scholarly journals Enhancing Constitutive Models for Soils: Adding the Capability to Model Nonlinear Small Strain in Shear

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
S. Seyedan ◽  
W. T. Sołowski
Keyword(s):  
Yield Surface ◽  
Constitutive Models ◽  
Strain Range ◽  
Small Strain ◽  
Deviatoric Stress ◽  
Triaxial Tests ◽  
Engineering Practice ◽  
Model Parameters ◽  
Highly Nonlinear ◽  
Strain Relationship

The deviatoric stress-deviatoric strain relationship in soils is highly nonlinear, especially in the small strain range. However, the constitutive models which aim to replicate the small strain nonlinearity are often complex and rarely used in geotechnical engineering practice. The goal of this study is to offer a simple way for updating the existing constitutive models, widely used in geotechnical practice, to take into account the small strain shear modulus changes. The study uses an existing small strain relationship to derive a yield surface. When the yield surface is introduced to an existing soil model, it enhances the model with the nonlinear deviatoric stress-deviatoric strain relationship in the small strain range. The paper also gives an example of such a model enhancement by combining the new yield surface with the Modified Cam Clay constitutive model. The validation simulations of the undrained triaxial tests on London Clay and Ham River sand with the upgraded constitutive models replicate the experiments clearly better than the base models, without any changes to existing model parameters and the core source code associated with the base model.

Enhanced in Situ Geotechnical Testing for Bridge Foundation Analysis

1997 ◽  
Vol 1569 (1) ◽  
pp. 26-35 ◽  
Author(s):  
Paul W. Mayne ◽  
Chris Dumas
Keyword(s):  
Continuum Theory ◽  
Strain Range ◽  
Small Strain ◽  
Standard Penetration Test ◽  
Engineering Properties ◽  
Engineering Practice ◽  
Time Behavior ◽  
Highly Nonlinear ◽  
Hybrid Devices

Geotechnical analyses of bridge foundations are complex because of the difficulties in addressing the highly nonlinear and anisotropic stress-strain-strength-time behavior of soils, from the nondestructive small-strain range region through to failure conditions. Often engineering practice overrelies on a single test value from soil borings [the standard penetration test (SPT) N-value] for the evaluation of all necessary geotechnical parameters, which is unrealistic. There exists, in fact, a variety of in situ measurement devices for the better definition of soil engineering properties, particularly hybrid devices such as the seismic piezocone and seismic flat dilatometer, as related to foundation applications. The importance of small-strain field stiffness measurements (i.e., shear wave velocity) is discussed and illustrated with two case studies involving the axial response of drilled shaft and driven pile foundations. The examples are reviewed within the context of elastic continuum theory but may be applied similarly for use in site-specific determinations of nonlinear spring constants and well-known t-z, p-y, or q-z curves, or all three.

A Structural Continuum Constitutive Model for a Two-Phase Soft Tissue

2010 ◽  
Author(s):  
Silvia Wognum ◽  
Michael S. Sacks
Keyword(s):  
Mechanical Behavior ◽  
Soft Tissues ◽  
Bladder Wall ◽  
Constitutive Models ◽  
Tissue Level ◽  
Model Parameters ◽  
Two Phase ◽  
Tissue Properties ◽  
Highly Nonlinear ◽  
Cord Injury

Due to the complexity in determining multi-constituent tissue properties, most structural constitutive models for soft tissues focus on a single constituent. However, many tissues contain multiple load-bearing constituents, such as collagen fibers and smooth muscle (SM) cells. Moreover, to elucidate how observed changes in tissue components are related to altered net mechanical behavior at the tissue level, structural constitutive models require physiological relevant model parameters and formulations for changes in referential configuration when one component is physically removed. As an excellent example application that underscores these issues, we have examined the urinary bladder wall (UBW), which undergoes large deformations and exhibits highly nonlinear and anisotropic mechanical behavior [1,2]. Moreover, it undergoes profound remodeling in response to different pathologies such as spinal cord injury (SCI) [1,2].

scholarly journals Parameters of Sand-Tyre Chips Mixture for Hardening Soil Small Constitutive Model

2021 ◽  
Vol 1203 (2) ◽  
pp. 022067
Author(s):  
Magdalena Kowalska
Keyword(s):  
Constitutive Models ◽  
Small Strain ◽  
Bender Elements ◽  
Empirical Formulas ◽  
Anthropogenic Soils ◽  
Material Parameters ◽  
Compression Stiffness ◽  
Strain Relationship ◽  
Soil Behaviour ◽  
Hardening Soil Model

