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.

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.

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.

scholarly journals Experimental Study on the Shear Band of Methane Hydrate-Bearing Sediment

2021 ◽  
Vol 9 (11) ◽  
pp. 1158
Author(s):  
Xiaobing Lu ◽  
Xuhui Zhang ◽  
Fangfang Sun ◽  
Shuyun Wang ◽  
Lele Liu ◽  
...  
Keyword(s):  
Shear Band ◽  
Gas Hydrate ◽  
Methane Hydrate ◽  
Triaxial Compression ◽  
Shear Banding ◽  
Oblique Line ◽  
Shear Bands ◽  
Compression Tests ◽  
Computer Tomography Scan ◽  
Hydrate Saturation

The occurrence of a shear band is often thought as the precursor of failure. To study the initiation of shear banding in gas hydrate-bearing sediments, two groups of triaxial compression tests combined with a CT (computer tomography) scan were conducted by triaxial CT-integrated equipment under two confining pressures and seven hydrate saturations. The macro stress–strain curves and the corresponding CT scanning images of the micro-structure and the distribution of the components were obtained. The geometric parameters of the shear bands were measured based on the CT images at four typical axial strains, respectively. The distribution characteristics of soil particles, water, hydrate and gas were also analyzed. It is shown that the existence of methane hydrate changes the mechanical property of hydrate-bearing sediment from plastic failure to brittle failure when the hydrate saturation is over 13%, which occurs in the range of the tests in this paper. The peak of the deviatoric stress increases with the hydrate saturation. The shear band is in either a single oblique line or inter-cross lines depending on the hydrate saturation, the effective confining pressure and the initial distribution of the gas hydrate. Most of the shear band surfaces are not straight, and the widths of the shear bands are almost non-uniformly distributed.

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 Effect of Compaction Banding on the Hydraulic Properties of Porous Rock: Part I—Experimental Investigation

2021 ◽  
Author(s):  
Julia Leuthold ◽  
Eleni Gerolymatou ◽  
Maximiliano R. Vergara ◽  
Theodoros Triantafyllidis
Keyword(s):  
Hydraulic Properties ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Shear Bands ◽  
Experimental Investigations ◽  
Porous Rocks ◽  
Compression Tests ◽  
Compaction Bands ◽  
Maximum Permeability ◽  
Triaxial Compression Tests

AbstractThe mechanical behavior and the influence of compaction banding on the hydraulic properties in soft porous rocks were studied. The tested rock was Calcarenite Tuffeau de Maastricht. In the frame of experimental investigations, triaxial and oedometric tests were conducted under dry and drained conditions. The results demonstrated that the rock is forming discrete compaction bands under high confining stresses and steep angle shear bands under low confining stresses. Permeability measurements during the oedometric and triaxial compression tests under drained conditions demonstrated that the axial permeability decreases with increasing axial strain. The maximum permeability decrease was three orders of magnitude for 40% of axial strain.

scholarly journals Evaluation of Shear Dilation Capability/Potential and Permeability Changes in Karamay Oil Sands under Water Injection

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-21 ◽  
Author(s):  
Yanfang Gao ◽  
Huiwen Pang ◽  
Yan Jin ◽  
Mian Chen
Keyword(s):  
Oil Sands ◽  
Triaxial Compression ◽  
Water Injection ◽  
Theoretical Models ◽  
Oil Field ◽  
Particle Packing ◽  
Compression Tests ◽  
Oil Sand ◽  
Shear Dilation ◽  
Porosity And Permeability

Water injection can effectively improve the reservoir porosity and permeability by shear dilation in the vicinity of wellbores. In this paper, shear dilation and permeability improvement capability/potential are proposed to describe the evolutions of porosity and permeability under water injection-induced shear. The mathematical models based on Karamay oil sand microstructures derived from ESEM (environmental scanning electron microscope) are established to predict the shear dilation effects based on the particle packing theory. Triaxial compression and permeability experiments are conducted to validate the theoretical models, and the experimental data is consistent with model results. Also, the study compares shear dilation capabilities evaluated from three scales: ESEM (μm), laboratory triaxial compression tests (cm), and field injection tests (m). Major conclusions through an application on the wellpair A-2 in area A of the Karamay oil field showed that the oil sands have an excellent shear dilation potential. The larger arrangement angle results in stronger shear dilation and permeability, which means a lower arrangement angle provides a higher potential for improvement. The shear dilation capabilities predicted by ESEM, triaxial compression experiments, and field injection data descend in turn, which indicates that the actual shear dilation capability is difficult to be utilized by present field operations.

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.

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