Modelling the responses of Athabasca oil sand in triaxial compression tests at low pressure

1998 ◽  
Vol 35 (2) ◽  
pp. 395-406 ◽  
Author(s):  
Ahmed M Samieh ◽  
Ron CK Wong
Keyword(s):  
Experimental Data ◽  
Critical State ◽  
Triaxial Compression ◽  
Shear Zones ◽  
Shear Loading ◽  
Compression Tests ◽  
Oil Sand ◽  
Surface Plasticity ◽  
Triaxial Compression Tests ◽  
Disturbance Function

Experimental data from drained triaxial compression tests on Athabasca oil sand at low confining pressures ranging from 50 to 750 kPa are presented. The tested specimens exhibited severe strain-softening with significant dilation but did not approach the critical state entirely by the end of the tests due to the formation of localized shear zones. A homogeneous deformational response in which the entire specimen would reach to the critical state was derived from the experimental response and the critical state parameters. A constitutive model is established to simulate both the experimental and homogeneous deformational responses of Athabasca oil sand. The model is based on describing the evolution of internal microstructural changes with shear loading through a scalar disturbance function. The deformational response of the material is expressed in terms of the responses of its reference states, namely the virgin and fully disturbed states, through the scalar disturbance function. The virgin state of the material is modelled by a generalized single surface plasticity model, whereas the fully disturbed state is assumed to be the critical state. The parameters required to define the model were identified and evaluated. Comparisons between the predicted results and experimental data were made for model performance evaluation.Key words: oil sand, disturbance, plasticity, critical state, shear band.

Mobilized strength components of Athabasca oil sand in triaxial compression

1999 ◽  
Vol 36 (4) ◽  
pp. 718-735 ◽  
Author(s):  
Ron CK Wong
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Shear Banding ◽  
Shear Bands ◽  
Compression Tests ◽  
Oil Sand ◽  
Shear Dilation ◽  
X Ray Imaging ◽  
Microscopy Techniques ◽  
Triaxial Compression Tests

Dense uncemented Athabasca oil sand specimens exhibit unusually high peak strength, dilation with severe softening, and residual strength in drained triaxial compression tests. Computer tomography scanning, X-ray imaging, and scanning electron microscopy techniques are used to examine the microstructural features of the sheared specimens, such as interlocked structure, shear-banding pattern, and porosity distributions inside and outside shear bands. The characteristics of these microstructural features are used to explain the macrodeformation responses observed in the triaxial compression tests. Mobilization of strength components derived from interlocked structure, dilation, rolling, and critical state are analyzed for pre-peak, post-peak softening, and residual states.Key words: oil sand, interlocked structure, shear dilation, shear band, critical state.

scholarly journals The mechanics of subglacial sediment: an example of new “transitional” behaviour

2010 ◽  
Vol 47 (7) ◽  
pp. 775-790 ◽  
Author(s):  
Fatin Altuhafi ◽  
Béatrice A. Baudet ◽  
Peter Sammonds
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Interesting Case ◽  
Strain History ◽  
Compression Tests ◽  
Specimen Density ◽  
The Difference ◽  
Triaxial Compression Tests ◽  
Normal Compression

A series of isotropic compression tests and drained and undrained triaxial compression tests have been performed on glacial sediment from Iceland. Langjökull sediment, which is well graded, is thought to have reached a critical grading during deposition and transportation. Multiple parallel normal compression lines (NCLs) were found, but a unique critical state line (CSL) could be identified. This is unlike other so-called “transitional” soils, whose grading varies between reasonably well graded to gap graded, which tend to have distinct NCLs and critical state lines depending on the specimen density. It is thought that in the case of the Langjökull sediment studied, its particular strain history that involved incessant shearing during deposition accounts for the difference in behaviour. This provides the interesting case of a soil that has been crushed to a critical grading in situ, which depends on the mineralogy of the grains, which was then sampled and tested. Despite the unique grading, samples with a range of different void ratios can be prepared and the combination of grading and density seems to set a fabric that cannot be changed by compression, resulting in multiple parallel NCLs. At the critical state, however, the fabric has been destroyed and the CSL is unique.

Undrained triaxial strength and stress–strain characteristics of a glacial till soil

1988 ◽  
Vol 25 (3) ◽  
pp. 428-439 ◽  
Author(s):  
J. H. Atkinson ◽  
J. A. Little
Keyword(s):  
Critical State ◽  
Soil Mechanics ◽  
Triaxial Compression ◽  
Practical Importance ◽  
Small Strain ◽  
Compression Tests ◽  
Triaxial Strength ◽  
Current State ◽  
Boulder Clay ◽  
Triaxial Compression Tests

Undrained triaxial compression tests were carried out on reconstituted and nominally undisturbed tubed samples of a lodgement till from the Vale of St. Albans in Hertfordshire, England. The soil is a matrix-dominant, chalky boulder clay of Anglian age with little discernable engineering fabric. Electron microscope observations showed the presence of crystalline calcite in tube samples.The test results were examined within the general framework of critical state soil mechanics using normalizing procedures to take account of the different states and stress histories of the samples. These analyses demonstrate the practical importance of accounting for the current state and stress history in the interpretation of soil test data.The present results form a self-consistent pattern of behaviour. Differences between reconstituted and tubed samples were found only at small strain and may be attributed to cementing in tubed samples, which is broken down during reconstitution and during relatively large straining in recompression and shearing. Key words: boulder clay, cemented soil, critical state, shear strength, soil mechanics, stiffness, till, triaxial test.

scholarly journals Triaxial compression behavior of 3D printed and natural sands

2021 ◽  
Vol 23 (4) ◽  
Author(s):  
Sheikh Sharif Ahmed ◽  
Alejandro Martinez
Keyword(s):  
3D Printing ◽  
Critical State ◽  
Mechanical Response ◽  
Triaxial Compression ◽  
Coarse Grained ◽  
Compression Tests ◽  
Natural Sand ◽  
Compression Behavior ◽  
3D Printed ◽  
Triaxial Compression Tests

