Constitutive Model For Sand Research Articles

Performance of an advanced sand constitutive model in modelling soil and soil-structure interaction under seismic excitation

There is a growing number of available advanced soil constitutive models aimed at capturing soil cyclic behaviour and their subsequent use in seismic applications. Nevertheless, detailed validation studies of these soil constitutive models on benchmark experimental works including seismic soil-structure interaction are still rare. This work presents a short validation study of the seismic performance of an advanced elastoplastic sand constitutive model on a boundary value problem including kinematic and inertial soil-structure interaction. The results of the finite element numerical model for the free field and structural responses are compared with the experimental work on a group of piles analysed in a flexible soil container filled with dry sand and subjected to simplified seismic loading. In general, the comparisons show a satisfactory match between the results of the simulations and the experiments, with the exception of the numerical predictions of settlements. The computed results are discussed based on: i) the dominant stress-paths in soil; ii) parametric studies on the settlement evaluation; iii) the origin of the high frequency motion oscillations to simple sinusoidal input motions; all with respect to potential improvements in the formulation of the elastic behaviour of the constitutive model in the future.

Spatial variability of shear wave velocity: implications for the liquefaction response of a case study from the 2010 Maule Mw 8.8 Earthquake, Chile

Assessing the potential and extent of earthquake-induced liquefaction is paramount for seismic hazard assessment, for the large ground deformations it causes can result in severe damage to infrastructure and pose a threat to human lives, as evidenced by many contemporary and historical case studies in various tectonic settings. In that regard, numerical modeling of case studies, using state-of-the-art soil constitutive models and numerical frameworks, has proven to be a tailored methodology for liquefaction assessment. Indeed, these simulations allow for the dynamic response of liquefiable soils in terms of effective stresses, large strains, and ground displacements to be captured in a consistent manner with experimental and in-situ observations. Additionally, the impact of soil properties spatial variability in liquefaction response can be assessed, because the system response to waves propagating are naturally incorporated within the model. Considering that, we highlight that the effect of shear-wave velocity Vs spatial variability has not been thoroughly assessed. In a case study in Metropolitan Concepción, Chile, our research addresses the influence of Vs spatial variability on the dynamic response to liquefaction. At the study site, the 2010 Maule Mw 8.8 megathrust Earthquake triggered liquefaction-induced damage in the form of ground cracking, soil ejecta, and building settlements. Using simulated 2D Vs profiles generated from real 1D profiles retrieved with ambient noise methods, along with a PressureDependentMultiYield03 sand constitutive model, we studied the effect of Vs spatial variability on pore pressure generation, vertical settlements, and shear and volumetric strains by performing effective stress site response analyses. Our findings indicate that increased Vs variability reduces the median settlements and strains for soil units that exhibit liquefaction-like responses. On the other hand, no significant changes in the dynamic response are observed in soil units that exhibit non-liquefaction behavior, implying that the triggering of liquefaction is not influenced by spatial variability in Vs. We infer that when liquefaction-like behavior is triggered, an increase of the damping at the shallowest part of the soil domain might be the explanation for the decrease in the amplitude of the strains and settlements as the degree of Vs variability increases.

Neohypoplasticity Revisited

AbstractThis paper presents further improvements to the neohypoplasticity (NHP), a constitutive model for sand, which overcomes some shortcomings of widely used hypoplastic models. The novelties presented in this paper includes a new description of the additional dilatancy due to the structural variable and the introduction of a new state variable, denoted as , to consider the small strain stiffness in case of a 1D loading reversal. They remove shortcomings of earlier versions of NHP. The new formulations are presented and the performance of NHP is validated with experimental data from Karlsruhe fine sand. Both monotonic and cyclic tests are simulated under drained and undrained conditions. The results demonstrate that the NHP accurately reproduces the observed behaviour in monotonic and cyclic experiments.

