Constitutive modeling of gassy sand behaviour

2005 ◽  
Vol 42 (3) ◽  
pp. 812-829 ◽  
Author(s):  
J LH Grozic ◽  
S MR Imam ◽  
P K Robertson ◽  
N R Morgenstern
Keyword(s):  
Constitutive Model ◽  
Constitutive Modeling ◽  
Pressure Change ◽  
Soil Liquefaction ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Loose Sand ◽  
Modified Model ◽  
Effective Normal Stress ◽  
Wide Range

The behaviour of loose gassy sand was investigated with the use of a constitutive model. The constitutive model was modified from an existing model that focused on assessing the liquefaction of loose sands over a wide range of states and loading conditions. The modifications involved taking into account the compressibility and solubility of the pore gas and liquids. Hilf's equation, which calculates the pore-pressure change in a gassy or unsaturated soil subjected to an applied total stress, was incorporated into the model formulation. The initial degree of saturation is needed for model prediction, and the coefficient of volumetric solubility (Henry's constant) was introduced as a new model parameter. The modified model was used to predict the effect of gas on the undrained static behaviour of loose sand. The laboratory results of saturated specimens were modeled, and the predicted and observed behaviours were found to agree well. Results from gassy specimens were also predicted, and again the model predictions matched the test results. The model was used to confirm that gas has the effect of decreasing, but not eliminating, the susceptibility of loose sand to flow liquefaction. The major shortcoming of the modified model was its inability to predict the slight increase in effective normal stress that was observed in the initial stages of all the undrained triaxial tests. This shortcoming resulted in differences between the predicted and observed behaviour especially of strain-hardening specimens.Key words: gassy soil, liquefaction, constitutive modeling, triaxial testing.

Modeling of the Cyclic Behavior of Loose Sand by an Elasto-Plastic Fuzzy Set Model

2013 ◽  
Vol 639-640 ◽  
pp. 708-713
Author(s):  
Cheng Chen ◽  
Li Wei Kong ◽  
Quan Qing Wang ◽  
Zhong Liu
Keyword(s):  
Constitutive Model ◽  
Fuzzy Set ◽  
Soil Mechanics ◽  
Cyclic Behavior ◽  
Cyclic Plasticity ◽  
Triaxial Tests ◽  
Loose Sand ◽  
Cyclic Triaxial Tests ◽  
Repeated Load ◽  
Cyclic Plasticity Model

The paper focuses on the development of a cyclic plasticity model based on the fuzzy set theory, which is implemented as a computational tool in order to simplify the computer programming of the constitutive driver. The constitutive model is a rate independent elasto-plastic model which is capable of describing repeated load cycles, dilatancy, material memory, and critical state soil mechanics features. Also, with the aid of membership function, the validity of the constitutive model is enhanced by comparing the theoretical output with a set of experimental data obtained from a variety of cyclic triaxial tests of loose sand.

scholarly journals Destructuration of saturated natural loess: From experiments to constitutive modeling

2020 ◽  
pp. 105678952093930
Author(s):  
Yukai Fu ◽  
Zhiwei Gao ◽  
Yi Hong ◽  
Tonglu Li ◽  
Akhil Garg
Keyword(s):  
Constitutive Model ◽  
Constitutive Modeling ◽  
Soil Structure ◽  
Triaxial Compression ◽  
Structural Effect ◽  
Triaxial Tests ◽  
Natural Soil ◽  
Special Focus ◽  
Compression Tests ◽  
Natural Loess

It has been well recognized that unsaturated natural loess shows significant volume contraction upon wetting due to its metastable internal structure. But the structural effect on stress–strain relationship of saturated natural (undisturbed) loess is much less explored. Few attempts have been made in proposing a constitutive model for saturated natural loess. This study presents both laboratory tests and constitutive modeling of a saturated natural loess, with special focus on the structural effect and evolution of structure damage during loading. Oedometer and drained triaxial compression tests have been carried out on undisturbed and remolded saturated loess samples. It is found that the natural soil structure has dramatic influence on mechanical behavior of loess, including the compressibility, dilatancy, and shear strength. Destructuration, which is the damage of soil structure with deformation, is observed in both oedometer and triaxial tests. A constitutive model is proposed for saturated loess based on the experimental observations. The model is established within the theoretical framework of subloading and superloading surface concepts. Destructuration of loess is assumed to be affected by both plastic volumetric and shear strain. A new method for determining the initial degree of structure is proposed. The model can reasonably predict the compression and shear behavior of both undisturbed and remolded saturated loess.

