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J CEE 120-Water in soils 2

# J CEE 120-Water in soils 2 - Chapter 7 Water in soils 2...

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Chapter 7 Water in soils, 2: Permeability, Seepage, Effective Stress The importance in civil engineering of water in soils is mentioned at the beginning of previous Chapter 6, Water in Soils 1. Most geotechnical engineering problems somehow have water associated with them in various ways. “Static” soil-water problems: - Capillarity - Shrinkage - Swelling - Frost action - Ground water pressure – effective stress concept “Dynamic” soil-water problems: When watar flows through soil – however this flow is usually very slow so dynamic is not the best word to describe it

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Dynamics of Fluid Flow There are several different ways to describe or classify fluid flow: Steady - corresponds to conditions that are constant with time Unsteady - corresponds to conditions that vary with time One-dimensional - all the fluid parameters such as pressure, velocity, temperature, etc., are constant in any cross section perpendicular to the direction of flow (however, these parameters can vary from section to section along the direction of flow) Two-dimensional - the fluid parameters are the same in parallel planes Three-dimensional - the fluid parameters vary in the three coordinate directions In reality, flow through soil is practically always three-dimensional . However, for practical purposes of analysis, flow problems in geotech-nical engineering are usually assumed to be either one- or two- dimensional . This assumptions are adequate for most practical cases. Because density changes can be neglected at ordinary stress levels for most geotechnical engineering applications, flow of water in soils can be considered incompressible. Flow can also be described as: Laminar, where the fluid flows in parallel layers without mixing, or Turbulent, where random velocity fluctuations result in mixing of the fluid and internal energy dissipation.
Let u examine flow of water under a sheet pile wall. Water slowly flows from left side of the wall to the right. The arrows indicate direction of flow. The flow is obviously from left to right side because water elevation on the left side is higher. We can picture a flow between points 1 and 2 as a flow through a pipe. If the water levels are maintained at both sides, this flow is obviously steady state , slow and laminar because water is not mixing but flowing in orderly fashion in parallel layers.

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We can describe this flow by well-known Bernoulli energy equation for incompressible steady flow of a fluid through a pipe written in terms of energy per unit weight : Whether the flow is in pipes, open channels, or through porous media, there are energy or head losses associated with the fluid flow . To compare total heads h 1 and h 2 at points 1 and 2, an energy or head loss term h f must is added to h 2 . The equation states that the
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J CEE 120-Water in soils 2 - Chapter 7 Water in soils 2...

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