Search

Swallowing of large objects and humans by quicksand fascinated writers for long time. Previously, it was believed that sand must contain liquid to achieve such characteristics. However, recently it has been proposed that even undampened loose sand (like in deserts) can swallow large objects and investigated in this paper. In this study, numerical simulations are performed using computational fluid dynamics (CFD) and discrete element method (DEM). The transition from packed to quicksand like state in granular material is obtained by passing gas near to minimum fluidization velocity and keeping bed stationary. It is observed in simulations that dry quicksand acts more like a fluid and the granular drag force due to penetration of intruder becomes isotropic and depth independent which is a deviation from packed bed. At the end of paper, the physics behind this behavior is explained by comparing force chains formed in packed and dry quicksand.

The present paper reports the application of a 2-D coupled fluid-particle simulation model with no macroscopic assumptions to the seepage failure of saturated granular soils. The basic problem of the seepage failure of a horizontal ground with an embedded sheet pile, where the system size is set to be 200 × 100 mm and the average diameter of the soil particle is 550 μ m, is numerically investigated. Both the seepage flow and the motion of the soil particles are directly solved by coupling the lattice Boltzmann method and the discrete element method. The goal of this study is to confirm that the 2-D direct simulation can be performed on the scale of a model experiment with soil particles that correspond in size to that of real sand. As a result of the analysis, it is shown that a typical series of behavior for seepage failure, where boiling and heaving initially occur on the downstream side near the sheet pile and finally lead to quicksand, can be seamlessly reproduced. Comparing the cases with different initial void ratios, it is found that the deformation area and the rates of the failure process can be varied according to the packing state. By tracking the velocity of each soil particle, it is visually shown that seepage failure begins to occur in the corner areas of the sheet pile much earlier than the onset of quicksand. By focusing on the fluid force acting on that particle, it is seen that the relatively large values for the hydrodynamic forces are concentrated on the upstream side before the beginning of uplift. In addition, by a comparison with two theories for the critical hydraulic gradient, the current limitations and problems of the proposed method are also summarized.

To obtain a comprehensive understanding on sand production and main factors affecting sand production in unconsolidated quicksand oil reservoirs during their production stage, the sand production processes under different conditions have been modelled. The modelling experiment was carried out on unconsolidated sand formation model made of water washed white sand, clay (kaolinite) and distilled water, by using a newly developed sanding modelling apparatus. The effects of drag force acting on the formation and formation cementation on sand production were analysed. The experimental results show sand and oil production rates both increase with the rise of drag force acting on the formation and decrease with the increase of cement content, and the sand production rate even approaches zero at high cement content. The reservoir with higher pressure is more likely to produce sand during development due to higher drag force, and drag force and effective formation stress jointly affect oil production. Therefore, the sand production rate can be estimated according to clay content, and proper sanding prevention measures can be taken correspondingly. In some cases, sand production in oil reservoirs can be much greater than that in gas reservoirs. Key words: quicksand reservoir, sand production, oil recovery, clay content, cementation degree, drag force

The widespread use of social media and its potential to hinder academic performance has received the attention of researchers and is a growing concern of educators. This phenomenological study explored the perceived impact of social media on the educational experiences of university students in the United States, both in and out of the classroom. Analysis of semi-structured interviews revealed several pervasive themes, all of which can be viewed as barriers to academic success. Participants reported that using social media during academic activities diminishes achievement, increases the amount of time it takes to complete tasks, and reduces how much information students retain from study and lecture sessions. Additionally, participants indicated how a lack of situational and topic interest increases social media's temptation. We argue that educators and students would benefit from a more complete understanding of social media's role as a barrier to academic success. Implications for educators are discussed.

Behavioral economics lacks empirical evidence on some foundational empirical questions. We adapt standard elicitation methods to measure multiple behavioral factors per person in a representative U.S. sample, along with financial condition, cognitive skills, financial literacy, classical preferences and demographics. Individually, B-factors are prevalent, distinct from other decision inputs, and correlate negatively with financial outcomes in richly-conditioned regressions. Conditioning further on other B-factors does not change the results, validating common practice of modeling B-factors separately. Corrections for low task/survey effort modestly strengthen the results. Our findings provide bedrock empirical foundations for behavioral economics, and offer methodological guidance for research designs.

Understanding the interaction of the groundwater seepage flow and sediment transport along permeable boundaries is essential for managing soil beds and bank erosion. A significant bank failure may occur due to sediment transport under the boiling condition. In the present study, an experiment is conducted to investigate the effects of injection or upward seepage on the critical shear stress of a cohesionless soil bed subjected to surface flow. The upward seepage force acting on the soil bed particles may reduce the virtual weight of the particles. In turn, it may also reduce the critical shear stress acting on the particles. A theoretical analysis examines how the upward seepage force acts to modify the critical shear stress for the sediment entrainment due to the increase in the hydraulic gradient of the seepage flow. A force analysis reveals that the ratio of the critical shear stress with seepage to that without seepage is dependent on the ratio of the hydraulic gradient of seepage to its value at the quicksand condition. A test apparatus was built, and the effects of injection on the critical shear stress of cohesionless soil bed particles were measured. An acrylic channel with a rectangular cross section was prepared, and a section of a cohesionless soil bed subjected to an upward seepage flow was installed at the bottom of the channel. The experiment demonstrates that the induced seepage affects the dynamics of the channel flow, even though the magnitude of the seepage flow velocity is significantly smaller than that of the free surface water flow. The test results show that the dimensionless critical shear stress of the cohesionless soil bed particles decreases slightly as the hydraulic gradient of the seepage flow is increased when critical shear stress is determined at the upstream edge of the seepage zone. Furthermore, the dimensionless critical shear stress decreases sharply with the increment of the hydraulic gradient of the seepage flow when critical shear stress is determined in the seepage zone. However, it does not decrease in either case, as was theoretically assumed, even when the hydraulic gradient approaches to the critical hydraulic gradient or the quicksand condition.

