scholarly journals Plastic anisotropy of soft reconstituted clays

2008 ◽  
Vol 45 (3) ◽  
pp. 314-328 ◽  
Author(s):  
Minna Karstunen ◽  
Mirva Koskinen
Keyword(s):  
Stress Ratio ◽  
Plastic Anisotropy ◽  
Stress Path ◽  
Test Results ◽  
Fabric Anisotropy ◽  
Induced Anisotropy ◽  
Modified Cam Clay ◽  
Model Predictions ◽  
Elastoplastic Constitutive Model ◽  
Cam Clay

The aim of the paper is to extend the experimental validation of the S-CLAY1 model, which is a recently proposed elastoplastic constitutive model that accounts for initial and plastic strain-induced anisotropy. Drained stress path controlled tests were performed on reconstituted samples of four Finnish clays to study the effects of anisotropy in the absence of the complexities of structure present in natural undisturbed clays. Each test involved several loading, unloading, and reloading stages with different values of stress ratio and, hence, induced noticeable changes in the fabric anisotropy. Comparisons between test results and model predictions with the S-CLAY1 model and the modified Cam clay model demonstrate that despite its simplicity, the S-CLAY1 model can provide excellent predictions of the behaviour of unstructured soil.

scholarly journals Experimental Study of Silty Clay Plane Strain Tri-axial Test under RTC Path and Modified Cam-clay Model

2018 ◽  
Vol 4 (3) ◽  
pp. 518
Author(s):  
Tao Cheng ◽  
Yi Zhang ◽  
Keqin Yan
Keyword(s):  
Plane Strain ◽  
Stress Path ◽  
Physical Parameters ◽  
Silty Clay ◽  
Model Framework ◽  
Loading Test ◽  
Clay Model ◽  
Modified Cam Clay ◽  
Institute Of Technology ◽  
Cam Clay

The character of geomaterials is affected by stress path remarkably. Under different stress paths, the stress-strain characteristics of geomaterials are difference. For the unloading path in existing engineering situation, the physical parameters and constitutive model is usually determined by loading test. The path to uninstall the actual project conditions which may be a larger error. Therefore, this work proceeding from the actual project, deep excavation of the lateral unloading condition is analysed. The tests of CTC path and RTC path on silty clay in Huangshi city of china by multi-path tri-axial plane strain are carried on in the geotechnical Engineering Laboratory of Huangshi Institute of Technology. Then, the phenomenon under the two stress paths are compared with each other and describing the differences between them. The mechanical properties in the RTC stress path is analyzed mainly. Based on the Cam-Clay model framework, then derived this material yield equation based on Cam-clay model, Laiding the foundation for the numerical analysis.

An anisotropic elastoplastic model for soft clays

2003 ◽  
Vol 40 (2) ◽  
pp. 403-418 ◽  
Author(s):  
Simon J Wheeler ◽  
Anu Näätänen ◽  
Minna Karstunen ◽  
Matti Lojander
Keyword(s):  
Experimental Data ◽  
Yield Curve ◽  
Constitutive Relations ◽  
Stress Path ◽  
Elastoplastic Model ◽  
Soft Clays ◽  
Rotational Hardening ◽  
Modified Cam Clay ◽  
Cam Clay

An anisotropic elastoplastic model for soft clays is presented. Experimental data from multistage drained triaxial stress path tests on Otaniemi clay from Finland provide support for the proposed shape of the yield curve and for the proposed relationship describing the change of yield curve inclination with plastic straining. Procedures are proposed for determining the initial inclination of the yield curve and the values of the two additional soil constants within the model. Comparisons of model simulations with experimental data demonstrate significant improvements in the performance of the new model over the Modified Cam Clay model. The remaining discrepancies are mainly attributable to the important role of destructuration in the sensitive Otaniemi clay.Key words: anisotropy, constitutive relations, elastoplasticity, laboratory tests, rotational hardening, soft clays.