A critical-state constitutive model for liquefiable sand

2005 ◽  
Vol 42 (3) ◽  
pp. 830-855 ◽  
Author(s):  
SM Reza Imam ◽  
Norbert R Morgenstern ◽  
Peter K Robertson ◽  
David H Chan
Keyword(s):  
Constitutive Model ◽  
Critical State ◽  
Stress Ratio ◽  
Large Strain ◽  
Triaxial Compression ◽  
Loose Sand ◽  
Inherent Anisotropy ◽  
Dense Sand ◽  
Peak Point ◽  
Wide Range

This paper presents a critical-state constitutive model for sands over a wide range of void ratios and consolidation pressures in a triaxial plane. A single set of parameters, including a unique critical-state line reached at large strain, is also used in the model, and differences in behavior in triaxial compression and extension are modeled by accounting for anisotropy at small and medium ranges of strain. The model uses a capped yield surface (YS), which is characterized by its size and shape. Following evidence in past literature, the stress ratio at the peak point of the capped YS of loose sands is approximated by the stress ratio measured at the peak point of their undrained effective stress path. Yielding parameters obtained using this stress ratio are also applied in modeling dense sand behavior and drained loading. These parameters account for the effects of inherent anisotropy, void ratio, and confining pressure on yielding stresses and are readily determined from laboratory tests, but further research is required on their determination from field data. The model accounts for stress-induced and inherent anisotropies, using different parameters, which develop and evolve independently. Emphasis is placed on proper modeling of aspects of loose sand behavior that affect their susceptibility to flow liquefaction.Key words: constitutive modeling, liquefaction, loose sand, critical state, dilatancy, hardening.

Volume–mass unsaturated soil constitutive model for drying–wetting under isotropic loading–unloading conditions

2011 ◽  
Vol 48 (2) ◽  
pp. 280-313 ◽  
Author(s):  
Hung Q. Pham ◽  
Delwyn G. Fredlund
Keyword(s):  
Constitutive Model ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Research Literature ◽  
Degree Of Saturation ◽  
Soil Conditions ◽  
Constitutive Relationships ◽  
Proposed Model ◽  
Wide Range

A rigorous volume–mass constitutive model is proposed for the representation of drying–wetting under isotropic loading–unloading conditions for unsaturated soils. The proposed model utilizes concepts arising from soil physics and geotechnical engineering research and requires readily obtainable soils data for soil properties. The model can be used to predict void ratio and water content constitutive relationships (and therefore degree of saturation) for a wide range of unsaturated soils. Various stress paths (i.e., loading–unloading and drying–wetting) can be simulated, and hysteresis associated with the soil-water characteristic curve is taken into account. Two closed-form equations for the volume–mass constitutive relationships are presented for soils starting from slurry conditions. A number of test results (i.e., from experimental programs reported in the research literature) were used during the verification of the proposed volume–mass constitutive model. The volume–mass constitutive model captures key unsaturated soil conditions such as air-entry value, water-entry value, and residual conditions. The proposed model appears to satisfactorily predict unsaturated soil behavior for soils ranging from low compressible sands to high compressible clays.

