Bounding Surface Plasticity Model Research Articles

Seismic analysis of landfill using advanced numerical approach considering material and contact nonlinearity

Seismic stability is of vital importance for municipal solid waste (MSW) landfills and this study proposes an advanced numerical approach considering material and contact nonlinearity for seismic analysis of landfill. The MSW is modeled as porous media through the u-p formulation and the bounding surface plasticity model based on the double-phase assumption is adopted. The dynamic friction model is applied to define the interface shear behavior so that the elastoplasticity and displacement-softening property of the liner interface can be well reflected. The advanced numerical method is validated through back analyses of soil column tests and centrifuge tests of landfills. The subsequent site-specific case study indicate that earthquake-induced sliding along the liner system is a typical failure mode of canyon landfill and the stability can be assessed based on the permanent displacement, which can also be roughly estimated with simplified semiempirical models by setting the yield coefficient as the residual friction coefficient of the liner interface.

Verification of bounding surface plasticity model with reversal surfaces for the analysis of liquefaction problems

This paper presents the verification of a new bounding surface plasticity model with reversal surfaces when used in boundary value problems related to liquefaction. The model is implemented in a commercial finite-difference code using an explicit stress integration algorithm. After validating the model against element tests on Nevada sand, the paper employs the same set of values of model parameters for ascertaining the model's simulative potential at the system level, via comparisons with data from 8 dynamic centrifuge tests performed on the same sand. These pertain to: a) the free-field response of a horizontal liquefiable layer, b) the lateral spreading response of a gently sloping liquefiable layer and c) the seismic response of rigid foundations on a single-layered and two-layered horizontal liquefiable ground profiles. Parametric analyses emphasize the effects of non-constant sand permeability coefficient and excitation intensity on the liquefied system response. Similar analyses highlight the importance of post-liquefaction strain accumulation and the avoidance of stress-strain overshooting, both constitutive attributes of the new model.

Development of an advanced constitutive model for spoil-structure interaction problems

Revitalisation options for mine spoil heaps is an important issue to consider when planning for post-mining land use. One option is the installation of wind turbines on the spoil heaps, which provide a sustainable energy source. This option poses challenges for foundation design due to the nature of the spoil material, which is usually highly heterogeneous due to the way spoils are deposited, and can contain high proportions of high-plasticity cohesive soils (clay). This paper presents results obtained using an advanced constitutive model that was developed to simulate cohesive mine spoil behaviour and presents model results for the prediction of foundation response under both monotonic and cyclic loading. The model is a modified version of the original isotropic bounding surface plasticity model that additionally involves a damaged-based plastic modulus in order to realistically represent soil strength degradation induced by cyclic action. The model is used for the simulation of shallow foundations for onshore wind turbines on a cohesive clay with a heterogeneous (linearly increasing) undrained shear strength (random spatial variability is not considered). Two different loading scenarios of a shallow strip foundation are considered in the paper: a pure moment-vertical loading (M-V), and a moment-horizontal-vertical loading (M-H-V). The effect of the adopted spoil-foundation interface type is also considered: (1) a fully-bonded interface and (2) a tensionless interface. Results demonstrate that, though the vertical bearing capacity is only slightly affected by the interface properties, the moment capacity is shown to be strongly influenced by the predefined contact conditions. For the footing system under M-H-V loading, a dominant footing uplift mechanism is obtained for light structures and the opposite holds for heavily loaded structures, where significant settlement accumulation occurs during cyclic loading. Based on the analysis, the moment bearing capacity of the footing system decreases as the slenderness ratio and/or the vertical safety factor increase, and the opposite mechanism is obtained as the strength heterogeneity degree increases.

Cyclic compression of sands at constant stress ratio—experimental investigations and constitutive modelling

Several constitutive models for sands are based on an additive split of the effective stress rate into two terms. One term accounts for the deviatoric stress ratio varvec{r}, the other for the mean effective stress {p}. While sophisticated techniques are available to account for monotonic and cyclic variations of varvec{r}, the {p} term is usually treated by means of rather rudimentary constitutive mechanisms. In particular, no plasticity sand model seems to exist whose functions take into account cyclic changes of {p} in a realistic manner. However, cyclic changes of {p} frequently occur in geotechnical boundary value problems and can cause irrecoverable deformation in non-cohesive soils. Present sand models significantly under- or overestimate these deformations. This issue is tackled in the paper. First, results from a comprehensive series of triaxial tests on Toyoura Sand are presented. The samples were loaded with cyclic changes of {p} at constant stress ratio in order to study the effects of mean effective stress variations exclusively. The test results show that the samples accumulate significant irrecoverable strains throughout successive loading cycles. The results furthermore allow to investigate the effects of pressure level, pressure amplitude, stress ratio level and density on the strain evolution. Second, new constitutive functions for an existing Bounding Surface Plasticity model are proposed in the paper. They are intended to improve the simulation results obtained with the model for monotonic and cyclic changes of {p} at constant stress ratio. The extended model is then carefully calibrated and validated using the experimental data from the triaxial tests. The results of the validation prove that the new constitutive functions have the desired effect.

