Evidence of dispersion in an artificial water-saturated sand sediment

Choosing the site for a new water well in rural southern Malawi is essentially a political process with competing priorities and stakeholders. For a new well (or borehole) to be sustainably used and maintained, the relevant stakeholders must be fully engaged in the siting process and given meaningful responsibility for the final siting decision. However, without sound technical information, a siting decision based solely on stakeholder priorities such as proximity to the headmans compound or accessibility to the center of population, may not result in a satisfactory borehole. Instead, in addition to stakeholder interests, we used a process that includes electrical resistivity tomography (ERT) as a tool to guide and constrain the local decision-making process. Within the region of the crystalline-basement aquifer, ERT profiles indicate variations in weathering thickness, hence aquifer storage. In a lacustrine setting, the ERT profile delineated a zone of moderately large resistivity associated with a deposit of fresh-water saturated sand. This ERT-derived technical information becomes one element in a comprehensive sociotechnical approach to the location of sustainable water resources. We used this sociotechnical approach to complete boreholes for all four villages in our project and have a high confidence that the villagers will be motivated to use and maintain these resources.

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Monitoring gas hydrate formation with magnetic resonance imaging in a metallic core holder

E3S Web of Conferences ◽

10.1051/e3sconf/20198902008 ◽

2019 ◽

Vol 89 ◽

pp. 02008

Author(s):

Mojtaba Shakerian ◽

Armin Afrough ◽

Sarah Vashaee ◽

Florin Marica ◽

Yuechao Zhao ◽

...

Keyword(s):

Magnetic Resonance Imaging ◽

Methane Hydrate ◽

Hydrate Formation ◽

Residual Water ◽

Saturated Sand ◽

Resonance Imaging ◽

The Core ◽

T2 Distribution ◽

Core Holder ◽

Water Saturated

Methane hydrate deposits world-wide are promising sources of natural gas. Magnetic Resonance Imaging (MRI) has proven useful in previous studies of hydrate formation. In the present work, methane hydrate formation in a water saturated sand pack was investigated employing an MRI-compatible metallic core holder at low magnetic ﬁeld with a suite of advanced MRI methods developed at the UNB MRI Centre. The new MRI methods are intended to permit observation and quantiﬁcation of residual ﬂuids in the pore space as hydrate forms. Hydrate formation occurred in the water-saturated sand at 1500 psi and 4 °C. The core holder has a maximum working pressure of 4000 psi between -28 and 80 °C. The heat-exchange jacket enclosing the core holder enabled very precise control of the sample temperature. A pure phase encode MRI technique, SPRITE, and a bulk T1-T2 MR method provided high quality measurements of pore ﬂuid saturation. Rapid 1D SPRITE MRI measurements time resolved the disappearance of pore water and hence the growth of hydrate in the sand pack. 3D π-EPI images conﬁrmed that the residual water was inhomogeneously distributed along the sand pack. Bulk T1-T2 measurements discriminated residual water from the pore gas during the hydrate formation. A recently published local T1-T2 method helped discriminate bulk gas from the residual ﬂuids in the sample. Hydrate formation commenced within two hours of gas supply. Hydrate formed throughout the sand pack, but maximum hydrate was observed at the interface between the gas pressure head and the sand pack. This irregular pattern of hydrate formation became more uniform over 24 hours. The rate of hydrate formation was greatest in the ﬁrst two hours of reaction. An SE-SPI T2 map showed the T2 distribution changed considerably in space and time as hydrate formation continued. Changes in the T2 distribution are interpreted as pore level changes in residual water content and environment.