Stress–dilatancy in very loose sand

2004 ◽  
Vol 41 (5) ◽  
pp. 972-989 ◽  
Author(s):  
Ken Been ◽  
Michael Jefferies
Keyword(s):  
Stress Ratio ◽  
Triaxial Compression ◽  
Constitutive Relations ◽  
Soil Liquefaction ◽  
Fundamental Aspect ◽  
Triaxial Tests ◽  
Loose Sand ◽  
Dense Sand ◽  
Stress Criterion ◽  
Undrained Strength

Virtually all investigation of liquefaction has used undrained tests, and it has become common to represent the undrained strength in terms of a collapse surface or collapse stress ratio described by an effective friction angle. A difficulty with undrained tests is that they only allow observation of the interaction of elastic and plastic strain because of the imposed boundary condition (i.e., no drainage or zero volume change), precluding a proper understanding of an effective stress criterion for maximum undrained strength. Drained triaxial tests do not suffer from this shortcoming, and stress–dilatancy of dense sands in drained shear is well established as a fundamental aspect of sand behaviour, based on micromechanical considerations. It is particularly interesting to consider the stress–dilatancy behaviour of very loose sands in the context of soil liquefaction. Although there are some data in the literature on loose sand behaviour in drained triaxial compression, the majority of data are actually for sands markedly denser than sands showing static liquefaction in undrained tests. This paper therefore reports some laboratory testing of very loose sands, together with comparative undrained liquefaction data, and compares the loose behaviour to that of dense sand. These data are reduced to stress–dilatancy form so that the fundamental aspects of loose soil behaviour can be seen and compared to flow rules used in constitutive models. The stress–dilatancy of very loose sand shows no limiting stress ratio markedly less than that of the critical state. Moreover, the stress–dilatancy trends of very loose sand are the same as those of dense sand. There is no evidence of "structural collapse" of the particulate arrangement of very loose sands, contrary to speculation associated with collapse surfaces in the literature. Explanations of sand liquefaction must seek other physical explanations of the soil behaviour.Key words: sand, constitutive relations, plasticity, liquefaction.

scholarly journals Elastoplastic Model and Three-Dimensional Method for Unsaturated Soils

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Jinjin Fang ◽  
Yixin Feng
Keyword(s):  
Constitutive Model ◽  
Unsaturated Soils ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Degree Of Saturation ◽  
Triaxial Tests ◽  
Model Parameters ◽  
Elastoplastic Model ◽  
True Triaxial ◽  
Elastoplastic Constitutive Model

This paper proposed a new elastoplastic constitutive model to predict the deformation and strength behaviour of unsaturated soils. Applying the modified Cambridge model as a generalization, the degree of saturation is introduced into the elastoplastic model of unsaturated soil. Under the condition of ensuring that the model parameters are unchanged, the model is transformed into three dimensions based on the SMP criterion transformation stress method. Enhanced modified van Genuchten model under true triaxial conditions is also proposed in this paper to describe hydromechanical behaviours of unsaturated soils. The proposed constitutive model can capture the observed mechanical and hydraulic behaviours. Then, the model is validated via equal p and equal b value true triaxial tests, and the results show that a reasonable agreement can be obtained.

scholarly journals Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 367
Author(s):  
Konstantinos Giannokostas ◽  
Yannis Dimakopoulos ◽  
Andreas Anayiotos ◽  
John Tsamopoulos
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Constitutive Model ◽  
Blood Plasma ◽  
Constitutive Modeling ◽  
Flow Direction ◽  
Momentum Balance ◽  
Plastic Behavior ◽  
Flow Investigation ◽  
The Impact

