scholarly journals Constitutive model describing the hydro-mechanical behaviors of compacted bentonite clay based on the crystal surface phenomena

2020 ◽  
Vol 205 ◽  
pp. 04012
Author(s):  
Hiroyuki Kyokawa
Keyword(s):  
Constitutive Model ◽  
Crystal Surface ◽  
Expansive Soil ◽  
Bentonite Clay ◽  
Degree Of Saturation ◽  
Type Model ◽  
Inelastic Behavior ◽  
Surface Phenomena ◽  
Compacted Bentonite ◽  
Soil Skeleton

A constitutive model for unsaturated expansive soil based on the crystal surface phenomena is proposed. The behavior of the proposed model is described as a double structure, with the soil skeleton and the interlaminar behaviors. The soil skeleton behavior is modeled by the Cam clay type model based on the Bishop’s effective stress, which can consider the degree of saturation-induced hardening and inelastic behavior in the over-consolidated region and is capable of describing hydraulic collapse. On the other hand, the interlaminar behavior is give as a result of the interlaminar equilibrium of clay minerals. The diffusion double layer repulsive force in the interlaminar equilibrium varies with the degree of saturation, and it mainly causes the hydraulic swelling of expansive soil. The performance of the model is validated through the simulations of the suction-controlled oedometer tests on the heavily compacted bentonite.

Two-time-scales and time-averaging approaches for the analysis of cyclic creep based on Armstrong–Frederick type constitutive model

2018 ◽  
Vol 233 (5) ◽  
pp. 1690-1700 ◽  
Author(s):  
Holm Altenbach ◽  
Dmitry Breslavsky ◽  
Konstantin Naumenko ◽  
Oksana Tatarinova
Keyword(s):  
Cyclic Loading ◽  
Constitutive Model ◽  
Inelastic Strain ◽  
Cyclic Creep ◽  
Analytical Form ◽  
Type Model ◽  
Time Averaging ◽  
Inelastic Behavior ◽  
Time Step ◽  
The Mean

The aim of this paper is the analysis of inelastic behavior under periodic cyclic loading regimes for materials showing recovery effects. Starting with the Armstrong–Frederick type model and applying the two-time-scale asymptotic technique, the constitutive equation for the mean inelastic strain rate and the evolution equation for the mean backstress variable are derived. The advantage of the presented technique is the closed analytical form of the solutions such that the influence of the loading profiles on the resulting slow cycle-by-cycle strain accumulation can be analyzed explicitly. To validate the derived equations, the original constitutive model is integrated numerically by applying the time-step procedure for various cyclic loading profiles. Numerical examples are presented to illustrate cyclic creep behavior of X20CrMoV12-1 heat resistant steel.

scholarly journals A Characterization for the Hot Flow Behaviors of As-extruded 7050 Aluminum Alloy

2015 ◽  
Vol 34 (7) ◽  
pp. 643-650
Author(s):  
Guo-zheng Quan ◽  
Jin Liu ◽  
An Mao ◽  
Bo Liu ◽  
Jin-sheng Zhang
Keyword(s):  
Aluminum Alloy ◽  
Constitutive Model ◽  
Work Hardening ◽  
True Strain ◽  
Deep Understanding ◽  
Type Model ◽  
Compression Tests ◽  
Average Absolute Relative Error ◽  
7050 Aluminum Alloy ◽  
Peak Value