Abstract Hardening Soil model with the small strain extension (HSS) is lately one of the most popular constitutive models to describe soil behaviour. It is versatile – includes the phenomena of shear strength, stress history, dilatancy, volumetric and shear hardening, hyperbolic stress-strain relationship in axial compression, stiffness dependency on stress and its degradation with strain, as well as the regain of the high stiffness after sharp loading reversals. Even though the model is advanced and complex, accordingly to its authors, it is relatively easy to calibrate based on results of standard tests and empirical formulas. In this paper an attempt was undertaken to estimate the parameters of untypical anthropogenic soils – mixtures of sand and scrap tyre rubber in order to build a database for future numerical analyses. A literature review was conducted and, eventually, the material parameters were determined based on results of a series of laboratory tests (cyclic and monotonic triaxial with bender elements, direct shear) published by researchers of Wollongong University of Australia.

scholarly journals A Hypoelastic Dynamic Constitutive Model to Account for the Hysteretic Behaviour of Soil Subjected to Cyclic Loads

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Jian Li ◽  
Jianhua Guo ◽  
Zhangjun Dai ◽  
Lingfa Jiang ◽  
Shanxiong Chen
Keyword(s):  
Cyclic Load ◽  
Constitutive Models ◽  
Triaxial Tests ◽  
Cyclic Loads ◽  
Stress Strain ◽  
Integration Algorithm ◽  
Proposed Model ◽  
Strain Relationship ◽  
Static And Dynamic Loads ◽  
Three Stages

To reduce the difficulties associated with dynamic constitutive models, a model was established for soil in this study based on hypoelasticity. The stress-strain relationship in soil under a cyclic load was divided into three stages: initial loading, unloading, and reloading. The stress-strain relationship in each stage was ascertained using a hyperbolic equation. On this basis, the physical significance of the parameters in the model and their method of determination were described. The effects of the parameters on the stress-strain relationship were investigated and the integration algorithm of the model was established. Finally, the rationality of the proposed model was verified by conducting triaxial tests under conventional and cyclic loads. The results show that the model is able to adequately demonstrate all the stress-strain relations in the soil under both static and dynamic loads.

Experimental Study on Anisotropy of Granite Residual Soil

2012 ◽  
Vol 518-523 ◽  
pp. 4721-4725
Author(s):  
Li Qun Guo ◽  
Yao Xing Huang ◽  
Jian Bing Huang
Keyword(s):  
Pressure Coefficient ◽  
Specimen Size ◽  
Engineering Properties ◽  
Triaxial Tests ◽  
Engineering Practice ◽  
Residual Soil ◽  
Induced Anisotropy ◽  
Inherent Anisotropy ◽  
Strain Relationship ◽  
Granite Residual Soil

Inherent anisotropy and induced anisotropy are two main influencing factors on the engineering properties of granite residual soil. When preparing specimens of granite residual soil for undrained triaxial tests, large-sized specimens can be used to weaken the influence of sampling disturbance and inherent anisotropy, and K0 consolidation is adopted to restore the soil specimens to the state of induced anisotropy. The experimental results indicate that, specimen size has no significant influence on the determination of static lateral pressure coefficient k0, while specimen size and consolidation method obviously affect the stress-strain relationship and shear strength indices of granite residual soil. Undrained triaxial tests using large-sized specimens and the method of K0 consolidation can provide parameters more suitable for engineering practice.

Analysis of the Deformation Characteristics of Loess Based on Thermal–Mechanical Coupling under an Energy Internet

2021 ◽  
Author(s):  
Zengle Li ◽  
Bin Zhi ◽  
Enlong Liu
Keyword(s):  
Mechanical Properties ◽  
Temperature Change ◽  
Clean Energy ◽  
Model Parameters ◽  
Stress Strain ◽  
Energy Internet ◽  
Influence Of Temperature ◽  
Medium Model ◽  
Strain Relationship ◽  
Natural Loess