Application of an Optimization Algorithm for Calibrating Soil Bounding Surface Plasticity Models for Cyclic Loading

Application of an Optimization Algorithm for Calibrating Soil Bounding Surface Plasticity Models for Cyclic Loading

Bounding surface plasticity model with reversal surfaces for the monotonic and cyclic shearing of sands

Bounding surface plasticity model with reversal surfaces for the monotonic and cyclic shearing of sands

Enhanced anisotropic bounding surface plasticity model considering modified spacing ratio of anisotropically consolidated clay

Enhanced anisotropic bounding surface plasticity model considering modified spacing ratio of anisotropically consolidated clay

A bounding surface plasticity model for expanded polystyrene-sand mixture

This study presents a bounding surface plasticity model to capture the stress-strain responses of expanded polystyrene (EPS)-sand mixture with various EPS content levels. Based on the mechanical responses in isotropic and triaxial tests, a generalized void ratio concept is applied to the potential deformation characteristics of EPS beads. Subsequently, the void ratio-isotropic stress curve can be expressed in a semi-log space, which shows a three-linear-segments manner corresponding to three typical mechanisms (elastic compression, normal compression and sand particle embedding in EPS beads). The plasticity model is formulated within the framework of critical state concept. For the sake of simplicity, the raindrop shaped yield function has been applied to describe the bounding surface, with a non-associate flow rule being adopted to capture the plastic deformation. Thus, this model requires fewer model parameters, most of which can be calibrated through conventional isotropic and triaxial test. By considering the weakening effect caused by including EPS, special treatment has been applied to EPS proportion dependent parameters. The capability of the proposed model has been demonstrated through a model simulation on EPS-sand mixtures with different EPS proportions and various confining pressures.

Fractional-order bounding surface model for unsaturated soils under cyclic loading

Modelling of unsaturated soil stress–strain relationships under cyclic loading with constant matric suction is a topic that is poorly addressed by the current literature. Using the theoretical framework of the bounding surface plasticity and Barcelona basic model (BBM) combined with the concept of fractional accumulated strain rate, a bounding surface model for accurately describing the unsaturated soil stress–strain relationship with constant matric suction is established here. The fractional accumulated strain rate is introduced to consider the influence of cyclic loading history. The movable mapping centre rule is used to describe the hysteresis characteristics of the dynamic stress–strain curve during the unloading process. The shape of the dynamic stress–strain curve can be described reasonably by considering the cyclic loading process as the three processes of initial loading, unloading, and reloading. The cyclic loading test data of unsaturated silt, sand, and lean clay with constant matric suction is used for parameter calibration and model validations. Results show that the proposed model can accurately capture the dynamic stress–strain relationship of unsaturated soil with constant matric suction.

A bounding surface plasticity model for cemented sand under monotonic and cyclic loading

A plasticity model is proposed to simulate the monotonic and cyclic behaviour of cemented sand. The model is an extension of the critical state-based bounding surface plasticity model originally developed for clean sand by researchers Y. F. Dafalias and M. T. Manzari in 2004. The elastic parameters, state parameter, yield function, flow rule and plastic modulus of the base model are modified for cemented sand mainly by incorporating a bonding strength variable. In addition, the critical state variables, stress ratio and void ratio of cemented sand are linked to the initial cement content. The model formulation is presented first in the triaxial and then in generalised stress space. The capabilities of the model are illustrated by simulating the response in a series of monotonic and cyclic tests on cemented sand. This shows that the model can capture the main features of the mechanical behaviour of cemented sand well, including cement-induced enhancements of stiffness, strength, dilatancy and liquefaction resistance.