The broad field of public relations is plagued by difficulties of definition, none more problematic than the definitional challenges facing issue management and crisis management. After considering the need for commonly understood language as a basis for meaningful discourse, the paper identifies the particular reasons for ongoing ambiguity in issue and crisis management and charts some distinct approaches which have developed within each discipline. It then analyzes how these evolutionary changes are creating further difficulties for defining the interplay between the two, and identifies a more integrated process approach focused on characterizing clusters of activities.

A coupled continuum-discrete hydromechanical model was utilized to analyze the meso-scale pore fluid flow and micro-scale solid phase deformation of saturated granular soils. The fluid motion was idealized using averaged Navier–Stokes equations and the discrete element method was employed to model the solid particles. Well established semi-empirical relationships were used to quantify the fluid–particle interactions. Numerical simulations were conducted to investigate the mechanisms of granular deposit liquefaction in the presence of a critical upward pore fluid flow as well as when subjected to a dynamic base excitation. The outcome of these simulations was consistent with experimental observations and revealed valuable information on the micro-mechanical characteristics of soil liquefaction and associated loss of stiffness and strength.

Grain storage containers not only present inherent dangers to the operators, but also to the rescuers if someone falls in. Here we report the rescue of a patient from a grain container using a novel technique involving a cylinder placed around the patient. This allowed the grain to be sucked out from around the patient and enabled his rescue uninjured. The rescue action was complicated by acute chest pain in the patient while he was submerged in the grain, and a severe asthma attack in the emergency physician. The rescue and the dilemmas encountered are described together with a review of the relevant literature.

This commentary highlights some of the major moral and ethical dilemmas illustrated by authors in this special issue. From an ethical viewpoint, the complexity of evaluation activities is likened to “quicksand” terrain in which directional or warning signs should be erected to aid personal choices when such issues are encountered. However, even previous training and personal introspection are inadequate to completely avoid, circumvent, or handle a specific situation because of its complexity and the competing values inherent in ethical choices.

Artificial freezing of ground by refrigerating machines requires considerable power and expense, so it is comparatively seldom applied and almost always for a short period. In the regions of severe climate, seasonal freezing and long-term preservation of low temperatures in a mass of frozen ground can compete in effectiveness and economy with the traditional methods of loose ground stabilization, quicksand and boggy—clayey deposits, in particular. In practice, different methods and systems are applied for freezing the ground using the cold atmosphere air as a heat-absorbing medium. Systems with forced pumping of the intermediate heat carrier or of the air itself are more economic than machine freezing, but they are unreliable and maintenance is very expensive. Freezing devices using natural circulation of a single-phase and double-phase heat carrier in hermetically sealed cavities or thermosiphons permit effective control of the temperature regime of the ground in the seasonal and annual cycles of temperature variation of the ground and atmosphere air with the minimum operating expense. The paper considers the operational features of freezing systems and different devices, and gives examples of the utilization of artificially frozen ground in hydraulic structures and in foundations of industrial buildings and dwelling houses. The possibility of creating artificially frozen masses used as foundations of the structures built in severe climatic regions is considered, and examples of the existing buildings constructed on the artificial lenses of frozen ground are given.

The long and successful experience of the Dutch in recovering land from the sea and protecting it from inundation needs no emphasis. Even their ingenuity in civil engineering has been challenged, however, in the design and construction of a storm-surge barrier across the Eastern Scheldt, for it has virtually to be built on quicksand. This article describes the way in which the problem has been solved by laying huge prefabricated filter mattresses on the seabed to provide a secure foundation against the assaults of the highest tides.

The rapid increase of physical distribution costs relative to other categories has resulted in a renewed interest in the analysis of transport operations. One of the most common problems is that of vehicle replacement, and in this paper we present an analysis of real data. The methodology is developed paying due regard to the role of quantitative analysis in the decision-making process, and the sort of data which is readily available in most transport departments. A traditional discounted cost model is presented and this is followed by a productivity-based analysis, which is shown to be an improvement. The latter generates optimal solutions and is flexible enough to carry out considerable sensitivity analysis.

Can we study the future “rationally” and “scientifically”? This paper examines the methods now in use and finds the assumptions shaky, the tools faulty, and the implications dangerous. With data as the driver, analysis the watchword, quantification the rule, and model-building the prime preoccupation, futurology rests heavily on two key pillars, the information base and cost/benefit calculations. Because these are shown to rest on quicksand, the elaborate methodological structure based on them totters precariously.