scholarly journals Static Liquefaction Capacity of Saturated Undisturbed Loess in South Jingyang Platform

Water ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 2298 ◽  
Author(s):  
Rui-Xin Yan ◽  
Jian-Bing Peng ◽  
Jin-Yuan Zhang ◽  
Shao-kai Wang
Keyword(s):  
Steady State ◽  
Strain Softening ◽  
Shaanxi Province ◽  
Triaxial Tests ◽  
Pore Throat ◽  
Long Distance ◽  
Particle Rearrangement ◽  
Static Liquefaction ◽  
Small Pore ◽  
Loess Landslides

According to a previous geological investigation, high-speed and long-distance loess landslides in the South Jingyang platform in Shaanxi Province are closely related to the static liquefaction of loess. Considering the typical loess landslides in this area, isotropic consolidated undrained (ICU) triaxial tests and scanning electron microscopy analyses were conducted in this study. The main conclusions are as follows: (1) The stress-strain curves indicate strong strain softening under different confining pressures. The pore water pressure increases significantly and then remains at a high level; (2) The liquefaction potential index (LPI) shows an increasing trend followed by stabilization; the larger the LPI is, the smaller the state parameter (Ψ) is. The steady-state points of the loess are in the instability region; however, the steady-state strength is not zero; (3) Based on the ICU test results, the average pore diameter decreases; the shape ratio remains essentially unchanged; and the fractal dimension and roundness show different trends. The proportions of the macropore and mesopore decrease; that of the small pore increases slightly; and that of the micropore increases significantly; (4) The compression deformation of the highly spaced pores causes rapid strain hardening. A rapid strain softening results from the pore throat blockage at the beginning of particle rearrangement and reorganization. A stable strain softening is related to the agglomeration blocking of the reconstructed pore throat in the gradually stable stage of particle rearrangement and reorganization.

scholarly journals Instability of Compacted Residual Soil

Geosciences ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 403
Author(s):  
Sainulabdeen Mohamed Junaideen ◽  
Leslie George Tham ◽  
Chack Fan Lee
Keyword(s):  
Steady State ◽  
State Parameter ◽  
Triaxial Tests ◽  
Residual Soil ◽  
Test Results ◽  
Residual Soils ◽  
Constant Shear ◽  
Static Liquefaction ◽  
Constant Shear Stress ◽  
Stress Ratios

Static liquefaction of loose sands has been observed to initiate at stress ratios far less than the steady-state stress ratio. Different collapse surface concepts largely based on undrained triaxial test results have been proposed in the literature to explain the above instability phenomenon of loose sands. Studies of the instability behavior of fill material derived from residual soils remain limited. The present study investigated the instability behavior of a compacted residual soil using the conventional undrained triaxial tests and specially equipped constant shear triaxial tests. The test results were characterized in the p’: q: v space using the current state parameter with respect to the steady-state line for the residual soil. A modified collapse surface that has gradients varying with p’ and v was proposed for the loose residual soil to represent the instability states of undrained loading. Under constant shear stress conditions, the soil can mobilize stress ratios higher than those defined by the modified collapse surface. An instability surface was therefore presented for the instability states reached in static loading. Further, an alternative method of deducing the instability surface from the undrained stress paths was introduced.

Static liquefaction as a possible explanation for the Merriespruit tailings dam failure

2001 ◽  
Vol 38 (4) ◽  
pp. 707-719 ◽  
Author(s):  
A B Fourie ◽  
G E Blight ◽  
G Papageorgiou
Keyword(s):  
South Africa ◽  
Steady State ◽  
Companion Paper ◽  
Dam Failure ◽  
Triaxial Tests ◽  
Tailings Dam ◽  
Failure Investigation ◽  
Static Liquefaction ◽  
Gold Tailings

In 1994 the Merriespruit gold tailings dam in South Africa failed, resulting in 17 deaths. The post-failure investigation provided no explanation as to why the catastrophic flow failure, which contradicted all previous experiences of failures of gold tailings dams in South Africa, occurred. The documented history of the dam describes insufficient freeboard provision and often poor pool control, which is argued to have resulted in some areas of the dam having high in situ void ratios. Some of the undrained triaxial tests carried out on specimens obtained from zones adjacent to the failure scar exhibited nondilative behaviour. Laboratory triaxial tests that were conducted on reconstituted specimens and are reported in a companion paper defined a series of steady state lines that were dependent on the particle-size distribution of the tailings. Void ratios obtained from undisturbed samples taken during the post-failure investigation are compared with these steady state lines and it is shown that an appreciable percentage of the specimens were likely to have been contractant. The inference drawn is that a large volume of tailings was in a metastable state in situ and overtopping and erosion of the impoundment wall exposed this material, resulting in static liquefaction of the tailings and a consequent flow failure.Key words: static liquefaction, gold tailings, Merriespruit, failure.