The present work focuses on the in-silico investigation of the steady-state blood flow in straight microtubes, incorporating advanced constitutive modeling for human blood and blood plasma. The blood constitutive model accounts for the interplay between thixotropy and elasto-visco-plasticity via a scalar variable that describes the level of the local blood structure at any instance. The constitutive model is enhanced by the non-Newtonian modeling of the plasma phase, which features bulk viscoelasticity. Incorporating microcirculation phenomena such as the cell-free layer (CFL) formation or the Fåhraeus and the Fåhraeus-Lindqvist effects is an indispensable part of the blood flow investigation. The coupling between them and the momentum balance is achieved through correlations based on experimental observations. Notably, we propose a new simplified form for the dependence of the apparent viscosity on the hematocrit that predicts the CFL thickness correctly. Our investigation focuses on the impact of the microtube diameter and the pressure-gradient on velocity profiles, normal and shear viscoelastic stresses, and thixotropic properties. We demonstrate the microstructural configuration of blood in steady-state conditions, revealing that blood is highly aggregated in narrow tubes, promoting a flat velocity profile. Additionally, the proper accounting of the CFL thickness shows that for narrow microtubes, the reduction of discharged hematocrit is significant, which in some cases is up to 70%. At high pressure-gradients, the plasmatic proteins in both regions are extended in the flow direction, developing large axial normal stresses, which are more significant in the core region. We also provide normal stress predictions at both the blood/plasma interface (INS) and the tube wall (WNS), which are difficult to measure experimentally. Both decrease with the tube radius; however, they exhibit significant differences in magnitude and type of variation. INS varies linearly from 4.5 to 2 Pa, while WNS exhibits an exponential decrease taking values from 50 mPa to zero.

Assessing the Ergonomic Benefits of a New Adjustable Forklift Backrest

2020 ◽  
Vol 64 (1) ◽  
pp. 976-980
Author(s):  
Pranav Madhav Kuber ◽  
Ehsan Rashedi
Keyword(s):  
Comparative Study ◽  
Motion Capture ◽  
Center Of Pressure ◽  
Body Movement ◽  
Pressure Change ◽  
Motion Capture System ◽  
Design Features ◽  
Wide Range ◽  
Body Sizes ◽  
The Mean

A new forklift backrest has been developed by incorporating adjustability concepts into the design to facilitate comfort to a wide range of users. We have conducted a comparative study between the new and original backrests to assess the effectiveness of design features. Using the phenomenon of restlessness, discomfort of the user was associated with the amount of body movement, where we have used a motion- capture system and a force platform to quantify the individuals’ movement for a wide range of body sizes. Meanwhile, subjective comfort and design feedback were collected using a questionnaire. Our results showed a reduction in the mean torso movement and the maximum center of pressure change of location by 300 and 6 mm, respectively, for the new design. Taking advantage of adjustability feature, the new backrest design exhibited enhanced comfort for longer durations and reduced magnitude of discomfort for a wide range of participants’ body sizes.

scholarly journals Calibration of Finn Model and UBCSAND Model for Simplified Liquefaction Analysis Procedures

2021 ◽  
Vol 11 (11) ◽  
pp. 5283
Author(s):  
Jui-Ching Chou ◽  
Hsueh-Tusng Yang ◽  
Der-Guey Lin
Keyword(s):  
Numerical Simulation ◽  
Constitutive Model ◽  
Structural Damage ◽  
Simulation Analysis ◽  
Constitutive Models ◽  
Soil Liquefaction ◽  
Analysis Procedure ◽  
Liquefaction Resistance ◽  
Simplified Procedure ◽  
Liquefaction Analysis

Soil-liquefaction-related hazards can damage structures or lead to an extensive loss of life and property. Therefore, the stability and safety of structures against soil liquefaction are essential for evaluation in earthquake design. In practice, the simplified liquefaction analysis procedure associated with numerical simulation analysis is the most used approach for evaluating the behavior of structures or the effectiveness of mitigation plans. First, the occurrence of soil liquefaction is evaluated using the simplified procedure. If soil liquefaction occurs, the resulting structural damage or the following mitigation plan is evaluated using the numerical simulation analysis. Rational and comparable evaluation results between the simplified liquefaction analysis procedure and the numerical simulation analysis are achieved by ensuring that the liquefaction constitutive model used in the numerical simulation has a consistent liquefaction resistance with the simplified liquefaction analysis procedure. In this study, two frequently used liquefaction constitutive models (Finn model and UBCSAND model) were calibrated by fitting the liquefaction triggering curves of most used simplified liquefaction analysis procedures (NCEER, HBF, JRA96, and T-Y procedures) in Taiwan via FLAC program. In addition, the responses of two calibrated models were compared and discussed to provide guidelines for selecting an appropriate liquefaction constitutive model in future projects.

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