installed in a trench backfilled with loosely deposited dry sand, focusing on shallow buried pipelines subjected to lateral displacements relative to the surrounding soil. Based on the backfill-pipeline deformation mode under shallow embedment conditions, described in previous experimental studies, analyses are performed while considering only the critical state shear strength parameters of the backfill. The numerical methodology is validated against experimental full-scale test measurements from the literature, for pipelines buried in uniform dry loose and medium sand. Parametric analyses are performed to generate approximate formulas and charts for calculating (i) the maximum force on the pipeline and (ii) the minimum trench dimensions to eliminate interaction with the surrounding natural ground. Application of the proposed approach in the prediction of independent full-scale test results for a pipeline embedded in a shallow trench demonstrates its effectiveness, and underlines the effect of trench dimensioning on the response of the pipeline. © 2013 Elsevier Ltd.

The displacement finite element, lower and upper bound finite element limit analysis and analytical upper bound plasticity methods are employed to investigate the undrained limiting lateral resistance of piles in a pile row. Numerical analyses and analytical calculations are presented for various pile spacings and pile-soil adhesion factors. The numerical results are shown to be in excellent agreement with each other and also with the theoretical upper bounds produced by the analytical upper bound calculations. Based on the numerical and analytical results, an empirical equation is proposed for the calculation of the ultimate undrained lateral bearing capacity factor. This equation is subsequently used to calculate p-multipliers applicable to the lower part of piles in pile rows, which are compared to multipliers available in the literature (that are constant with depth). The comparison shows significant differences, indicating that the amount of reduction in lateral resistance due to group effects is not constant with depth as routinely assumed in practice. © 2013 Elsevier Ltd.

Free-drift batch reactor experiments using calcite (limestone, CaCO 3) were used to study fluoride removal through precipitation as fluorite (CaF2) from solutions with concentrations reflective of an industrially contaminated site. The influence of CO2 partial pressure (pCO2), stirring rate, and fluoride concentration were investigated in this paper. Equilibrium modeling shows that in wastewaters with high fluoride concentrations (~2,000 mg/L), the flux of CO2(g) to CO 2(aq) could not keep up with the consumption of CO2(aq), resulting in an initial disequilibrium with experimental pH reaching equilibrium quickly, while fluoride removal lagged. Increasing stirring rate significantly decreased the extent of disequilibrium and the time at which the CaCO 3-fluoride-CO2 system attained equilibrium due to the increased rate of transport of dissolved CO2 to the CaCO3 surface, and simultaneously the rate of transport of the dissolved CaCO 3 to the bulk solution. Optimal fluoride removal occurs at pCO 2~10-0.52 [30% (mol% CO2)] with 96% of the initial 2,000 mg/L fluoride load removed in less than 80 min with a stirring rate of 300 revolutions per minute. Increasing pCO2 to ~100 (100% CO 2) resulted in very little gain, less than 2%, in fluoride removal, or in the time required to reach equilibrium and therefore significant remediation cost savings can be obtained by using pCO2 30% when compared to 100%. © 2013 American Society of Civil Engineers.

Based on a micropolar (Cosserat) continuum model, the formation of shear localization in granular materials is studied analytically and numerically. The possibility of shear localization in a uniformly deforming granular body is studied as a bifurcation problem. The analysis shows that shear bifurcation on the constitutive model level is suppressed in a micropolar continuum approach. Numerical studies are presented to show that the development of shear localization is a result of initial imperfection which exists inevitably in granular bodies. © Institute of Materials Engineering Australasia Ltd 2005.

In this paper, fundamental mathematical concepts for modeling the dissipative behavior of geomaterials are recalled. These concepts are illustrated on two basic models and applied to derive a new form of the evolution law of the modified Cam-clay model. The aim is to discuss the mathematical structure of the constitutive relationships and its consequences on the structural level. It is recalled that non-differentiable potentials provide an appropriate means of modeling rate-independent behavior. The Cam-clay model is revisited and a standard version is presented. It is seen that this standard version is non-dissipative, which at the same time explains why a non-standard version is needed. The partial normality is exploited and an implicit variational formulation of the modified Cam-clay model is derived. As a result, the solution of boundary-value problems can be replaced by seeking stationary points of a functional. © 2005 Springer.

