PDF Experimental conceptualisation of the Flow Net system construction inside the body of homogeneous Earth Embankment Dams Dr Costas Sachpazis

In this case, the water in the upstream reservoir, with an initial head of 1.4 ft, causes a sand boil that quickly erodes beneath the dam and equalizes the water levels on both sides of the dam. A real-world example of failure because of leakage through an inadequate foundation is the Teton Dam (see, e.g., Rahn 1996). With a spreadsheet and the sand-tank model, students can build a simple finite-difference model drawing flow nets without working on special numerical modeling software. Also, the water balance can be better understood in a spreadsheet with the measured data in the lab. The groundwater model can be calibrated with the data from both piezometers and the discharge value collected by students. In this way, students feel a greater sense of investment in their learning after calibrating the model and using their own data.

For these cases, the distribution of Ksat and alpha must be known as well as the angle of anisotropy. For problems in the horizontal plane, water table gradients, saturated flow rates, and land slope gradients can be calculated. For land slope analysis, input the land elevation in place of the pressure head and set Ksat values equal to 1.0. The flownet in confined areas between parallel boundaries typically consists of elliptical and symmetrical flow lines and equipotential lines . Avoid abrupt changes between straight and curved flow and equipotential lines. For certain problems, portions of the flownet are enlarged, are not curvilinear squares, and do not satisfy Laplace’s equation.

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A Flow net is a graphical representation of flow of water through a soil mass. It is a curvilinear net formed by the combination of flow lines and equipotential lines. Properties and application of flow net are explained in this article. Uniform sand can be used in the sand tank for undergraduate laboratories, so that the material is isotropic. In this case, flow lines and potentiometric contours meet each other at right angles. Normally a flow net is drawn with squares that are defined by the intersections of flow lines and potentiometric contours.

• There are two major techniques for solving Laplace’s equation.
• All the approaches above are aimed at emphasizing fundamental knowledge and stimulating student engagement.
• It is only applied to problems with simple and ideal boundaries conditions.
• The space enclosed between two adjacent flow lines and two successive equipotential lines in called a field.
• Trop et al. introduced a short field trip for observing outcrops and extent of aquifer rocks, which gives students a greater understanding of an entire aquifer.

The uplift pressure at any point within the soil mass can be found using the undermentioned formula. Equal quantity of seepage occurs in each flow channel. The second flow net pictured here (modified from Ferris, et al., 1962) shows a flow net being used to analyze map-view flow , rather than a cross-section. Note that this problem has symmetry, and only the left or right portions of it needed to have been done. To create a flow net to a point sink , there must be a recharge boundary nearby to provide water and allow a steady-state flowfield to develop.

velocity potential. The electric current is analogus to the velocity of flow

The uniform nature of the sand makes it suitable for the sand-tank model. Figure2 is a photomicrograph of sand grains from the St. Peter Sandstone . Part of the sand-tank laboratory can involve a binocular microscope that is set up for students to observe the sand grains and make inferences about the environment of deposition. In an earlier laboratory exercise, the same sand can be used in a permeameter for determination of hydraulic conductivity, which can be compared to the value determined in the sand-tank and flow-net laboratory exercise. The graphical method is most extensively used method among the methods stated above. The graphical method of flow net construction involves sketching by trial and error.

There is a high demand for groundwater instruction because of strong employment prospects for trained hydrogeologists and the growing recognition of groundwater in other fields such as water resources and biology. For example, an article published in Science indicates the strong demand for hydrogeologists. Department of Labor and the American Geological Institute , the job market for groundwater specialists is growing . The space between five adjacent flow lines is called a flow channel. Following properties of flow net are considered before preceding for construction and application of flow nets.Flow lines and equipotential lines cut each other at right angles i.e., they are mutually orthogonal. Let the head of water stored by the dam is H Then upstream ground surface represents equipotential line with 100% head.

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The flow lines must start and end at right angles to the ground surface upstream and downstream respectively. We can also attempt to replicate the flow through the actual structure using physical models. There are two major techniques for solving Laplace’s equation. The first is an approximation known as flownet sketching, and the second is the finite difference method.

• Darrel D. Sipe built the sand-tank model used in most of the photos in this paper, as part of a special topics course while he was a graduate student at South Dakota School of Mines and Technology.
• Weirs designed and constructed on the basis of Bligh’s theory also failed due to undermining of the subsoil.
• For these cases, the distribution of Ksat and alpha must be known as well as the angle of anisotropy.
• The space between any two adjacent flow lines is called flow channel.
• Students can visualize the dye’s migration in response to the hydraulic gradient, which leads to a greater understanding of advective-dispersion transport processes in the aquifer (see Fig.4).

An equipotential line cannot intersect another equipotential line. It is only applied to problems with simple and ideal boundaries conditions. • Flow net should not be governed by the gravity force to maintain the fixed pattern of flow net.

The well on the upgradient side shows a water level that is lower than the reservoir level on the left side of the tank, which helps students visualize the head in the sand at that point where it is measured. A small amount of liquid dye added to the glass tube can make this water level easier to see. The well on the downgradient side shows a water level that is higher than the reservoir level on the right side of the tank (Fig.1), which helps students understand an upward gradient. In some field situations similar to this, a flowing artesian well can be obtained with a sand-point well near a stream where the hydraulic gradient is upward. Students often are surprised when they learn that the discharge through each flow tube is equal in the flow net. In this way, students gain a deeper understanding of Darcy’s law.

Students learn from the sand tank through interaction and visualization, and by collecting and interpreting data. This integrates the theories from lectures into the sand-tank laboratories, enhancing students’ skills and understanding. This document describes the necessary input and interpretation of the output for the program FLOWNET. FLOWNET is a simple computer program developed to calculate hydraulic and topographic gradients for two-dimensional surfaces. Flow rates are calculated for saturated and unsaturated conditions based upon application of Darcy’s law and the exponential hydraulic conductivity equation.

Flow Net – Properties and Applications

The flownet sketching technique is straightforward and adaptable, and it represents the flow regime. It is the preferred method of analysing flow through soils for geotechnical engineers. Before delving into these solution techniques, however, we will establish a few key conditions necessary to comprehend two-dimensional flow. An equivalent amount of flow is passing through each streamtube , therefore narrow streamtubes are located where there is more flow. The smallest squares in a flow net are located at points where the flow is concentrated , and high flow at the land surface is often what the civil engineer is trying to avoid, being concerned about piping or dam failure.