Inclined loading of horizontal plate anchors in sand

The performance of plate anchors in sand, relative to clay, is not well understood, particularly for the more realistic case of an inclined load. This paper investigates the effect of load inclination on horizontal plate anchors in sand through centrifuge tests and numerical finite-element simulations. The centrifuge tests were performed on rectangular plate anchors in loose and dense sand, at shallow embedment depths with four different load inclinations. The experiments showed that the anchor capacity of horizontal plates increased progressively as the load inclination became progressively more horizontal, with anchor capacity under pure horizontal loading being approximately 1·8 times higher than that under pure vertical loading. These experimental observations were also replicated in finite-element simulations using a bounding surface plasticity model. Investigation of the underlying failure mechanisms and stress paths showed that the slip planes become longer and the mobilised lateral stresses increase as the load inclination becomes increasingly horizontal, which leads to higher anchor capacities. Finally, the anchor resistance factors from the numerical analyses were decoupled into vertical and horizontal components and represented as interaction diagrams, providing a basis for performing hand calculations of anchor capacity for a given embedment depth, load inclination and relative density.

A bounding surface plasticity model for unsaturated structured soils

A bounding surface plasticity model based on the effective stress concept is presented to describe the behaviour of unsaturated structured soils subjected to hydro-mechanical loadings. The structural degradation effects on the compressive and tensile strength are considered through controlling the size of the bounding surface, allowing for a smooth transition of the response from structured to unstructured states. The structural degradation is modelled using a work hardening approach, considering both the effects of stress magnitude and accumulated plastic strain on the degradation process. A void ratio-dependent water retention model is adopted, taking the effect of hydraulic hysteresis into account. Attention is also given to the stiffening effect of a decrease in the degree of saturation on the mechanical response of unsaturated structured soils and the wetting-induced collapse. A radial mapping rule with a mobile centre of homology is adopted to capture the response of the soil under unloading–reloading conditions. The predictive capability of the model is demonstrated through the comparison of the model simulations with experimental data for different conventional laboratory tests including constant-suction oedometer and triaxial shearing and wetting tests.

Dynamic behaviour of a piled raft resting on saturated Kasai River sand

ABSTRACT The present work intends to calibrate the cyclic triaxial test and validate the 1-g shake table test of piled raft on saturated Kasai River sand. The outcome of the cyclic tests on Kasai river sand is already reported in the literature, but the present paper attempts to identify and explain the failure modes of the cyclic triaxial test as well as to numerically calibrate the experimental data(s) for relative density of 40% and 60%. For numerical validation and calibration, a bounding surface plasticity model is used. The calibrated parameters obtained from the element tests are used for validation of 1-g shake table test of piled raft resting on saturated sand. The numerical predictions are in good agreement with the experimental observations (in terms of acceleration, pore pressure). In addition, the effect of superstructure loading on piled raft is investigated in terms of variation of pore pressure (or effective stress) near and away from the structure and mechanism for vertical settlement of piled raft is identified. The relevant parameters related to seismic design of piled raft are identified and design guidelines in terms of strength and serviceability has been proposed.

Generalized Mapping Rule for Image Point Identification in 3D Bounding Surface Plasticity Models

Abstract This paper presents a generalized yet simple mapping rule for image point identification in 3D bounding surface plasticity (BSP) models. It is based on the determination of the correct loc...

Efficient analysis of cyclic laterally loaded piles

The analysis and design of piles subjected to lateral cyclic loads that induce significant plastic responses requires numerical models for the lateral soil resistance capable of representing the fundamental soil responses observed in such conditions. A bounding surface plasticity model with traditional p-y concepts has been implemented in a finite element model and successfully benchmarked against physical tests revealing significant cyclic responses in both one- and two-way loading conditions. The model includes two kinematic hardening surfaces and a fixed limit surface beyond which the kinematic surfaces cannot pass. The benchmarking effort resulted in standardized values for several model parameters for p-y applications. The remaining model parameters are easily calibrated against the expected p-y response under monotonic loading conditions for fine grained soils. The analysis method is extremely efficient, requiring the same level of effort as that typical of traditional p-y techniques. The results presented demonstrate that the model accurately reproduces observed pile cyclic hysteresis, plastic energy dissipation, and stiffness degradation, all of which are neglected in traditional elasticity-based p-y models. It has distinct advantages for static and dynamic analyses involving complex loading histories involving significant plastic soil response and is suitable for site specific analyses. This study is confined to planar conditions, but similar models have been implemented for arbitrary loading directions.