In this paper, shear localization in granular materials is studied as a bifurcation problem based on a conventional (non-polar) and a micro-polar continuum description. General bifurcation conditions are formulated for a non-polar hypoplastic model and its micro-polar continuum extension. These conditions de.ne stress, couple stress and density states at which weak discontinuity bifurcation may occur. The stress states for bifurcation are then compared with the peak stress states, which define a bounding surface for the accessible stress domain in the principal stress space. The results show that, in a micro-polar continuum description, the constitutive model may no longer be associated with weak discontinuity bifurcation. © 2005 Springer.

This paper investigates the performance of various load-stepping schemes for finite element analysis with critical state soil models. The accuracy of simple incremental schemes is found to be strongly influenced by the load increment size, the type of flow rule, and the overconsolidation ratio. Similarly, these factors are shown to have a pronounced effect on the efficiency and stability of some classical iterative schemes. Unless they are performed with small load steps, critical state analyses with fixed increment sizes frequently exhibit non-convergent behaviour or lead to inaccurate solutions. The automatic incrementation schemes developed by Abbo and Sloan (International Journal for Numerical Methods in Engineering 1996; 39: 1737-1759; Proceedings of 5th International Conference, Owen DRJ, Onate E, Hinton E. International Center for Numerical Methods in Engineering, Barcelona, 1997; 1:325-333), which are based on standard methods for integrating systems of ordinary differential equations, are shown to be efficient, accurate and robust solution techniques for a wide variety of critical state problems. © 2001 John Wiley & Sons, Ltd.

Discontinuity Layout Optimization (DLO) (Smith & Gilbert 2007) is an upper bound limit analysis technique for modeling the stability of geotechnical problems. Meshes used for DLO are typically generated by interconnecting a set of nodes (n) located at regular grid points within a domain. A regular grid allows the required mesh topology to be generated in approximately O(n2) time by searching for pairs of integer coordinates with unity as their greatest common divisor. This technique avoids impractical O(n3) worst case mesh generation times, but produces a non-optimal discretization. Using the concept of point-line duality, a procedure for assembling meshes on a non-uniform cloud of nodes in O(n2) time is proposed. The flexibility afforded by this newmethod is used to adaptively refine a DLO mesh by adding nodes in regions with the greatest estimated error. The effectiveness of this procedure is demonstrated by analyzing the stability of a strip footing on a Mohr-Coulomb soil. © 2015 Taylor & Francis Group, London.

Finite element limit analysis and rigid block upper bound methods are used to investigate the undrained stability of tall rectangular and horseshoe shaped tunnels.A parametric study, that considered a range of soil properties and tunnel geometries, was performed to study the stability of tunnels which are taller than they are wide. Rigorous upper and lower solutions for the tunnel stability, which bracket the true solution, are found using Finite Element Limit Analysis. This finite element technique implements a discrete form of the bound theorems of classical plasticity by employing adaptive meshing and a bespoke conic programming scheme to solve the resulting optimisation problem. The computed bounds on stability generally bracket the true collapse load to within 2% and are presented as a series of stability charts suitable for practical use. © 2015 Taylor & Francis Group, London.

Rainfall induced landslides can vary in depth and deeper the landslide, greater is the damage it causes. This paper investigates, quantitatively, the risk of rainfall induced landslides by assessing the consequence of each failure. The influence of the spatial variability of the saturated hydraulic conductivity on the risk of landslides is studied. It is shown that a critical spatial correlation length exists at which the risk is a maximum. © 2015 Taylor & Francis Group, London.

The paper presents a number of numerical simulations of triaxial shear tests. The simulations have been made with the Generalised Interpolation Material Point method (GIMP, Bardenhagen & Kober 2004), which allows for modelling of large displacements, such as those occurring in shear bands. The simulations are assessed qualitatively and compared with available numerical results. Unconstrained compression tests on unsaturated soil specimens are also simulated. In all the analyses, the Mohr-Coulomb model, extended into the unsaturated regime, was used. The paper is part of a joint research program in the Centre for Geotechnical Science and Engineering which aims to assess and to validate the material point method for engineering purposes. © 2015 Taylor & Francis Group, London.

This study outlines the development of a computational scheme which accounts for large deformation dynamic behaviour of saturated porous media and models soil-structure interaction using a high-order frictional contact algorithm. The numerical scheme is employed to analyse a dynamic coupled problem of pipeline-seabed interaction in two steps, including the simulation of the dynamic embedment process as well as the subsequent consolidation stage. The analysis considers a frictional interface between the pipe and the soil which is normally ignored in most analyses due to numerical difficulties. The nonlinear behaviour of the solid constituent is captured by the Modified Cam Clay soil model, allowing the incorporation of shear-induced pore water pressures during the embedment process. The results of this study indicate that the proposed method is able to solve the highly nonlinear problem of dynamic soil-pipe interaction coupled with pore water pressures and Darcy velocity. The results also show that a dynamic approach is necessary for coupled problems of pipe-seabed interaction involving very fast loading. © 2015 Taylor & Francis Group, London.