Nonlinear Soil Behavior Model in Localized Lagrange Multipliers Mixed Formulation (u,p) for Dynamical Analysis of Wind Turbine Coupled Systems

Coupled mechanical systems can be complex, especially if there are many systems connected together and nonlinearities are present. Soil-structure interaction refers to the interaction between a structure and the soil or foundation upon which it is built. This interaction is important because it can affect the behavior of the structure, particularly during earthquakes or other dynamic events. For the wind turbine foundation design, the soil should support the weight of a wind turbine and anchor it to the ground. This paper presents a nonlinear material behavior soil coupled to elastic structure in offshore conditions. The goal of this work is to develop a coupled structural finite element procedure using Localized Lagrange Multipliers (LLM) at idealized offshore wind turbines with nonlinear poroelastic model for soil foundation. In this work, an anisotropic sand constitutive model is used to describe the soil foundation behavior. This model is based in a critical state soil mechanics and bounding surface plasticity. Classical elasto-plasticity theory is used to obtain the soil stiffness. The numerical model is validated through a fully coupled model at classical problems results. The mixed formulation [Formula: see text] is used to model the interface frames between the domains. The momentum equilibrium and mass continuity equations are solved by algebraic equation system imposed by Lagrange multipliers methodology. In order to excite the system, aerodynamic forces are imposed in random wind velocity conditions. In another numerical case, the response of coupled system during shaking is simulated by a horizontal input motion at bottom of soil foundation. Some computational aspects are discussed and the numerical model is clarified. The classical Newton Method to solve nonlinear problems is used in a finite element approach. In addition, two foundation models are tested and time dynamic responses are evaluated for a range of physical parameters including the wind nature and soil properties.

Numerical simulation of cyclic shear tests considering the fabric change and principal stress rotation effects

AbstractCyclic loadings could induce complicated soil responses, including the fabric change and principal stress rotation, both of which would reduce the effective confining pressure and accelerate the build‐up of excess pore water pressures, thus leading to sand liquefaction in undrained conditions. The principal stress rotation, even without the change of principal stress magnitudes, would further generate the accumulative plastic shear strains. However, most of the existing studies focus on their individual effect and the combined effect was seldom considered. In this paper, a numerical approach including an elastoplastic sand constitutive model is proposed to consider the combined effect of the fabric change and principal stress rotation. In this model, the fabric change is considered with the anisotropic critical state theory and the principal stress rotation is considered by splitting the plastic strain increment into the monotonic part and rotational part. By simulating a series of cyclic shear tests, results from the numerical solutions are found showing good agreements with the existing experimental results and the importance of considering the combined effect is demonstrated. The approach can be used to predict the stress‐strain response of sand and guide the design of foundations especially in undrained cyclic loading conditions, for example, earthquake loadings conditions.

Lateral load response of large-diameter monopiles in sand

Due to the increasing demand for renewable clean energy, there has been rapid growth in the development of offshore wind energy resources in recent years. The majority of offshore wind turbines are founded on single, large-diameter, open-ended pipe piles known as monopiles. The design of these piles is often done using the p–y method, which models the soil simply as non-linear springs placed along the pile length and assumes the pile to behave as a one-dimensional beam. To develop a design method that accounts for three-dimensional pile–soil interaction and that is applicable to general conditions, a series of finite-element (FE) analyses covering a wide range of pile dimensions, wall thicknesses, slenderness ratios, load eccentricities, sand types and sand relative densities were performed using an advanced sand constitutive model. In this paper, a set of equations is proposed that can be used to estimate the critical pile length, Lcrit (the pile length beyond which the pile lateral capacity no longer increases), the lateral capacity, H, and the lateral load–rotation curve for monopiles. The proposed method produces estimates of the lateral capacity of monopiles that are in very close agreement with those from the FE analyses.

