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ECIV 330 Soil Mechanics Chapter3 Permeability and Seepage

# ECIV 330 Soil Mechanics Chapter3 Permeability and Seepage -...

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ECIV 330 Soil Mechanics Prof. Bill X. Yu Spring, 2008

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Chapter III Permeability and Seepage Requirements Darcy’s law Hydraulic conductivity measurement and influence factors for hydraulic conductivity Flow net Quick sand condition Effective stress calculation Capillary phenomena
Background Why study seepage Estimating quantities of underground seepage Investigating problems involving pumping of water Stability analysis for earth dam and retaining-structures subjected to seepage force Contaminant transport Oil exploration etc

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Pavement Distress due to Water Prolem Moisture related problem accounts for more than 50% of pavement distresses a) Schematic of moisture migration in pavement; b) Example of moisture related damage Moisture infiltration Capillary rises Edge drain Pumping of fine materials due to excessive moisture accumulation (brown color) (a) (b) PCC/AC BASE SUBGRADE
3.1 Darcy’s Law Bernoulli’s Equation: Flow of Incompressible Fluid Flow is based on energy:

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Darcy’s Law Pressure, Elevation and Total Heads Consider a pipe filled with soil (e.g. sand) and water flowing through it under pressure. If a tube is vertically inserted into the pipe through a watertight hole (piezometer), the height that the water rises to in the tube is the pressure head. Change in Total Head
Darcy’s Law The elevation head , Z , is the vertical distance of a given point above or below a datum plane. All heads have units of length, e.g. meters, feet, etc. For flow of fluids in soil, velocities are quite small. Hence the velocity head is quite small and usually is ignored. Hence, the Eq. for Total Head becomes: Change in Total Head If measurements are made at two locations in the pipe, Bernoulli’s Equation may be written for each location. At each location, there is likely to be a different Total Head because of differences in Pressure Head and in Elevation Head.

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