In response to the major challenges faced by China’s transition to green low-carbon energy under the dual-carbon goal, the use of energy Internet cross-boundary thinking will help to develop research on the integration of renewable clean energy and buildings. Energy piles are a new building-energy-saving technology that uses geothermal energy in the shallow soil of the Earth’s surface as a source of cold (heat) to achieve heating in winter and cooling in summer. It is a complex thermomechanical working process that changes the temperature of the rock and soil around the pile, and the temperature change significantly influences the mechanical properties of natural loess. Although the soil temperature can be easily and quickly obtained by using sensors connected to the Internet of Things, the mechanical properties of natural loess will change greatly under the influence of temperature. To explore the influence of temperature on the stress–strain relationship of structural loess, the undrained triaxial consolidation tests were carried out under different temperatures (5, 20, 50 and 70∘C) and different confining pressures (50, 100, 200 and 400[Formula: see text]kPa), and a binary-medium model was introduced to simulate the stress–strain relationship. By introducing the damage rate under temperature change conditions, a binary-medium model of structural loess under variable temperature conditions was established, and the calculation method of the model parameters was proposed. Finally, the calculated results were compared with the test results. The calculation results showed that the established model has good applicability.

Comprehensive global sensitivity analysis of a repository model using different types of transformations and metamodeling techniques

2021 ◽  
Author(s):  
Sabine M. Spiessl ◽  
Dirk-A. Becker ◽  
Sergei Kucherenko
Keyword(s):  
Sensitivity Analysis ◽  
Global Sensitivity Analysis ◽  
Higher Order ◽  
Model Parameters ◽  
High Dimensional Model Representation ◽  
Model Output ◽  
Global Sensitivity ◽  
Sparse Polynomial ◽  
Sensitivity Indices ◽  
Highly Nonlinear

<p>Due to their highly nonlinear, non-monotonic or even discontinuous behavior, sensitivity analysis of final repository models can be a demanding task. Most of the output of repository models is typically distributed over several orders of magnitude and highly skewed. Many values of a probabilistic investigation are very low or even zero. Although this is desirable in view of repository safety it can distort the evidence of sensitivity analysis. For the safety assessment of the system, the highest values of outputs are mainly essential and if those are only a few, their dependence on specific parameters may appear insignificant. By applying a transformation, different model output values are differently weighed, according to their magnitude, in sensitivity analysis. Probabilistic methods of higher-order sensitivity analysis, applied on appropriately transformed model output values, provide a possibility for more robust identification of relevant parameters and their interactions. This type of sensitivity analysis is typically done by decomposing the total unconditional variance of the model output into partial variances corresponding to different terms in the ANOVA decomposition. From this, sensitivity indices of increasing order can be computed. The key indices used most often are the first-order index (SI1) and the total-order index (SIT). SI1 refers to the individual impact of one parameter on the model and SIT represents the total effect of one parameter on the output in interactions with all other parameters. The second-order sensitivity indices (SI2) describe the interactions between two model parameters.</p><p>In this work global sensitivity analysis has been performed with three different kinds of output transformations (log, shifted and Box-Cox transformation) and two metamodeling approaches, namely the Random-Sampling High Dimensional Model Representation (RS-HDMR) [1] and the Bayesian Sparse PCE (BSPCE) [2] approaches. Both approaches are implemented in the SobolGSA software [3, 4] which was used in this work. We analyzed the time-dependent output with two approaches for sensitivity analysis, i.e., the pointwise and generalized approaches. With the pointwise approach, the output at each time step is analyzed independently. The generalized approach considers averaged output contributions at all previous time steps in the analysis of the current step. Obtained results indicate that robustness can be improved by using appropriate transformations and choice of coefficients for the transformation and the metamodel.</p><p>[1] M. Zuniga, S. Kucherenko, N. Shah (2013). Metamodelling with independent and dependent inputs. Computer Physics Communications, 184 (6): 1570-1580.</p><p>[2] Q. Shao, A. Younes, M. Fahs, T.A. Mara (2017). Bayesian sparse polynomial chaos expansion for global sensitivity analysis. Computer Methods in Applied Mechanics and Engineering, 318: 474-496.</p><p>[3] S. M. Spiessl, S. Kucherenko, D.-A. Becker, O. Zaccheus (2018). Higher-order sensitivity analysis of a final repository model with discontinuous behaviour. Reliability Engineering and System Safety, doi: https://doi.org/10.1016/j.ress.2018.12.004.</p><p>[4] SobolGSA software (2021). User manual https://www.imperial.ac.uk/process-systems-engineering/research/free-software/sobolgsa-software/.</p>

A finite-deformation constitutive model of particle-binder composites incorporating yield-surface-free plasticity