A basic constitutive model for sands

A basic constitutive model for sands

Multi-fidelity approach for uncertainty quantification of buried pipeline response undergoing fault rupture displacements in sand

A new efficient approach for uncertainty quantification of pipeline structural response undergoing reverse-slip fault rupture displacements in sand is presented using multi-fidelity Gaussian processes. Uncertainty quantification problems generally take large numbers of scenarios to be analysed considering variations in the influencing parameters. Analysing large numbers of computationally expensive detailed geo-technical numerical models is practically not feasible. Hence, a multi-fidelity approach employing Gaussian process is proposed to tackle this problem which combines the accuracy of a relatively few number of detailed geo-technical numerical models and the efficiency of large numbers of simplified numerical models to track the uncertainty response. The detailed model utilizes a previously validated pipe-soil finite element (FE) model including a non-linear sand constitutive model implemented in finite element software ABAQUS. The simplified model utilizes beam element pipe and bi-linear soil springs. The multi-fidelity model is first trained using data from high-fidelity and low-fidelity model analyses, thereafter cross-validated and subsequently used to quantify uncertainty in the peak compressive strains generated and to identify the most sensitive input variables. Finally, fragility curves are derived for a site specific pipe-soil fault rupture problem.

Cyclic lateral response of OWT bucket foundations in sand: 3D coupled effective stress analysis with Ta-Ger model

Bucket foundations have been increasingly used to support offshore wind turbines as alternatives to monopiles. Despite the substantial research effort on the bearing capacity and stiffness of such foundations in recent year, there is still a lack of knowledge regarding their cyclic response in saturated sand. In this paper, the multiaxial sand constitutive model Ta-Ger implemented in the finite deference code FLAC3D is employed in the analysis of the lateral response of bucket (skirted) foundations subjected to wind/wave loading. The model is reformulated to reproduce the cyclic response of sand for undrained, fully drained and partially drained conditions, using a unique set of calibration parameters. Having been calibrated against laboratory data available in literature, it is then used to predict the long-term cyclic lateral response of a bucket foundation in dry medium dense sand from a centrifuge experiment. After building confidence in the numerical approach the drainage effects are investigated. To gain qualitative insights into the effect of drainage conditions, the 3D numerical model, used to simulate the centrifuge test, was analyzed under saturated conditions and a range of soil permeabilities. It was shown that when flow is allowed the response up to a number-of-cycles threshold resembles that of fully drained conditions. Above this threshold, significant and abrupt increase of excess pore water pressures occurs causing liquefaction. Increasing the permeability delays the occurrence of liquefaction and the associated development of large deformations

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.

Calibration of a Hypoplastic Constitutive Model with Elastic Strain Range for Firoozkuh Sand

A series of laboratory experiments on Firoozkuh sand were conducted followed by a set of numerical simulations to determine the parameters of a general hypoplastic constitutive model for sand. This model describes inelastic and incrementally nonlinear material properties without a yield surface and detached strain increments in the elastic and plastic portions that is used to accurately simulate soil behavior for small and large strains and unloading–reloading paths. The general models are salient and the model requires unique constitutive constant values for all densities of a particular soil at all pressures. The 13 hypoplastic parameters used were calibrated through standard laboratory monotonic and cyclic triaxial and oedometer tests. Additional undrained triaxial and cyclic triaxial testing data that had not been used in the calibration process were used to validate the parameters.

Structural performance of buried pipeline undergoing strike-slip fault rupture in 3D using a non-linear sand model

Nonlinear structural response of buried continuous pipeline undergoing strike-slip fault rupture, i.e., where soil masses get displaced in the horizontal plane along a fault line, is studied in a detailed manner. A detailed analysis technique employing ABAQUS/Standard with implicit formulation to study the behavior of buried continuous pipelines crossing fault movements is proposed and established with suitable validations. A three-dimensional nonlinear finite element (FE) model including both material and geometric nonlinearities is used for this study. Firstly, a non-linear sand constitutive model is adopted and implemented in commercial FE package ABAQUS. The adopted material model is validated with available experimental tri-axial test results. This material model is thereafter suitably calibrated to develop a FE model of buried pipeline undergoing fault rupture for a specific large-scale experimental test. The study identified important soil strength parameters from direct shear soil tests conducted for the large-scale test program and converted them suitably with respect to the adopted sand constitutive model. The FE model is then validated against full-scale experimental results. It is observed that the developed FE model yields highly accurate results in comparison to available numerical results for this experiment. Analysis results indicated that, consideration of sand non-linear mobilized shear strength appropriately in numerical modelling may result in significantly improved prediction of generated pipeline strains with increasing fault displacements.

