scholarly journals Reconsideration of the State Boundary Surface Based on Areal Strain.

2002 ◽  
pp. 69-78 ◽  
Author(s):  
Fumihiko FUKUDA ◽  
Toshiyuki MITACHI ◽  
Satoru SHIBUYA
Keyword(s):  
Boundary Surface ◽  
The State ◽  
State Boundary ◽  
State Boundary Surface

The effect of anisotropic elasticity on the yielding characteristics of overconsolidated natural clay

2001 ◽  
Vol 38 (1) ◽  
pp. 125-137 ◽  
Author(s):  
Vinayagamoorthy Sivakumar ◽  
Isaac Gregg Doran ◽  
Jim Graham ◽  
Arvee Johnson
Keyword(s):  
Boundary Surface ◽  
Anisotropic Elasticity ◽  
The State ◽  
Natural Clay ◽  
Natural Soils ◽  
State Boundary ◽  
Yield Loci ◽  
Anisotropic Elastic ◽  
Good Agreement ◽  
State Boundary Surface

Quantitative application of elastoplastic theory to the yielding behaviour of natural soils has always been uncertain. Part of the reason is that the theory was developed for reconstituted materials with isotropic structure, in contrast to natural soils that are usually anisotropic. The approach considered in this study assumes that pre-yielding behaviour is governed by the theory of linear anisotropic elasticity and that yield loci in the mean effective stress ( p') – deviator stress (q) plane are aligned approximately along the coefficient of earth pressure (K0) line. The assumption of a rotated yield locus associated with anisotropic elastic behaviour within the state boundary surface indicates that the elastic wall within the state boundary surface is inclined. The form of the state boundary surface has been determined mathematically in terms of anisotropic elastic and Cam-Clay soil parameters. Stress path tests were conducted on samples of Belfast Upper Boulder Clay removed from a depth of 28 m below ground surface. Good agreement was found between predicted and measured yield loci. The study also examined the influence of subsequent isotropic compression on the yielding characteristics of the natural clay. The indications are that the anisotropy developed during deposition disappears when the sample is loaded to a stress level at least twice the stress generated during the original deposition process. The methods developed in the paper have also been applied to test results reported previously on Winnipeg clay, and good agreement was obtained.Key words: sampling, anisotropy, elasticity, suction, stiffness, yielding.

State-boundary surface for very loose sand and its practical implications

1994 ◽  
Vol 31 (3) ◽  
pp. 321-334 ◽  
Author(s):  
S. Sasitharan ◽  
P. K. Robertson ◽  
D. C. Sego ◽  
N. R. Morgenstern
Keyword(s):  
Stress State ◽  
Void Ratio ◽  
Boundary Surface ◽  
The State ◽  
Loose Sand ◽  
Saturated Sand ◽  
Deviator Stress ◽  
Straight Line ◽  
State Boundary ◽  
State Boundary Surface

A state-boundary surface defines a boundary in stress – void-ratio space above which no stress state can exist. The applicability of the state-boundary surface for sand has not gained widespread attention primarily because sand is not generally considered to be a difficult soil from a design point of view apart from liquefaction. Liquefaction is a phenomenon usually encountered in very loose cohesionless materials. An experimental study relating the drained and undrained behavior of very loose saturated sand is presented. It is shown that the post-peak portion of undrained stress paths travels along the state boundary and that the state boundary can be approximated by a straight line. The slope of this straight line appears to stay constant for very loose sand. There are potentially an infinite number of these lines, which form a three-dimensional surface in deviator stress – effective mean normal stress – void-ratio space. Previously published results by various researchers are used to confirm the existence of the state boundary. This surface is mathematically defined in deviator stress – effective mean normal stress – void-ratio space. Loose saturated sand samples loaded drained from a stress state on or very close to the state boundary surface essentially travel along the state boundary surface. Key words : sand, collapse, liquefaction, stress path, state boundary, triaxial test.

An interpretation of structural degradation for three natural clays

2004 ◽  
Vol 41 (3) ◽  
pp. 392-407 ◽  
Author(s):  
Luigi Callisto ◽  
Sebastiano Rampello
Keyword(s):  
Boundary Surface ◽  
Constitutive Models ◽  
The State ◽  
Isotropic Hardening ◽  
Plastic Strains ◽  
Structure Degradation ◽  
Stress Components ◽  
History Of ◽  
State Boundary ◽  
Natural Clays

The mechanical behaviour of natural clays is influenced by the degradation of the microstructure induced by the applied loads. The consequence of progressive damage to the natural microstructure is that it is not possible to describe the state of the soil in terms of effective stress components and void ratio only, and therefore it is not possible to locate a unique state boundary surface by normalizing stresses with respect to the equivalent pressure. In this paper it is shown that, by defining a normalizing pressure that accounts for the progressive loss of structure occurring during a test, the state of the soil during loading can be completely described in a normalized stress space. The laws linking the normalizing pressure to the degree of microstructure disruption are derived from the isotropic hardening laws of two constitutive models recently proposed for natural soils. The normalizing procedure is applied to the experimental results obtained on three natural clays of different depositional origin and with different mechanical properties. For the three clays, the parameters describing structure degradation permit the assessment of the rate of loss of structure with plastic strains. For the clays examined, the volumetric plastic strains are seen to play a major role, compared to the deviatoric plastic strains, in causing progressive disruption of the microstructure. Lastly, it is shown that the initial degree of structure and the rate of structure degradation can be related to the depositional conditions and the stress history of the clay deposits.Key words: clays, compressibility, fabric–structure of soils, laboratory tests, plasticity, shear strength.

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