Collapse behavior of sand

1993 ◽  
Vol 30 (4) ◽  
pp. 569-577 ◽  
Author(s):  
S. Sasitharan ◽  
P.K. Robertson ◽  
D.C. Sego ◽  
N.R. Morgenstern
Keyword(s):  
Steady State ◽  
Void Ratio ◽  
Boundary Surface ◽  
Stress Path ◽  
Published Data ◽  
Stress Deviator ◽  
State Strength ◽  
Flow Slides ◽  
State Boundary ◽  
Collapse Behavior

Loose cohesionless materials can collapse during either static or dynamic loading, resulting in a rapid buildup of pore pressure and associated reduction in shear resistance. As the cohesionless material collapses, it rapidly looses resistance until the acting shear stress decreases to the available residual or steady-state strength. Specially designed stress-path testing has been performed on sand to investigate this collapse process. Results from this test program and previously published data show that a state boundary can be defined when a cohesionless material moves from peak to steady state along a constant void ratio stress path regardless of whether it is loaded drained or undrained. Further, it is demonstrated that the state boundary represents a surface in the effective mean normal stress–deviator stress–void ratio space. Hence, flow slides and liquefaction can be initiated when the stress path followed during either drained or undrained loading attempts to cross this state boundary surface. Key wordy : sand, collapse, liquefaction, stress path, state boundary, triaxial test.

Stress path and steady state

1990 ◽  
Vol 27 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Y. P. Vaid ◽  
E. K. F. Chung ◽  
R. H. Kuerbis
Keyword(s):  
Steady State ◽  
Effective Stress ◽  
Void Ratio ◽  
Triaxial Compression ◽  
Stress Path ◽  
Stress Space ◽  
Sand Liquefaction ◽  
State Strength ◽  
The Difference ◽  
State Stress

The effect of stress path on the steady state line of a liquefiable sand is investigated. Results from undrained triaxial compression and extension tests on water-deposited sands show that the steady state line of a given sand, though unique in the effective stress space, is not so in the void ratio – effective stress space. The sand is contractive over a much larger range of void ratios in extension than in compression. While a single steady state line emerges for compression loading, extension loading yields several lines, each characteristic to a given deposition void ratio. All these extension lines lie to the left of the compression line in void ratio – effective stress space. Thus at a given void ratio, steady state strength is smaller in extension than in compression, the difference increasing as the sand becomes looser. The implications of the results are discussed in relation to practical design. Key words: sand, liquefaction, steady state, stress path.

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.

scholarly journals On equivalent granular void ratio and steady state behaviour of loose sand with fines

2008 ◽  
Vol 45 (10) ◽  
pp. 1439-1456 ◽  
Author(s):  
M. M. Rahman ◽  
S. R. Lo ◽  
C. T. Gnanendran
Keyword(s):  
Steady State ◽  
Void Ratio ◽  
Soil Mechanics ◽  
Back Analysis ◽  
B Value ◽  
Published Data ◽  
Factors Affecting ◽  
State Variable ◽  
Cyclic Resistance ◽  
Alternative State

Void ratio has traditionally been used as a state variable for predicting the liquefaction behaviour of soils under the critical state soil mechanics framework. Recent publications show that void ratio may not be a good state variable for characterizing sand with fines. An alternative state variable referred to as the equivalent granular void ratio has been proposed to resolve this problem. To calculate this alternative state variable, a b parameter is needed. This b parameter represents the fraction of fines that actively participate in the force structure of the solid skeleton. However, predicting the value of b is problematic. Most, if not all, of the b values reported were determined by case-specific back-analysis, that is, the b value was selected so that a single correlation between equivalent granular void ratio and the measured steady state strength (or cyclic resistance) could be achieved. This paper examines the factors affecting the b value based on published work on binary packing. This leads to a simple semi-empirical equation for predicting the value of b based on fines size and fines content. Published data appear to be in support of the proposed equation. A series of experiments were conducted on a specially designed sand–fines type to provide additional validation of the proposed equation and to reinforce the use of equivalent granular void ratio in a more generalized context.