On the implementation and validation of a three‐dimensional pressure‐dependent bounding surface plasticity model for soil nonlinear wave propagation and soil‐structure interaction analyses

AbstractNumerous experiments and prior analyses have confirmed that soil inelasticity, which is known to come into effect even at very low strain levels, can significantly affect site response and dynamic soil‐structure interaction (SSI) behavior. To date, only a few studies were able to consider multi‐axial wave propagation problems with appropriate models of soil nonlinearity. Most existing works are limited to either homogeneous soil configurations or equivalent linear soil models. The instances wherein soil nonlinearity is accurately considered have been confined to single element tests and one‐dimensional problems. In this study, an improved pressure‐dependent bounding surface plasticity soil model—with appropriate plastic strain rate direction definition and overshooting correction scheme—is implemented in Abaqus, and validated using recordings from both the Lotung borehole array and centrifuge test data on embedded flexible structures. The implemented model is capable of comprehensively reproducing complex soil behaviors, such as stiffness degradation, damping, dilatancy, and compaction while under a wide strain range, and under general loading conditions using only a few material parameters to be calibrated. Consequently, numerically predicted results are observed to be in better agreement with experimentally measured data, in comparison with linear and another plasticity model, which include accelerations, and bending and hoop strains along the walls of the specimen structures, for low‐ as well as high‐amplitude input motions.

Bounding-Surface Plasticity Model for Drained Cyclic Behaviors of Cohesionless Soil

Abstract To describe the drained behaviors of cohesionless soil through a concise constitutive approach, a single-surface model is constructed on the concept of the bounding surface. Based on obser...

Numerical Analysis of Shallow Foundations Resting on Granular Columns Embedded in Liquefiable Soil

Shallow footings are the most preferred foundations for buildings due to low cost and ease of construction. However, under seismic loads, these foundations may suffer excessive settlements, particularly when there is a risk of soil liquefaction. This paper explores the effectiveness of granular columns in mitigating the liquefaction-induced ground deformations under shallow foundations, using FLAC2D program. PM4Sand, a critical state-based bounding surface plasticity model is used to simulate the stress–strain response of sand to cyclic loading. The responses of granular columns are also simulated using the same soil model. Validation of the numerical model is presented against the experimental results of mildly sloping ground. The application of granular column groups resulted in maximum reduction of the settlement of footing by 60% when soil densification is included along with drainage and stress redistribution effects. Though excess pore water pressure is relatively low in treated deposit compared to the untreated deposit, its contribution to the reduction in settlement of footing is found to be minimal.

SANISAND-MSf: a sand plasticity model with memory surface and semifluidised state

A new constitutive model for sand is formulated by incorporating two new constitutive ingredients into the platform of a reference critical state compatible bounding surface plasticity model with kinematic hardening, in order to address primarily the undrained cyclic response. The first ingredient is a memory surface for more precisely controlling stiffness affecting the plastic deviatoric and volumetric strains and ensuing excess pore pressure development in the pre-liquefaction stage. The second ingredient is the concept of a semifluidised state and the related formulation of stiffness and dilatancy degradation, aiming at modelling large shear strain development in the post-liquefaction stage. In parallel, a modified flow rule aimed at providing a better description of non-proportional monotonic and cyclic loading is introduced. With a single set of constants, for which a detailed calibration procedure is provided, this new model successfully simulates undrained cyclic torsional and triaxial tests with different cyclic stress ratios, separately for the pre- and post-liquefaction stages, as well as liquefaction strength curves based on [Formula: see text] and shear strain criteria for initial liquefaction. The successful reproduction of the sand element response under undrained cyclic shearing contributes to future applications in realistic and thorough seismic site response analysis.

Finite-element modelling of laterally loaded piles in a dense marine sand at Dunkirk

The paper presents the development of a three-dimensional finite-element model for pile tests in dense Dunkirk sand, conducted as part of the PISA project. The project was aimed at developing improved design methods for laterally loaded piles, as used in offshore wind turbine foundations. The importance of the consistent and integrated interpretation of the soil data from laboratory and field investigations is particularly emphasised. The chosen constitutive model for sand is an enhanced version of the state parameter-based bounding surface plasticity model, which, crucially, is able to reproduce the dependency of sand behaviour on void ratio and stress level. The predictions from three-dimensional finite-element analyses, performed before the field tests, show good agreement with the measured behaviour, proving the adequacy of the developed numerical model and the calibration process for the constitutive model. This numerical model directly facilitated the development of new soil reaction curves for use in Winkler-type design models for laterally loaded piles in natural marine sands.