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Laboratory studies on nitrate redistribution during the freezing process of a water-saturated sand system

Environmental Science and Pollution Research ◽

10.1007/s11356-018-3251-0 ◽

2018 ◽

Vol 26 (14) ◽

pp. 13818-13824 ◽

Cited By ~ 1

Author(s):

Huan Huang ◽

Mingzhu Liu ◽

Changfu Chen ◽

Guoxin Huang ◽

Honghan Chen

Keyword(s):

Freezing Process ◽

Saturated Sand ◽

Laboratory Studies ◽

Water Saturated

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Soil Cutting Processes: The Cutting of Water Saturated Sand

Volume 7: CFD and VIV; Offshore Geotechnics ◽

10.1115/omae2011-49233 ◽

2011 ◽

Author(s):

Sape A. Miedema

Keyword(s):

Pore Water ◽

Cutting Forces ◽

Water Vapor Pressure ◽

Cutting Process ◽

Shear Stresses ◽

Saturated Sand ◽

Pore Water Pressures ◽

Offshore Industry ◽

Cutting Processes ◽

Water Saturated

The cutting process in water saturated sand has been the subject of research in the dredging industry for decades already. The Dutch dredging industry started this research in the sixties, resulting in a number of models in the seventies and eighties (van Leussen & van Os (1987) and Miedema (1987 and later). The application of the theory in the offshore industry is rare, although Palmer (1999) used it. In the last decades trenching has been a practice where these theories can be applied and with the tendencies of working in deeper water and in arctic conditions it is useful to try to combine the knowledge from the dredging and the offshore industry regarding cutting processes. The cutting process in water saturated sand is dominated by the phenomenon of dilatancy. Due to shear stresses, the porosity of the sand increases, resulting in an absolute decrease of the pore water pressures. Since the soil stresses are a constant, and equal to the sum of the grain stresses and the pore water stresses, this implies that the grain stresses increase with decreasing pore water stresses. This results in much higher cutting forces. The decrease of the pore water stresses is limited by the water vapor pressure and so are the cutting forces. At shallow waters, the pore water may start to cavitate if the strain rates are high enough, but at very deep water this will probably not occur. In this paper the basics of the cutting theory are explained. This cutting theory however requires a lot of finite element calculations in order to determine the pore water pressures. The paper gives simplification that allows the user to apply the theory with the help of pre-calculated coefficients.

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Dynamic response of dry and water-saturated sand systems

Journal of Applied Physics ◽

10.1063/1.4990625 ◽

2017 ◽

Vol 122 (1) ◽

pp. 015901 ◽

Cited By ~ 6

Author(s):

J. W. LaJeunesse ◽

M. Hankin ◽

G. B. Kennedy ◽

D. K. Spaulding ◽

M. G. Schumaker ◽

...

Keyword(s):

Dynamic Response ◽

Saturated Sand ◽

Water Saturated

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The Bulldozer Effect When Cutting Water Saturated Sand

Volume 4: Offshore Geotechnics; Ronald W. Yeung Honoring Symposium on Offshore and Ship Hydrodynamics ◽

10.1115/omae2012-83296 ◽

2012 ◽

Author(s):

Sape A. Miedema

Keyword(s):

Saturated Sand ◽

Cutting Mechanism ◽

Tunnel Boring Machines ◽

Tunnel Boring ◽

Flow Type ◽

Cutting Angle ◽

Pore Pressures ◽

Boring Machines ◽

Water Saturated

In the last decennia a lot of research has been carried out into the cutting of water saturated sand at small cutting angles, especially at the Delft University and Deltares. Because of tunnel boring machines there was also interest in larger cutting angles in the 90’s. Now this can also be applied to the bulldozer effect in front of drag heads or the dragging of ice keels resulting in soil displacements under gouges. At small cutting angles the sand will flow over the blade according to the flow type of cutting mechanism, however at large angles a wedge will occur in front of the blade, while at very large cutting angles the sand will be pushed under the blade. Based on FEM calculations of the pore pressures a method has been developed named the parallel resistor method, in order to determine the pore pressures in the water saturated sand. Once these pore pressures are known, the forces and moments can be determined and it can be predicted at which cutting angle a static wedge will start to occur and at which cutting angle the sand will start to move under the blade resulting in much larger soil deformations. The paper will describe the model and also give a recipe on how to determine when the static wedge will occur.

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