2021 ◽  
pp. 1-32
Author(s):  
Ankit Agarwal ◽  
Marcial Gonzalez
Keyword(s):  
Constitutive Model ◽  
Yield Surface ◽  
Finite Deformation ◽  
Large Strain ◽  
Elastic Response ◽  
Rate Equations ◽  
Internal Variables ◽  
Model Parameters ◽  
Stress Strain ◽  
Stress Softening

Abstract We present a constitutive model for particle-binder composites that accounts for finite-deformation kinematics, nonlinear elasto-plasticity without apparent yield, cyclic hysteresis, and progressive stress-softening before the attainment of stable cyclic response. The model is based on deformation mechanisms experimentally observed during quasi-static monotonic and cyclic compression of mock Plastic-Bonded Explosives (PBX) at large strain. An additive decomposition of strain energy into elastic and inelastic parts is assumed, where the elastic response is modeled using Ogden hyperelasticity while the inelastic response is described using yield-surface-free endochronic plasticity based on the concepts of internal variables and of evolution or rate equations. Stress-softening is modeled using two approaches; a discontinuous isotropic damage model to appropriately describe the softening in the overall loading-unloading response, and a material scale function to describe the progressive cyclic softening until cyclic stabilization. A nonlinear multivariate optimization procedure is developed to estimate the elasto-plastic model parameters from nominal stress-strain experimental compression data. Finally, a correlation between model parameters and the unique stress-strain response of mock PBX specimens with differing concentrations of aluminum is identified, thus establishing a relationship between model parameters and material composition.

Shear strength and yield surface of a partially saturated sandy silt under generalized stress states

2021 ◽  
Author(s):  
Rodrigo Carreira Weber ◽  
Enrique E. Romero Morales ◽  
Antonio Lloret
Keyword(s):  
Shear Strength ◽  
Yield Surface ◽  
Experimental Results ◽  
Model Parameters ◽  
Hollow Cylinder Apparatus ◽  
Clayey Silt ◽  
Lode Angle ◽  
Yield Surfaces ◽  
Stress States ◽  
Deviatoric Stresses

This paper studies the hydromechanical behavior of a slightly compacted mixture of sand and clayey silt (30%/70%) under a generalized stress state. The experimental study focused on analyzing the yielding response and shear strength behavior at different stress states (characterized by the intermediate principal stress parameter b, or Lode angle) and at different initial total suctions (as-compacted state). For the investigation, a hollow cylinder apparatus was used. The shear strength results allowed defining the variation of the critical state line with the Lode angle and the suction. Different models were proposed for isotropic and anisotropic yield surfaces, and their shape and rotation were calibrated with experimental results. The modeled yield surfaces fitted reasonably well the experimental results, considering their inclination and dependence on the suction, mean and deviatoric stresses and Lode angle. In addition, some relationships between the stresses and the model parameters were proposed to normalize the yield surface equation.

Thermodynamic-based cross-scale model for structural soil with emphasis on bond dissolution

2021 ◽  
Author(s):  
Wei Zhang ◽  
Jia-qiang Zou ◽  
Kang Bian ◽  
Yang Wu
Keyword(s):  
Constitutive Model ◽  
Bond Strength ◽  
Scale Model ◽  
Triaxial Tests ◽  
Natural Soil ◽  
Engineering Practice ◽  
Compression Tests ◽  
Strength Deterioration ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

The immersion weakening effect of natural soil has always been a difficult problem encountered in geotechnical engineering practice. The bond dissolution is a common cause of soil strength deterioration, which remains not well understood yet. In this study, a thermodynamic-based constitutive model of structural soils based on the α model is first established, considering the bond strength by modifying the yield surface size and gradually reducing the bond strength with the development of plastic strain. Furthermore, by taking the meso-mechanisms of bond dissolution into account, the evolution rule of the free energy during the bond dissolution process is derived based on a homogenization approach, and a thermodynamic-based constitutive model of structural soil with bond dissolution is thereafter developed. By comparing with the results of one-dimensional compression tests and conventional triaxial tests, the model is verified to be capable of reflecting the gradual destructuration process of soil while loading. The comparison with triaxial test results of completely decomposed granite after different immersion durations and parametric studies show that based on the cross-scale energy equivalence, the model can well reflect the strength deterioration characteristics of completely decomposed granite with bond dissolution mechanisms at the mesoscale fully considered.

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