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.

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.

The effect of tamping conditions and sample preparation on undrained shear strengths of a non-plastic sandy silt tailings

2021 ◽  
Author(s):  
David Reid ◽  
Riccardo Fanni ◽  
Peter DiDonna
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Engineering Practice ◽  
Compression Tests ◽  
In Situ Testing ◽  
Sandy Silt ◽  
Direct Simple Shear ◽  
Lead Zinc ◽  
Increased Strength

A series of direct simple shear (DSS) tests were carried out on a non-plastic sandy silt lead-zinc-silver tailings to develop a relationship between undrained shearing behaviour and density, where in situ testing had identified contractive behaviour. The critical state line was also obtained through triaxial compression tests to enable the DSS tests to be viewed in a critical state framework and allow comparison with in situ testing. It was found that the gravimetric water content (GWC) used to tamp the specimens had a significant effect on the resulting undrained strengths when attempting to achieve dense states - with higher GWC giving lower strength at a given density than a lower GWC. Intact and slurry deposited (SD) samples were also tested to access denser states without inducing tamping-related stresses. These showed a more consistent trend with the loose-tamped specimens, and with other data from the literature. Plausible explanations as to the causes of the increased strength of dense-tamped samples were obtained through estimating potential preconsolidation stresses and “locked in” horizontal stresses that may occur from dense tamping. The importance of these observations on the development of density - strength profiles in engineering practice was outlined.

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.

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.

A Comparative Study of Hydromechanical Properties in Saturated and Partially Saturated Conditions of Two Soils from the Runway of Oran Airport

2017 ◽  
Vol 21 ◽  
pp. 319-326
Author(s):  
Mohamed Chikhaoui ◽  
Dashnor Hoxha ◽  
Naima Belayachi ◽  
Ammar Nechnech
Keyword(s):  
Triaxial Compression ◽  
Confining Pressure ◽  
Natural Soil ◽  
Compression Tests ◽  
Partially Saturated ◽  
Laboratory Results ◽  
Pressure Meter ◽  
Statistical Representativeness ◽  
Triaxial Compression Tests

This study concerns the ground soils of the second runway of the Es-Sénia airport in Oran (Algeria). This airport was built on a very complex hydro geotechnical site when underground cavities, following the dissolution of gypsum soil, were found during the before-construction geologic studies. Several, techniques are used in laboratory (Permeability, triaxial compression tests at various confining pressure, and hydric tests in saturated and unsaturated conditions) and for in situ it’s used the results of SPT and pressure-meter tests. A comparison of parameters of two soils identified in saturated and partially saturated conditions by in situ and laboratory tests was performed in order to respond to questions of the similarity of hydro mechanical properties of two soils as well as their statistical representativeness of the in-situ reality. It is found that, in respect to the studied parameters, laboratory results are statistically significant and reconstituted soils is statistically representative of natural soil reconstitution.

scholarly journals Porosity and Permeability Evolution with Deviatoric Stress of Reservoir Sandstone: Insights from Triaxial Compression Tests and In Situ Compression CT

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Cong Hu ◽  
Franck Agostini ◽  
Yonggang Jia
Keyword(s):  
Triaxial Compression ◽  
Deviatoric Stress ◽  
Permeability Evolution ◽  
Compression Tests ◽  
Confining Stress ◽  
Porosity Reduction ◽  
Porosity And Permeability ◽  
Deviatoric Stresses ◽  
Triaxial Compression Tests

Porosity and permeability are the two most important characteristics of underground gas storage in sandstone reservoirs. Injection of gas into reservoir rocks will cause rock deformation. The deformation will influence the porosity and permeability properties of the rocks. We investigate the evolution of these two properties of storage sandstone by triaxial compression tests and a uniaxial in situ compression CT test. As the deviatoric stress increases, the sandstone is compressed firstly (porosity reduction) and then dilates (porosity enhancement). With the increase in confining stress, the occurrence of volumetric dilation will be delayed. Trapped porosity of this sandstone at different deviatoric stresses is very small (0.122%-0.115%) which indicates that nearly all pores are connected. During the compression stage, the decrease in permeability is related to compression of pores and microcracks. During the volumetric dilation stage, it is related to increase in tortuosity. This interpretation can be confirmed by observations of in situ compression CT. The permeability evolution estimated by pore network modeling is consistent with macroscopic testing results.

scholarly journals Evaluation of Failure Behavior and Strength of Fractured Rock Sample Using In Situ Triaxial Compression Tests and Expanded Distinct Element Method

2010 ◽  
Vol 452-453 ◽  
pp. 225-228
Author(s):  
B. Li ◽  
Y. Jiang
Keyword(s):  
Rock Sample ◽  
Fractured Rock ◽  
Distinct Element ◽  
Triaxial Compression ◽  
Peak Stress ◽  
Failure Behavior ◽  
Compression Tests ◽  
In Situ Tests ◽  
Triaxial Compression Tests

The in-situ tests have been widely used to directly assess the strength and deformability of rock mass, along with which, various numerical approaches were proposed to give rational interpretations to the mechanical phenomenon happening during these tests. In this study, the so-called potential cracks are introduced into DEM model, leading to expanded DEM (EDEM) approach which is capable of simulating the cracking in intact rocks. The EDEM is applied to an in-situ triaixal compression test on a fractured rock sample. The simulation has well represented the failure mode, peak stress and elastic modulus obtained from tests as well as the cracking phenomenon and the slips on fracture planes during the loading process.

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.

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