The Nerlerk berm case history: some considerations for the design of hydraulic sand fills

1991 ◽  
Vol 28 (4) ◽  
pp. 601-612 ◽  
Author(s):  
Jean-Marie Konrad
Keyword(s):  
Steady State ◽  
Large Scale ◽  
Void Ratio ◽  
Strain Softening ◽  
Back Analysis ◽  
Confining Stress ◽  
Hydraulic Fill ◽  
State Strength ◽  
Undrained Strength ◽  
Unique Relationship

Back-analyses of recent large-scale slides during the hydraulic placement of an articial sand island at the Nerlerk site (Beaufort Sea) using different methods have resulted in contradictory conclusions with respect to the state of the fill. All the interpretation methods assume a unique relationship between steady-state strength and void ratio. This assumption is, however, not verified, since steady-state strength depends also on effective confining stress. This paper presents the results of a back-analysis at the Nerlerk site using a modified concept proposed by the author which isbased on nonunique values of steady-state strength for a given sand. It is established that the density conditions at Nerlerk, on average at a relative density of about 40%, and the initial stress conditions are conducive to strain softening, with a steady-state strength corresponding to the minimum strength defined by the LF line. For Nerlerk sand,the minimum undrained strength is about 18% of the steady-state strength determined with conventional methods using high confining stresses. The Nerlerk berm failures were thus "liquefaction" slides induced most likely by progressive straining. Key words: sand, undrained, strength, steady state, hydraulic fill.

Static liquefaction of sands under multiaxial loading

1998 ◽  
Vol 35 (2) ◽  
pp. 273-283 ◽  
Author(s):  
M Uthayakumar ◽  
Y P Vaid
Keyword(s):  
Steady State ◽  
Hollow Cylinder ◽  
Void Ratio ◽  
Friction Angle ◽  
Stress Path ◽  
Shear Loading ◽  
Multiaxial Loading ◽  
Fundamental Study ◽  
Torsional Shear ◽  
Loading Direction

A fundamental study of the undrained behaviour of sands under multiaxial loading is presented. The investigation was carried out using Fraser River and Syncrude sands in a hollow cylinder torsional shear device. Shear loading was carried out under strain control to capture the postpeak strain-softening characteristics of loose sands. It is shown that the undrained response of loose sands is highly dependent on the loading direction. The friction angle mobilized at phase transformation and steady state is a unique material property, independent of the mode of loading, direction of principal stress and initial consolidation stress, and void ratio state. There is no unique relationship between steady state strength and void ratio which is independent of stress path and the level of initial confining stress.Key words: anisotropy, hollow cylinder torsional shear, liquefaction, sand, simple shear, triaxial.

New framework for volumetric constitutive behaviour of compacted unsaturated soils

2012 ◽  
Vol 49 (11) ◽  
pp. 1227-1243 ◽  
Author(s):  
Jayantha Kodikara
Keyword(s):  
Unsaturated Soils ◽  
Boundary Surface ◽  
Failure Surface ◽  
Constitutive Modelling ◽  
Tensile Failure ◽  
Compacted Soils ◽  
Compaction Curve ◽  
State Boundary ◽  
Observed Behaviour ◽  
New Framework

Volumetric behaviour is a fundamental consideration in unsaturated soil constitutive modelling. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses such as swelling and collapse under wetting and shrinkage and cracking during drying. While significant advances have been made, it is still difficult to generally explain all patterns of behaviour. This paper presents a new framework for modelling volumetric response of unsaturated soils with emphasis on compacted soils. The framework uses void ratio (e), moisture ratio (ew), and net stress (p) as the main constitutive variables and suction as a dependent variable. This choice of ew as a main constitutive variable is theoretically sound and is more attractive than the use of suction, which is relatively difficult to measure and displays significant hysteresis during drying and wetting. The framework incorporates the well-known compaction curve making it easily applicable to practical situations. Within the overall e–ew–p space, the operative space is constrained by three main surfaces; namely, loading–wetting state boundary surface, tensile failure surface, and the saturated plane. The conceptual basis for these state surfaces is described and the framework is qualitatively validated against observed behaviour of compacted soils.

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