scholarly journals Research of the Behavior of Clay Materials with Double Porosity

2021 ◽  
Vol 13 (6) ◽  
pp. 3219
Author(s):  
Hynek Lahuta ◽  
Luis Andrade Pais
Keyword(s):  
Double Porosity ◽  
Strength Properties ◽  
Triaxial Tests ◽  
Building Structures ◽  
Foundation Soil ◽  
Problematic Use ◽  
The North ◽  
Static Liquefaction ◽  
Confinement Stress ◽  
Clay Materials

This contribution presents results from a series of compression and undrained triaxial tests to study the mechanical behavior of dump clay from the north of Bohemia. The use of these materials as a foundation for construction can’t be achieved without the adoption of some precautions. This comes from embankment, formed by digging the ground (altered claystone), up to the level of coal mining which is in a sub horizontal stratigraphic layer. A potential static liquefaction behavior was observed in undrained tests for high confinement stress. A structural collapse was noticed with the results obtained in the triaxial test. This collapse is characterized by an unexpected large decrease in deviator and mean effective stress. The soils formed have strength properties that are potentially dangerous. These concepts can improve the use of these kinds of soils in geotechnical engineering work. It continues and expands the results obtained in previous research, especially the future problematic use of these materials as the foundation soil for line or building structures.

scholarly journals Microscale Pore Throat Differentiation and Its Influence on the Distribution of Movable Fluid in Tight Sandstone Reservoirs

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Fengjuan Dong ◽  
Xuefei Lu ◽  
Yuan Cao ◽  
Xinjiu Rao ◽  
Zeyong Sun
Keyword(s):  
Ordos Basin ◽  
Pore Throat ◽  
Tight Sandstone ◽  
Throat Radius ◽  
Thin Sections ◽  
Small Pore ◽  
Sandstone Reservoir ◽  
Sandstone Reservoirs ◽  
Classification Evaluation ◽  
Better Than

Tight sandstone reservoirs have small pore throat sizes and complex pore structures. Taking the Chang 6 tight sandstone reservoir in the Huaqing area of the Ordos Basin as an example, based on casting thin sections, nuclear magnetic resonance experiments, and modal analysis of pore size distribution characteristics, the Chang 6 tight sandstone reservoir in the study area can be divided into two types: wide bimodal mode reservoirs and asymmetric bimodal mode reservoirs. Based on the information entropy theory, the concept of “the entropy of microscale pore throats” is proposed to characterize the microscale pore throat differentiation of different reservoirs, and its influence on the distribution of movable fluid is discussed. There were significant differences in the entropy of the pore throat radius at different scales, which were mainly shown as follows: the entropy of the pore throat radius of 0.01~0.1 μm, >0.1 μm, and <0.01 μm decreased successively; that is, the complexity of the pore throat structure decreased successively. The correlation between the number of movable fluid occurrences on different scales of pore throats and the entropy of microscale pore throats in different reservoirs is also different, which is mainly shown as follows: in the intervals of >0.1 μm and 0.01~0.1 μm, the positive correlation between the occurrence quantity of movable fluid in the wide bimodal mode reservoir is better than that in the asymmetric bimodal mode reservoir. However, there was a negative correlation between the entropy of the pore throat radius and the number of fluid occurrences in the two types of reservoirs in the pore throat radius of <0.01 μm. Therefore, pore throats of >0.1 μm and 0.01~0.1 μm play a controlling role in studying the complexity of the microscopic pore throat structure and the distribution of movable fluid in the Chang 6 tight sandstone reservoir. The above results deepen the understanding of the pore throat structure of tight sandstone reservoirs and present guiding significance for classification evaluation, quantitative characterization, and efficient development of tight sandstone reservoirs.