SANISAND-F: Sand constitutive model with evolving fabric anisotropy

In order to incorporate the very important role of evolving fabric anisotropy on the mechanical response of sand, a constitutive model is developed within the frameworks of Bounding Surface plasticity and Anisotropic Critical State Theory in multiaxial stress space. The main new constitutive ingredient is a fabric anisotropy variable A, a scalar measure of the relative orientation between an evolving fabric tensor F and the deviatoric plastic strain rate direction. The variable A affects scalar ingredients of the model quantifying the plastic strain rate, i.e. the plastic modulus and the dilatancy. A comprehensive calibration procedure is fully described and an extensive validation is performed against a very large dataset from 55 monotonic element tests on Toyoura sand provided by various laboratories, loaded under drained and undrained conditions. The introduction of A into the model is the main reason why successful simulation of data is achieved for loading at various orientations of the stress tensor under otherwise same initial conditions of void ratio and confining pressure, and this even if the data often exhibit huge difference of response because of the difference in loading orientation.

Effects of Construction Sequences and Volume Loss on Perpendicularly Crossing Tunnels

The number of constructed tunnels has been gradually increasing for the past decades due to rapid development in urban areas. However, the soil‐structure interaction problems arising from perpendicularly crossing tunnels attract relatively little research attention in the past. In this study, six three‐dimensional finite element analyses were conducted to simulate tunnel excavation nearby a perpendicularly crossing existing tunnel, in an attempt to investigate the effects of construction sequences on cross‐cutting tunnels. The hypoplastic constitutive model for sand is adopted in the numerical analysis to consider the soil small‐strain stiffness. Computed results are presented and discussed in terms of ground surface settlement, displacement and deformation of the existing tunnel, and bending moment induced on the existing tunnel. The stress‐transfer mechanism in soil nearby the existing tunnel due to tunnelling is also studied.

GPU optimization of material point methods

The Material Point Method (MPM) has been shown to facilitate effective simulations of physically complex and topologically challenging materials, with a wealth of emerging applications in computational engineering and visual computing. Borne out of the extreme importance of regularity, MPM is given attractive parallelization opportunities on high-performance modern multiprocessors. Parallelization of MPM that fully leverages computing resources presents challenges that require exploring an extensive design-space for favorable data structures and algorithms. Unlike the conceptually simple CPU parallelization, where the coarse partition of tasks can be easily applied, it takes greater effort to reach the GPU hardware saturation due to its many-core SIMT architecture. In this paper we introduce methods for addressing the computational challenges of MPM and extending the capabilities of general simulation systems based on MPM, particularly concentrating on GPU optimization. In addition to our open-source high-performance framework, we also conduct performance analyses and benchmark experiments to compare against alternative design choices which may superficially appear to be reasonable, but can suffer from suboptimal performance in practice. Our explicit and fully implicit GPU MPM solvers are further equipped with a Moving Least Squares MPM heat solver and a novel sand constitutive model to enable fast simulations of a wide range of materials. We demonstrate that more than an order of magnitude performance improvement can be achieved with our GPU solvers. Practical high-resolution examples with up to ten million particles run in less than one minute per frame.

A state-dependent soil model and its application to principal stress rotation simulations

The plastic strain caused by principal stress rotation is one of the most important factors contributing to substantial deformation under earthquake, wave or traffic loading. The original Pastor–Zienkiewicz Mark III model, a well-known model for the analysis of the dynamic response under cyclic loading, is unable to consider the effects of principal stress orientation as well as state-dependent dilatancy. In this article, a new constitutive model for sand is developed to consider both aforementioned effects based on the original Pastor–Zienkiewicz Mark III model. There are 14 model parameters in total for the static condition and three extra parameters for cyclic loading, and a corresponding calibration method of model parameters is proposed. The predictive capability of the proposed model is verified with the results of a series of experiments on sand, including undrained monotonic tests in different fixed principal stress orientations and undrained cyclic rotational shear tests. The comparisons indicate that the proposed model can effectively incorporate the effects of principal stress orientation and state-dependent dilatancy.

