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.

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.

Influence of generalized initial state and principal stress rotation on the undrained response of sands

2002 ◽  
Vol 39 (1) ◽  
pp. 63-76 ◽  
Author(s):  
S Sivathayalan ◽  
Y P Vaid
Keyword(s):  
Principal Stress ◽  
Strain Softening ◽  
Principal Stresses ◽  
Initial Stress State ◽  
Stress Rotation ◽  
Bedding Planes ◽  
State Strength ◽  
Major Principal Stress ◽  
Undrained Strength ◽  
Static Shear

The dependence of the undrained behaviour of sand on the initial stress state and the orientation of principal stresses with respect to the bedding planes is assessed under generalized loading paths using hollow cylinder torsional shear tests. The undrained tests were carried out using displacement-controlled loading to confidently capture the post-peak strain-softening response. Undrained behaviour of sands under identical initial states is shown to be dependent on the direction of principal stresses, during and prior to undrained shear, in relation to the direction of bedding planes. The minimum undrained strength of the strain-softening sand is found to be highly influenced by the initial stress state (confining stress, direction of principal stresses, and static shear), even though the friction angle mobilized at the instant of minimum strength is unique. A mere rotation of principal stresses at constant deviator stress alone can lead to a strain-softening response that may culminate in limited or unlimited flow deformation. The susceptibility of sand to liquefaction due to stress rotation increases as the direction of the major principal stress approaches the orientation of the bedding plane. The potential for flow deformation is strongly dependent on the direction of the major principal stress in relation to the bedding planes, and the steady state strength is not uniquely related to the void ratio alone.Key words: liquefaction, hollow cylinder torsion test, principal stress direction, static shear, steady state strength, minimum undrained strength.

Undrained shear strength for liquefaction flow failure analysis

1995 ◽  
Vol 32 (5) ◽  
pp. 783-794 ◽  
Author(s):  
J.-M. Konrad ◽  
B.D. Watts
Keyword(s):  
Steady State ◽  
Empirical Relationship ◽  
Reference Value ◽  
Strength Loss ◽  
State Strength ◽  
Flow Failure ◽  
Undrained Strength ◽  
Hydraulic Fills ◽  
Extreme Sensitivity ◽  
The Stability

An important factor in evaluating the stability of hydraulic fills against flow sliding is the undrained steady-state strength mobilized in the field. This paper proposes an empirical relationship between three factors: the undrained strength back-calculated from fills that failed by flow sliding, equivalent clean sand normalized blow-count values, and soil-specific parameters from steady-state laboratory testing. It is shown that Suo, which is a reference value of steady-state strength at maximum void ratio, is an important soil parameter. The proposed method offers an explanation for the performance of many artificial sand islands in the Beaufort Sea, indicates the extreme sensitivity of Suo to soil type and the usefulness of Suo for assessing the potential strength loss of soils for use in safety assessments of existing hydraulic fills. Key words : undrained strength, liquefaction, sand, field, case-histories, analysis.

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.

The liquefaction of sands, a collapse surface approach

1985 ◽  
Vol 22 (4) ◽  
pp. 564-578 ◽  
Author(s):  
J. A. Sladen ◽  
R. D. D'Hollander ◽  
J. Krahn
Keyword(s):  
Steady State ◽  
Large Scale ◽  
Soil Mechanics ◽  
Limit Equilibrium ◽  
Three Dimensional ◽  
Beaufort Sea ◽  
Triaxial Tests ◽  
Necessary Condition ◽  
State Testing ◽  
Hydraulic Fill

Recent large-scale slides occurring during the hydraulic placement of an artificial island berm in the Beaufort Sea resulted from the liquefaction of the berm sand. Subsequent laboratory tests and back analyses have led to advancements in the understanding of the liquefaction potential of sand. Analyses of undrained triaxial tests, undertaken to measure steady state parameters, suggest that there is a "collapse surface" in three-dimensional void ratio – shear stress – normal stress space. A necessary condition for liquefaction is that the soil state lie on this surface. This collapse surface concept is fundamentally an extension of the steady state concepts proposed by others, and in many respects follows the principles of critical state soil mechanics. Replotted published tests support the concept. Parameters used to describe the position of the surface are termed collapse parameters. These can be converted into parameters analogous to Mohr–Coulomb failure parameters and can therefore be used in conventional limit equilibrium stability analyses. Utilizing these parameters overcomes limitations inherent in previously proposed undrained steady state analysis methods. These concepts also provide a basis for a rational explanation of the Beaufort Sea hydraulic fill slides. Key words: liquefaction, sand, hydraulic fill, slope stability, steady state testing.

Cyclic Breathing Simulations in Large Scale Models of the Lung Airway From the Oronasal Opening to the Terminal Bronchioles

2012 ◽  
Author(s):  
D. Keith Walters ◽  
Greg W. Burgreen ◽  
Robert L. Hester ◽  
David S. Thompson ◽  
David M. Lavallee ◽  
...  
Keyword(s):  
Steady State ◽  
Boundary Conditions ◽  
Large Scale ◽  
Whole Body ◽  
Patient Specific ◽  
Cfd Simulations ◽  
Reduced Order ◽  
Scale Models ◽  
Steady State Simulation ◽  
Conducting Zone

Computational fluid dynamics (CFD) simulations were performed for unsteady periodic breathing conditions, using large-scale models of the human lung airway. The computational domain included fully coupled representations of the orotracheal region and large conducting zone up to generation four (G4) obtained from patient-specific CT data, and the small conducting zone (to G16) obtained from a stochastically generated airway tree with statistically realistic geometrical characteristics. A reduced-order geometry was used, in which several airway branches in each generation were truncated, and only select flow paths were retained to G16. The inlet and outlet flow boundaries corresponded to the oronasal opening (superior), the inlet/outlet planes in terminal bronchioles (distal), and the unresolved airway boundaries arising from the truncation procedure (intermediate). The cyclic flow was specified according to the predicted ventilation patterns for a healthy adult male at three different activity levels, supplied by the whole-body modeling software HumMod. The CFD simulations were performed using Ansys FLUENT. The mass flow distribution at the distal boundaries was prescribed using a previously documented methodology, in which the percentage of the total flow for each boundary was first determined from a steady-state simulation with an applied flow rate equal to the average during the inhalation phase of the breathing cycle. The distal pressure boundary conditions for the steady-state simulation were set using a stochastic coupling procedure to ensure physiologically realistic flow conditions. The results show that: 1) physiologically realistic flow is obtained in the model, in terms of cyclic mass conservation and approximately uniform pressure distribution in the distal airways; 2) the predicted alveolar pressure is in good agreement with previously documented values; and 3) the use of reduced-order geometry modeling allows accurate and efficient simulation of large-scale breathing lung flow, provided care is taken to use a physiologically realistic geometry and to properly address the unsteady boundary conditions.

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