Analysis of steady-state stability of long-distance transmission systems

1978 ◽  
Vol 98 (4) ◽  
pp. 63-72
Author(s):  
Toshihiko Saito ◽  
Kozo Aratame ◽  
Hiromichi Sato ◽  
Jiro Nagasaka
Keyword(s):  
Steady State ◽  
Long Distance ◽  
Transmission Systems ◽  
Long Distance Transmission ◽  
Steady State Stability

Investigation of Flow Stress Behavior and Microstructural Evolution of 7050 Al Alloy

2007 ◽  
Vol 546-549 ◽  
pp. 1065-1068 ◽  
Author(s):  
You Ping Yi ◽  
Hua Chen ◽  
Yong Cheng Lin
Keyword(s):  
Steady State ◽  
Strain Softening ◽  
Type Equation ◽  
Al Alloy ◽  
Compression Tests ◽  
Hollomon Parameter ◽  
Deformation Behaviors ◽  
Three Stages ◽  
Increasing Temperature ◽  
State Stress

The plastic deformation behaviors of 7050 Al alloy were investigated by compression tests at temperatures ranging of 250°C450°C under constant strain rates of 0.01s−1, 1s−1 and 10s−1. The results showed that all the flow curves consisted of three stages, i.e. strain-hardening, strain-softening and steady state-strain. Initially, the stress rises steeply at microstrain deformation, and then increases at a decreased rate, followed by a strain-softening until a steady state stress. The stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in an exponent-type equation, 1 19 7.202 σ p 80.71 sinh (1.64 10 Z) = ⋅ −  × − ⋅ −  . Elongated grains with serrations developed in the grain boundaries were observed; the dynamic recrystallization (DRX) occurs with increasing temperature and dislocation density, and the shape of grain at steady state is nearly equiaxial. It can be concluded that the DRX phenomenon is sensitive to the temperature and the dynamic flow softening is mainly as the result of dynamic recovery and DRX.

Uniqueness of steady state and liquefaction potential

1994 ◽  
Vol 31 (1) ◽  
pp. 132-139 ◽  
Author(s):  
D. Negussey ◽  
M.S. Islam
Keyword(s):  
Steady State ◽  
Bedding Plane ◽  
Triaxial Tests ◽  
Initial State ◽  
Liquefaction Potential ◽  
Initial Anisotropy ◽  
Anisotropic Consolidation ◽  
Stress States ◽  
Undrained Loading ◽  
Loading Form

A given sand is presumed to have a unique steady-state line. The proximity of an initial state to the steady-state line is considered to be a measure of liquefaction potential. This line of reasoning and application in practice is based on data obtained predominantly from triaxial tests in compression-mode loading. In such tests, relative orientations of bedding plane and principal stress directions remain fixed while stress states along actual failure surfaces may range from active to passive. This study examines the uniqueness of the steady state relative to the mode of loading, form of consolidation, and initial anisotropy as induced by bedding orientation. A sample-preparation method was developed to form triaxial samples with different bedding orientations. Steady states of a uniform sand reached under compressional and extensional modes of triaxial undrained loading of samples with different bedding orientation are compared. Effects of isotropic and anisotropic consolidation are examined. The results indicate the steady-state line obtained for compression-mode loading is different from and does not apply for extension-mode loading. Use of a compression side steady-state line for extension-mode failure states would result in overestimation of steady-state strengths and unconservative stability evaluations. Key words : anisotropy, compression, extension, liquefaction, sand, steady state, triaxial.

scholarly journals Emission Modes in Electrospray Thrusters Operating with High Conductivity Ionic Liquids

Aerospace ◽  
2020 ◽  
Vol 7 (10) ◽  
pp. 141
Author(s):  
Nolan M. Uchizono ◽  
Adam L. Collins ◽  
Anirudh Thuppul ◽  
Peter L. Wright ◽  
Daniel Q. Eckhardt ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Steady State ◽  
High Speed ◽  
Liquid Propellant ◽  
Long Distance ◽  
Flow Rates ◽  
Extraction Voltage ◽  
Wide Range ◽  
Emission Behavior ◽  
Definition Of

Electrospray thruster life and mission performance are strongly influenced by grid impingement, the extent of which can be correlated with emission modes that occur at steady-state extraction voltages, and thruster command transients. Most notably, we experimentally observed skewed cone-jet emission during steady-state electrospray thruster operation, which leads to the definition of an additional grid impingement mechanism that we termed “tilted emission”. Long distance microscopy was used in conjunction with high speed videography to observe the emission site of an electrospray thruster operating with an ionic liquid propellant (EMI-Im). During steady-state thruster operation, no unsteady electrohydrodynamic emission modes were observed, though the conical meniscus exhibited steady off-axis tilt of up to 15°. Cone tilt angle was independent over a wide range of flow rates but proved strongly dependent on extraction voltage. For the geometry and propellant used, the optimal extraction voltage was near 1.6 kV. A second experiment characterized transient emission behavior by observing startup and shutdown of the thruster via flow or voltage. Three of the four possible startup and shutdown procedures transition to quiescence within ∼475 μs, with no observed unsteady modes. However, during voltage-induced thruster startup, unsteady electrohydrodynamic modes were observed.

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