Application of Nor Sand Constitutive Model in a Highway Fill Embankment Slope Stability Failure Study

This paper presents a case study of a static load induced liquefaction in a simple roadway widening project constructed in north eastern part of Ohio in 2008. The widening required an embankment fill, which moved nearly 4 feet vertically and 1 foot laterally after two days of installation. The main objective of the work is to demonstrate how a simple Constitutive model, in this case Nor Sand model, can represent the static liquefaction in loose sand layers under specific conditions. A set of parameters is assumed based on the soil properties and an Excel Spreadsheet is used for simulations of triaxial compression of sand. It was considered that the situation which led to the failure, and the situation after the solution adopted. Moreover, slope stability analysis is provided for validation of the original results using a commercial software. It was found that the model can represent through stress strain curves and stress paths the behavior of the soil layer which led to the embankment fill movement. As the original work considered only slope stability analysis to explain this phenomenon, the present study shows a different approach for the case study, and this is the main contribution of this research.

An Efficient Generalized Plasticity Constitutive Model with Minimal Complexity and Required Parameters

Numerical analyses precision performed by software, depends mostly on the accuracy of constitutive model. Therefore, the issue of accuracy has led to significant achievements in the development of constitutive models simulating the mechanical behavior of soils. However, these constitutive models often needs to a lot of parameters to be calibrated for each type of soil, and it’s considered as a disadvantage. especially, when the model parameters should be obtained through trial and error, the number of the parameters becomes a considerable issue. This paper presents an advanced constitutive model. Despite requiring much lower number of model parameters, it provides the same level of accuracy in compression of other advanced constitutive models for sand in literature. To show that the presented model achieved to this purpose, it is evaluated by various experimental data and some predictions made by two successful advanced models in literature. Consequently, it shows the presented model can accurately predict the sand behavior under different conditions despite using smaller number of parameters. Also, the accuracy of the presented model is on a par with advanced constitutive models available in the geotechnical engineering literature.

Numerical prediction of circular tunnel seismic behaviour using hypoplastic soil constitutive model

Numerical simulation of the centrifuge experiment with dynamic loading on a small scale circular tunnel model surrounded by dry Buzzard sand is being presented. Considering soil dynamic behaviour properly, analyses were performed using an advanced hypoplastic constitutive model for sands considering the intergranular strain. The results include: settlement, lining forces time histories and peak acceleration in normalized model depth, were in good agreement with experimental data. Additional numerical modelling have been performed using hardening soil model with small-strain stiffness (HSS) and Mohr–Coulomb criteria (MC), then the results compared in detail with the hypoplastic (HP) model. The finite element predictions of settlement time histories and the internal forces mobilized in the tunnel lining were compared and the results declared that although settlements were underestimated by all models, HP has shown better responses in following the experimental trend. Also, internal forces obtained by the HP model showed smaller reversible variations.

Multi-species simulation of porous sand and water mixtures

We present a multi-species model for the simulation of gravity driven landslides and debris flows with porous sand and water interactions. We use continuum mixture theory to describe individual phases where each species individually obeys conservation of mass and momentum and they are coupled through a momentum exchange term. Water is modeled as a weakly compressible fluid and sand is modeled with an elastoplastic law whose cohesion varies with water saturation. We use a two-grid Material Point Method to discretize the governing equations. The momentum exchange term in the mixture theory is relatively stiff and we use semi-implicit time stepping to avoid associated small time steps. Our semi-implicit treatment is explicit in plasticity and preserves symmetry of force linearizations. We develop a novel regularization of the elastic part of the sand constitutive model that better mimics plasticity during the implicit solve to prevent numerical cohesion artifacts that would otherwise have occurred. Lastly, we develop an improved return mapping for sand plasticity that prevents volume gain artifacts in the traditional Drucker-Prager model.