The behaviour of very loose sand in the triaxial compression test

1989 ◽  
Vol 26 (1) ◽  
pp. 103-113 ◽  
Author(s):  
J. A. Sladen ◽  
J. M. Oswell
Keyword(s):  
Cyclic Loading ◽  
Critical State ◽  
Strain Softening ◽  
Soil Mechanics ◽  
Triaxial Compression ◽  
State Testing ◽  
Loose Sand ◽  
Sand Liquefaction ◽  
Strain Behaviour ◽  
First Time

Very loose sand is defined as sand whose state is significantly looser than its critical state. The detailed stress-strain behaviour of very loose sand in triaxial compression is described for the first time within the framework of critical state soil mechanics. It is shown that the undrained behaviour of very loose sand under static loading can be rationalized by normalization with respect to the critical state, an approach that has been successful when applied to clays and to sands dense of critical. Strain contours in normalized stress space are presented for several sands and are shown to be remarkably consistent. The observed normalized behaviour is used to develop a simple constitutive model for the behaviour of very loose sands, based on plasticity theory. It is demonstrated that this model can be used successfully to predict the essential features of the behaviour of very loose sands in undrained and drained triaxial compression including cyclic loading conditions. The model includes the strain softening that occurs in very loose sands in conditions of impeded drainage and the cumulative increase in pore pressure that occurs during undrained cyclic loading. It can be used to predict the onset of liquefaction, a phenomenon only exhibited by very loose sands and quick clays. Key words: sand, liquefaction, triaxial test, cyclic loading, steady state testing, collapse surface.

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.

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.

Influences of initial anisotropy and principal stress rotation on the undrained monotonic behavior of a loose silica sand

2021 ◽  
Author(s):  
Kazem Fakharian ◽  
Farzad Kaviani-Hamedani ◽  
S M Reza Imam
Keyword(s):  
Phase Transformation ◽  
Critical State ◽  
Soil Mechanics ◽  
Triaxial Compression ◽  
Silica Sand ◽  
Bender Element ◽  
Cyclic Shear ◽  
Stress Rotation ◽  
Initial Anisotropy ◽  
Stress Ratios

Triaxial compression and extension tests have been conducted under different initial anisotropy conditions to investigate the undrained response of a crushed silica sand. The loose to medium specimens were prepared using the moist tamping method. Five stress paths with different stress ratios (q/p^') were employed to prepare anisotropically consolidated specimens. Several specimens were consolidated under a specific condition in which a stress rotation occurred under undrained monotonic shearing similar to a reversed cyclic shear stress loading during an earthquake. The effects of initial induced anisotropy at consolidation on the onset of liquefaction, phase transformation, and critical state are investigated within the framework of Anisotropic Critical State Soil Mechanics (ACSSM). In addition, fabric evolution during shearing towards the critical state is evaluated using bidirectional bender element tests. The results illustrate the fact that there is a unique anisotropic critical state representing anisotropic fabric, irrespective of initial anisotropy, and the states of stress. Similar to the critical state line, the phase transformation line has the same loci for different initial anisotropies.

Influence of fines on the collapse of loose sands

1994 ◽  
Vol 31 (5) ◽  
pp. 728-739 ◽  
Author(s):  
T.D. Pitman ◽  
P.K. Robertson ◽  
D.C. Sego
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Strain Softening ◽  
Triaxial Compression ◽  
Fine Sand ◽  
Large Strains ◽  
Loose Sand ◽  
Test Program ◽  
Softening Behaviour ◽  
Scanning Electron

A study has been carried out to investigate the influence of fines and gradation on the skeletal collapse behaviour of loosely prepared sand samples. Loose sand samples, formed by moist tamping and consolidated to the same effective stress level, were prepared with varying percentages of both plastic and non-plastic fines (< 74 μm) and non-plastic fine sand (> 74 μm). Samples were isotropically consolidated and subjected to monotonic undrained triaxial compression. Results indicate that increased percentages of fines (< 74 μm) have a pronounced effect on the monotonic undrained behaviour at large strains (> 0.5%). This change is represented by a decreased strain softening behaviour and a shifting of the steady-state line. Variation of the gradation of the host sand appears to have little effect on the monotonic undrained behaviour. A supplemental study, involving use of the scanning electron microscope, was carried out to evaluate the findings of the test program in terms of sand fabric. Key words : collapse, monotonic undrained behaviour, scanning electron microscope, fabric.

Effects of fines on liquefaction behaviour in well-graded materials

2017 ◽  
Vol 54 (10) ◽  
pp. 1460-1471 ◽  
Author(s):  
Katherine A. Kwa ◽  
David W. Airey
Keyword(s):  
Critical State ◽  
Soil Mechanics ◽  
State Parameter ◽  
Triaxial Tests ◽  
Particle Sizes ◽  
Graded Materials ◽  
Fines Content ◽  
Cyclic Resistance ◽  
Wide Range ◽  
Soil Behaviour

This study uses a critical state soil mechanics perspective to understand the mechanics behind the liquefaction of metallic ores during transport by ship. These metallic ores are transported at relatively low densities and have variable gradings containing a wide range of particle sizes and fines contents. The effect of the fines content on the location of the critical state line (CSL) and the cyclic liquefaction behaviour of well-graded materials was investigated by performing saturated, standard drained and undrained monotonic and compression-only cyclic triaxial tests. Samples were prepared at four different gradings containing particle sizes from 9.5 mm to 2 μm with fines (<75 μm) contents of 18%, 28%, 40%, and 60%. In the e versus log[Formula: see text] plane, where e is void ratio and [Formula: see text] is mean effective stress, the CSLs shifted upwards approximately parallel to one another as the fines content was increased. Transitional soil behaviour was observed in samples containing 28%, 40%, and 60% fines. A sample’s cyclic resistance to liquefaction depended on a combination of its density and state parameter, which were both related to the fines content. Samples with the same densities were more resistant to cyclic failure if they contained higher fines contents. The state parameter provided a useful prediction for general behavioural trends of all fines contents studied.

A New Nonlinear Stress-Strain Model for Soils at Various Strain Levels

2013 ◽  
Vol 631-632 ◽  
pp. 782-788
Author(s):  
Cheng Chen ◽  
Zheng Ming Zhou
Keyword(s):  
Compression Test ◽  
Triaxial Compression ◽  
Small Strain ◽  
Empirical Formulas ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Proposed Model ◽  
Nonlinear Stress ◽  
London Clay ◽  
Strain Model

Soils have nonlinear stiffness and develops irrecoverable strains even at very small strain levels. Accurate modeling of stress-strain behaviour at various strain levels is very important for predicting the deformation of soils. Some existing stress-strain models are reviewed and evaluated firstly. And then a new simple non-linear stress-strain model is proposed. Four undetermined parameters involved in the proposed model can be obtained through maximum Young’s module, deformation module, and limit deviator stress and linearity index of soils that can be measured from experiment directly or calculated by empirical formulas indirectly. The effectiveness of the proposed stress-strain model is examined by predicting stress-strain curves measured in plane-strain compression test on Toyota sand and undrained triaxial compression test on London clay. The fitting results of the proposed model are in good agreement with experimental data, which verify the effectiveness of the model.

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