Abstract The deep understanding of flow behaviors of as-extruded 7050 aluminum alloy significantly contributes to the accuracy simulation for its various plastic forming processes. In order to obtain the improved Arrhenius-type equation with variable parameters for this alloy, a series of compression tests were performed at temperatures of 573 K, 623 K, 673 K, 723 K and strain rates of 0.01 s−1, 0.1 s−1, 1 s−1, 10 s−1 with a height reduction of 60% on Gleeble-1500 thermo-mechanical simulator. It is obvious that strain rate, strain and temperature all have a significant effect on the hot flow behaviors, and the true stress–true strain curves indicate three types after the peak value: decreasing gradually to a steady state with sustaining DRX softening till a balance with work hardening, decreasing continuously with sustaining increasing DRX softening beyond work hardening and maintaining higher stress level after the peak value with a balance between work hardening and DRV softening. Based on the experimental data, the improved Arrhenius-type constitutive model was established to predict the high temperature flow stress of as-extruded 7050 aluminum alloy. The accuracy and reliability of the improved Arrhenius-type model were further evaluated in terms of the correlation coefficient (R), here 0.98428, the average absolute relative error (AARE), here 3.5%. The results indicate that the improved Arrhenius-type constitutive model presents a good predictable ability.

Some Aspects on the Use of Iron Canisters for HLW

1985 ◽  
Vol 50 ◽  
Author(s):  
Ivars Neretnieks
Keyword(s):  
Bentonite Clay ◽  
Potential Effect ◽  
Hydrogen Gas ◽  
Lithostatic Pressure ◽  
Equilibrium Pressure ◽  
Capillary Suction ◽  
Compacted Bentonite ◽  
High Level Nuclear Waste ◽  
High Level ◽  
Rock Overburden

AbstractIron canisters for high level nuclear waste embedded in compacted bentonite in deep geologic repositories will corrode forming hydrogen gas. The equilibrium pressure (when corrosion would stop) has been estimated to be between 500 and 1000 atm. under repository conditions. As this is much higher than the lithostatic pressure (weight of rock overburden) the gas must be allowed to escape before it disrupts the repository. Escape by diffusion alone is not sufficient but recent experiments have demonstrated that the larger pores in the bentonite are blown free of water and let the gas escape before excessive pressures build up.The potential effect of a capillary breaking layer (CBL) has been explored. A fine layer nearest the canister (e.q. quartz sand) would have much lower capillary suction pressures than the bentonite clay and would keep the water out as long as there is sufficient overpressure. As long as the CBL is void of liquid water no radionuclides can escape, even if the canister is penetrated.

Viscoplastic constitutive approach for rate-sensitive structured clays

2009 ◽  
Vol 46 (6) ◽  
pp. 609-626 ◽  
Author(s):  
Sean D. Hinchberger ◽  
Guangfeng Qu
Keyword(s):  
Constitutive Model ◽  
Term Structure ◽  
Triaxial Compression ◽  
State Theory ◽  
Clay Particles ◽  
Hardening Law ◽  
State Dependent ◽  
Structured Clay ◽  
Soil Skeleton ◽  
Dependent Viscosity

This paper extends an existing elastic–viscoplastic (EVP) constitutive model using a state-dependent viscosity parameter to describe the engineering response of undisturbed structured clay. The term structure refers to the effects of fabric and weak cementation bonds between clay particles. The extended constitutive model is coupled with the Biot consolidation theory and is formulated to describe the intrinsic or unstructured response of clay using overstress viscoplasticity, an elliptical cap yield surface, Drucker–Prager failure envelope, and a hardening law from critical state theory. The clay structure is mathematically accounted for by assuming that the initial fluidity of structured clay at yield and failure is very low and that the fluidity increases with increasing plastic strain. This process is usually referred to as “destructuration.” The formulation is evaluated using Saint-Jean-Vianney (SJV) clay by comparing calculated and measured behaviour during consolidated isotropically undrained triaxial compression, triaxial creep, and constant rate-of-strain Ko′-consolidation tests. The comparisons indicate that the EVP constitutive model can describe most of the rate-sensitive behaviour of SJV clay during both drained and undrained laboratory tests involving either constant-volume shear or predominantly volumetric compression of the soil skeleton.