AbstractDifferent particle properties, such as shape, size, surface roughness, and constituent material stiffness, affect the mechanical behavior of coarse-grained soils. Systematic investigation of the individual effects of these properties requires careful control over other properties, which is a pervasive challenge in investigations with natural soils. The rapid advance of 3D printing technology provides the ability to produce analog particles with independent control over particle size and shape. This study examines the triaxial compression behavior of specimens of 3D printed sand particles and compares it to that of natural sand specimens. Drained and undrained isotropically-consolidated triaxial compression tests were performed on specimens composed of angular and rounded 3D printed and natural sands. The test results indicate that the 3D printed sands exhibit stress-dilatancy behavior that follows well-established flow rules, the angular 3D printed sand mobilizes greater critical state friction angle than that of rounded 3D printed sand, and analogous drained and undrained stress paths can be followed by 3D printed and natural sands with similar initial void ratios if the cell pressure is scaled. The results suggest that some of the fundamental behaviors of soils can be captured with 3D printed soils, and that the interpretation of their mechanical response can be captured with the critical state soil mechanics framework. However, important differences in response arise from the 3D printing process and the smaller stiffness of the printed polymeric material. Graphic abstract Artificial sand analogs were 3D printed from X-ray CT scans of sub-rounded and sub-angular natural sands. Triaxial compression tests were performed to characterize the strength and dilatancy behavior as well as critical staste parameters of the 3D printed sands and to compare it to that exhibited by the natural sands.

A Simple Unconsolidated Undrained Triaxial Compression Test Emulator

2015 ◽  
Vol 771 ◽  
pp. 104-107
Author(s):  
Riska Ekawita ◽  
Hasbullah Nawir ◽  
Suprijadi ◽  
Khairurrijal
Keyword(s):  
Triaxial Compression ◽  
Measurement Data ◽  
Radial Strain ◽  
Compression Tests ◽  
Viscous Effects ◽  
Axial Pressure ◽  
Strain Stress ◽  
The University ◽  
And Storage ◽  
Triaxial Compression Tests

An unconsolidated undrained (UU) test is one type of triaxial compression tests based on the nature of loading and drainage conditions. In order to imitate the UU triaxial compression tests, a UU triaxial emulator with a graphical user interface (GUI) was developed. It has 5 deformation sensors (4 radial deformations and one vertical deformation) and one axial pressure sensor. In addition, other inputs of the emulator are the cell pressure, the height of sample, and the diameter of sample, which are provided by the user. The emulator also facilitates the analysis and storage of measurement data. Deformation data fed to the emulator were obtained from real measurements [H. Nawir, Viscous effects on yielding characteristics of sand in triaxial compression, Dissertation, Civil Eng. Dept., The University of Tokyo, 2002]. Using the measurement data, the stress vs radial strain, stress vs vertical strain, and Mohr-Coulomb circle curves were obtained and displayed by the emulator.

Strength envelope of granular soil stabilized by multi-axial geogrid in large triaxial tests

2020 ◽  
Vol 57 (3) ◽  
pp. 448-452 ◽  
Author(s):  
A.S. Lees ◽  
J. Clausen
Keyword(s):  
Triaxial Compression ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Failure Envelope ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Triaxial Compression Tests ◽  
Properties Of Soil

Conventional methods of characterizing the mechanical properties of soil and geogrid separately are not suited to multi-axial stabilizing geogrid that depends critically on the interaction between soil particles and geogrid. This has been overcome by testing the soil and geogrid product together as one composite material in large specimen triaxial compression tests and fitting a nonlinear failure envelope to the peak failure states. As such, the performance of stabilizing, multi-axial geogrid can be characterized in a measurable way. The failure envelope was adopted in a linear elastic – perfectly plastic constitutive model and implemented into finite element analysis, incorporating a linear variation of enhanced strength with distance from the geogrid plane. This was shown to produce reasonably accurate simulations of triaxial compression tests of both stabilized and nonstabilized specimens at all the confining stresses tested with one set of input parameters for the failure envelope and its variation with distance from the geogrid plane.

scholarly journals Semi-empirical elastic–thermoviscoplastic model for clay

2016 ◽  
Vol 53 (10) ◽  
pp. 1583-1599 ◽  
Author(s):  
David Kurz ◽  
Jitendra Sharma ◽  
Marolo Alfaro ◽  
Jim Graham
Keyword(s):  
Stress Level ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Compression Tests ◽  
One Dimensional ◽  
Load Duration ◽  
Compression Creep ◽  
Overconsolidated Clays ◽  
Semi Empirical ◽  
Triaxial Compression Tests

Clays exhibit creep in compression and shear. In one-dimensional compression, creep is commonly known as “secondary compression” even though it is also a significant component of deformations resulting from shear straining. It reflects viscous behaviour in clays and therefore depends on load duration, stress level, the ratio of shear stress to compression stress, strain rate, and temperature. Research described in the paper partitions strains into elastic (recoverable) and plastic (nonrecoverable) components. The plastic component includes viscous strains defined by a creep rate coefficient ψ that varies with plasticity index and temperature (T), but not with stress level or overconsolidation ratio (OCR). Earlier elastic–viscoplastic (EVP) models have been modified so that ψ = ψ(T) in a new elastic–thermoviscoplastic (ETVP) model. The paper provides a sensitivity analysis of simulated results from undrained (CIŪ) triaxial compression tests for normally consolidated and lightly overconsolidated clays. Axial strain rates range from 0.15%/day to 15%/day, and temperatures from 28 to 100 °C.

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