Simulation of Natural Pisa Clay Using an Enhanced Anisotropic Elastoplastic Bounding Surface Model

2013 ◽  
Vol 80 (2) ◽  
Author(s):  
Jianhong Jiang ◽  
Hoe I. Ling ◽  
Victor N. Kaliakin
Keyword(s):  
Plastic Anisotropy ◽  
Complex Stress ◽  
Surface Model ◽  
Test Results ◽  
Compression Tests ◽  
Bounding Surface ◽  
Proportional Loading ◽  
Model Predictions ◽  
Loading Tests ◽  
Basic Features

The experimental behavior of natural Pisa clay under complex stress paths is simulated by an enhanced anisotropic elastoplastic bounding surface model. In its present application, the model has nine parameters and focuses on the basic features of clay behavior, such as yielding, critical state, overconsolidation and plastic anisotropy. The model is first calibrated against the test results obtained from tri-axial compression tests and subsequently used to predict the behavior of true tri-axial tests. The overall agreement between the model predictions and the experimental data is very good for proportional loading tests in both meridional and deviatoric stress spaces. The result of prediction is also compared with the original simulations that were conducted by an advanced clay model.

A Graphical Analysis-based Method for Undrained Cylindrical Cavity Expansion in Modified Cam Clay Soil

Géotechnique ◽  
2022 ◽  
pp. 1-35
Author(s):  
S. L. Chen ◽  
Y. N. Abousleiman
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Cylindrical Cavity ◽  
Clay Soil ◽  
Stress Path ◽  
Graphical Analysis ◽  
Material Point ◽  
Modified Cam Clay ◽  
Deviatoric Plane ◽  
Cam Clay

A novel graphical analysis-based method is proposed for analysing the responses of a cylindrical cavity expanding under undrained conditions in modified Cam Clay soil. The essence of developing such an approach is to decompose and represent the strain increment/rate of a material point graphically into the elastic and plastic components in the deviatoric strain plane. It allows the effective stress path in the deviatoric plane to be readily determined by solving a first-order differential equation with the Lode angle being the single variable. The desired limiting cavity pressure and pore pressure can be equally conveniently evaluated, through basic numerical integrations with respect to the mean effective stress. Some ambiguity is clarified between the generalized (work conjugacy-based) shear strain increments and the corresponding deviatoric invariants of incremental strains. The present graph-based approach is also applicable for the determination of the stress and pore pressure distributions around the cavity. When used for predicting the ultimate cavity/pore pressures, it is computationally advantageous over the existing semi-analytical solutions that involve solving a system of coupled governing differential equations for the effective stress components. It thus may serve potentially as a useful and accurate interpretation of the results of in-situ pressuremeter tests on clay soils.

Undrained anisotropy of Hostun RF loose sand: new experimental investigations

2006 ◽  
Vol 43 (11) ◽  
pp. 1195-1212 ◽  
Author(s):  
Zeina Finge ◽  
Thiep Doanh ◽  
Phillippe Dubujet
Keyword(s):  
Effective Stress ◽  
Stress Ratio ◽  
Triaxial Compression ◽  
Stress Path ◽  
Experimental Investigations ◽  
Loose Sand ◽  
Induced Anisotropy ◽  
Static Liquefaction ◽  
Stress States ◽  
Effective Stress Ratio

The undrained behaviour of loose and overconsolidated Hostun RF sand in triaxial compression and extension tests is described. The samples are isotropically or anisotropically overconsolidated along several constant effective stress ratio paths with various overconsolidation ratios (OCR), up to 24. To minimize the effect of variation of density on the observed undrained behaviour, all tested samples are required to have a nearly identical void ratio before the final monotonic undrained shearing. Isotropically overconsolidated and normally consolidated samples exhibit the same phenomenon of partial static liquefaction, but anisotropically overconsolidated specimens reveal a completely different undrained behaviour. A common pseudoelastic response is observed for a given overconsolidation history. This response is induced by recent stress history in terms of effective stress paths, independent of the OCR during overconsolidation. The initial gradient of the effective stress paths seems to depend solely on the direction of the previous linear stress path history. This paper offers a comprehensive understanding of the mechanism of the induced anisotropy of loose sand created by simple linear stress paths from three different initial stress states in the classical triaxial plane. The pseudoelastic response can be adequately modelled by a simple hyperelastic component of the elastoplastic framework.Key words: induced anisotropy, overconsolidation, instability, laboratory undrained tests, sand, hyperelasticity.