This work consists of a preliminary numerical study on the impact behaviour of rock blocks on muckpiles using the Discrete Element Method (DEM). A contact law using a linear hysteresis model for normal contacts and a Mohr-Coulomb model for tangential contacts is used. In addition, two dissipative laws are introduced consisting of a moment transfer law and normal viscous damping law. One of the aims of this study is to investigate if the contact law enables a realistic modelling of the rebound characteristics of a block during impact on a muckpile. A parametric study is carried out in order to investigate the influence of the constitutive model parameters and the presence of clumps. Numerical predictions are compared to experimental results. It is shown that clumps in the muckpile are essential to reproduce realistic results. © 2015 Taylor & Francis Group, London.

Copyright © 2015 by the International Society of Offshore and Polar Engineers (ISOPE). The dynamic penetration of anchors into the seabed is an important problem in offshore geomechanics and one of the most challenging for geotechnical analysts. Complications due to the nonlinear material response of the soil, the large deformations caused by the insertion of the object, and the changing boundary conditions at the contact between the soil and the anchors must be taken into account. Moreover, the presence of a pore fluid, and the pressure that it may exert, requires a fully coupled displacement-pore pressure analysis. Recent work has facilitated the modelling of the dynamic penetration of objects into soil. The finite element method is one of the most commonly used techniques for tackling problems of soil penetration because the resulting solutions satisfy the equation of dynamic equilibrium and the method can incorporate sophisticated soil models as well as complex boundary conditions. This study discusses a number of challenging aspects of the numerical simulation of dynamically embedded anchors, particularly torpedo anchors, and presents a robust analysis strategy for such problems. This technique is based on the Arbitrary Lagrangian-Eulerian method and rigorously incorporates displacements, velocities, and accelerations of the solid phase along with the pore pressure and velocities of the fluid phase.

The mechanical properties of natural materials such as rocks and soils vary spatially. This randomness is usually modelled by random field theory so that the material properties can be specified at each point in space. When these point-wise material properties are mapped onto a finite element mesh, discretization errors are inevitable. In this study, the discretization errors are studied and suggestions for element sizes in relation with spatial correlation lengths are given. © (2014) Trans Tech Publications, Switzerland.

Some common criteria for predicting the plastic failure of geomaterials, including the Mohr-Coulomb model, can be represented as conic constraints. Thus, by formulating finite element limit analysis (FELA) problems with such materials as second-order cone programs (SOCPs), solutions to small- and medium-scale problems are readily obtained using current state-of-the-art optimisation software that are based on polynomially-bounded interior-point methods (IPMs). Unfortunately, when progressing to large-scale 2D and 3D problems, these schemes often struggle with the increased computational burden of obtaining a search direction at each iteration of the IPM using conventional direct solvers that implement some form of Gaussian elimination. In this paper, current conic optimisation software is compared for some medium and large-sized FELA problems. Additionally, a scheme which avoids the factorisation of large linear systems, through the use of a Krylov subspace solver, is developed and compared to existing software. © (2014) Trans Tech Publications, Switzerland.

Analytical probabilistic analysis and Monte Carlo simulation based on elasto-plastic Finite Element Method (FEM) on dry soil mix columns are presented. It is shown that analytical method is over conservative because it ignores the supports from adjacent columns. Probabilistic FEM analysis can provide more accurate predictions, and thus lead to more economic designs. Probabilistic FEM analyses show that the effects of adjacent columns can be destructive when applied load is close to the strength. The reliability of the system of columns is analyzed by setting residual strength to zero. Results show that close spacing has more safety margin than loose spacing. © 2014 Taylor & Francis Group, London.

This paper presents a discrete modelling approach which allows the simulation of rockfalls behind drapery systems. The falling rock is represented by a rigid assembly of spheres whereas the slope is represented by triangular elements. Energy dissipation during impact on the slope is considered via friction and viscous damping. The drapery is represented by a set of spherical particles which interact remotely. The numerical model is used to investigate the efficiency of a drapery system. Various simulations with two different block sizes are performed and the numerical predictions of simulations with drapery are compared to simulations without drapery in order to assess the performance of the protection system.