Diffusion of 22Na+, 85Sr2+, 134Cs+ and 57Co2+ in bentonite clay compacted to different densities: experiments and modeling

2002 ◽  
Vol 90 (9-11) ◽  
Author(s):  
M. Molera ◽  
T. Eriksen
Keyword(s):  
Porous Media ◽  
Pore Water ◽  
Water System ◽  
Bentonite Clay ◽  
Saturated Porous Media ◽  
Diffusion Study ◽  
Clay Surface ◽  
Compacted Bentonite ◽  
Water Saturated ◽  
Sorption Mechanisms

SummaryThe diffusion of radionuclides in water-saturated porous media, such as compacted bentonite, is traditionally modeled assuming diffusion in the pore water and immobilization by adsorption on the clay surface. In reality there are several sorption mechanisms acting in the clay-water system. We have therefore carried out a careful diffusion study of the cations Na

scholarly journals Numerical Simulation Of The Treatment Of Soil Swelling Using Grid Geocell Columns

2015 ◽  
Vol 23 (2) ◽  
pp. 9-18 ◽  
Author(s):  
Mohammed Y. Fattah ◽  
Raid R. Al-Omari ◽  
Haifaa A. Ali
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Expansive Soil ◽  
Matric Suction ◽  
Degree Of Saturation ◽  
Axial Forces ◽  
Column Material ◽  
Cap Model

Abstract In this paper, a method for the treatment of the swelling of expansive soil is numerically simulated. The method is simply based on the embedment of a geogrid (or a geomesh) in the soil. The geogrid is extended continuously inside the volume of the soil where the swell is needed to be controlled and orientated towards the direction of the swell. Soils with different swelling potentials are employed: bentonite base-Na and bentonite base-Ca samples in addition to kaolinite mixed with bentonite. A numerical analysis was carried out by the finite element method to study the swelling soil's behavior and investigate the distribution of the stresses and pore water pressures around the geocells beneath the shallow footings. The ABAQUS computer program was used as a finite element tool, and the soil is represented by the modified Drucker-Prager/cap model. The geogrid surrounding the geocell is assumed to be a linear elastic material throughout the analysis. The soil properties used in the modeling were experimentally obtained. It is concluded that the degree of saturation and the matric suction (the negative pore water pressure) decrease as the angle of friction of the geocell column material increases due to the activity of the sand fill in the dissipation of the pore water pressure and the acceleration of the drainage through its function as a drain. When the plasticity index and the active depth (the active zone is considered to be equal to the overall depth of the clay model) increase, the axial movement (swelling movement) and matric suction, as a result of the increase in the axial forces, vary between this maximum value at the top of the layer and the minimum value in the last third of the active depth and then return to a consolidation at the end of the depth layer.

scholarly journals Numerical Analysis of Test Embankment on Soft Ground Using Multi-Laminate Type Model with Destructuration / Analiza Numeryczna Nasypu Drogowego Posadowionego Na Gruncie Słabonosnym Z Zastosowaniem Modelu Wielopłaszczyznowego Z Destrukturyzacja

2011 ◽  
Vol 57 (1) ◽  
pp. 27-44
Author(s):  
M. Cundi
Keyword(s):  
Constitutive Model ◽  
Constitutive Models ◽  
In Situ Stress ◽  
Type Model ◽  
Model Parameters ◽  
Structural Anisotropy ◽  
Soft Clays ◽  
Stress Induced Anisotropy ◽  
Test Embankment

Abstract A multi-laminate constitutive model for soft soils incorporating structural anisotropy is presented. Stress induced anisotropy of strength, which is present in multi-laminate type constitutive models, is augmented by directionally distributed overconsolidation. The model is presented in the elastic-plastic version in order to simulate strength anisotropy of soft clayey soils and destructuration effects. Performance of the model is shown for some element tests and for the numerical simulation of a trial road embankment constructed on soft clays at Haarajoki, Finland. The numerical calculations are completed with the commercial finite element code capable to perform coupled static/consolidation analysis of soils. Problems related to the initiation of in situ stress state, conditions of preconsolidation, as well as difficulties linked to estimation of the model parameters are discussed. Despite simple assumptions concerning field conditions and non-viscous formulation of the constitutive model, the obtained final results are of a sufficient accuracy for geotechnical practice.

Sign in / Sign up

Export Citation Format

Share Document