Design of shallow footings on heavily overconsolidated clays

2012 ◽  
Vol 49 (2) ◽  
pp. 184-196 ◽  
Author(s):  
Muniram Budhu
Keyword(s):  
Bearing Capacity ◽  
Shallow Foundations ◽  
Tensile Failure ◽  
Test Results ◽  
Load Bearing Capacity ◽  
Modified Cam Clay ◽  
Overconsolidated Clays ◽  
Stress Surface ◽  
Stress States ◽  
Cam Clay

This paper presents an integrated bearing capacity–settlement approach to the design of shallow foundations on heavily overconsolidated clays by alterations of the “modified Cam clay” (MCC) model. The bearing capacity of soils and their settlements from loads imposed on shallow footings have been studied extensively. Yet, there is no consensus on a method that provides both reliable load-bearing capacity and settlement predictions. Current methods treat the soil under shallow footings as different ideal materials for the purpose of calculating the bearing capacity and settlement. The method proposed in this paper treats the soil as a single ideal material for both bearing capacity and settlement. The MCC model is tailored by adding Hvorslev’s findings on overconsolidated clays and delineating stress states that bring the soil to tensile failure from those that cause it to yield or behave elastically or to show discontinuous response. A limiting stress surface is established as defining a limiting bearing capacity. A heavily overconsolidated clay is assumed to behave elastically if its stress state is below the limiting stress surface. Predictions from the method proposed in this paper compare favorably with model tests and field test results. Examples are provided illustrating how to use the proposed method.

scholarly journals COMPARISON AND APPLICATION OF DIFFERENT ELASTO-PLASTIC CONSTITUTIVE MODELS IN FEM ANALYSIS OF AN EXCAVATED SOIL SLOPE

2012 ◽  
Vol 18 (6) ◽  
pp. 802-810 ◽  
Author(s):  
Kunyong Zhang ◽  
Yingbo Ai
Keyword(s):  
Constitutive Models ◽  
Fem Analysis ◽  
Stress Path ◽  
Soil Slope ◽  
Modified Model ◽  
Stress Ratio Parameter ◽  
Modified Cam Clay ◽  
Frame Work ◽  
Reasonable Description ◽  
Cam Clay

A modified anisotropic elasto-plastic model is presented in this paper based on the frame work of Modified Cam-clay model and Original Sekiguchi-Ohta model by applying a new stress ratio parameter, through which the yield locus and hardening axis in the p-q plane were adjusted to give a more reasonable description of the practical excavation stress path from initial K0 state. Typical excavated soil slope was selected as the illustration example to carry out the finite element numerical analysis by applying four constitutive models (Original Cam-Clay, Modified Cam-Clay, Original Sekiguchi-Ohta and Modified Sekiguchi-Ohta). The calculated displacements of the slope with above different constitutive models were then compared with the measured infield data. It was found the field measured data agree better with the results calculated from modified model, which indicates that the modified anisotropic model is more suitable in the description of the stress path of excavated soils slope after K0 consolidation.

Compliant Pantographs via the Pseudo-Rigid-Body Model

1998 ◽  
Author(s):  
Andrew J. Nielson ◽  
Larry L. Howell
Keyword(s):  
Rigid Body ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Test Results ◽  
Rigid Link ◽  
Body Model ◽  
Design Flexibility ◽  
Model Predictions ◽  
Rigid Body Model ◽  
Classical Mechanism

Abstract This paper uses a familiar classical mechanism, the pantograph, to demonstrate the utility of the pseudo-rigid-body model in the design of compliant mechanisms to replace rigid-link mechanisms, and to illustrate the advantages and limitations of the resulting compliant mechanisms. To demonstrate the increase in design flexibility, three different compliant mechanism configurations were developed for a single corresponding rigid-link mechanism. The rigid-link pantograph consisted of six links and seven joints, while the corresponding compliant mechanisms had no more than two links and three joints (a reduction of at least four links and four joints). A fourth compliant pantograph, corresponding to a rhomboid pantograph, was also designed and tested. The test results showed that the pseudo-rigid-body model predictions were accurate over a large range, and the mechanisms had displacement characteristics of rigid-link mechanisms in that range. The limitations of the compliant mechanisms included reduced range compared to their rigid-link counterparts. Also, the force-deflection characteristics were predicted by the pseudo-rigid-body model, but they did not resemble those for a rigid-link pantograph because of the energy storage in the flexible segments.

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