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Unformatted text preview: CE 563, Seepage & Slope Stability Handout #06 Page 1 of 5 CE 563, Seepage & Slope Stability Handout #06 Page 2 of 5 CE 563, Seepage & Slope Stability Handout #06 Page 3 of 5 CE 563, Seepage & Slope Stability Handout #06 EM 1110-2-1901
30 Sep 86
b. Guidelines for Flow Net Drawing. Once the section of porous media
and boundary conditions are determined, the flow net can be drawn following
(1) Determine flow conditions at the boundaries:
(a) Flow will be along and parallel to impermeable boundaries lines BCD
and FG, figure 4-5.
(b) Entrances and exits are equipotential lines, lines AB and DE,
figure 4-5, with flow perpendicular to them.
(c) Flow will be along and parallel to a line of seepage--line AB,
figure 4-6. Figure 4-6. Seepage through an embankment
underlain by an impermeable foundation
(courtesy of John Wiley and Sons
(d) Entrance and exit conditions for a line of seepage are shown in
figure 4-7 under "Conditions for Point of Discharge."
This will provide a feel for the flow net.
(2) Equipotential and flow lines must meet at right angles and make
curvilinear squares. Usually, it is best to make either the number of flow
channels a whole number (if the number of flow channels is a whole number, the
number of equipotential drops will likely be fractional).
(3) Generally, a crude flow net should first be completed and adjustments applied throughout the net rather than defining one portion since
refinement of a small portion tends to shift the whole net.
(4) The initial emphasis should be on getting intersections of flow
lines and equipotential lines at 90º, then shifting lines to form squares.
(5) If, in the finished flow net, either equipotential drops or flow
channels end up as a whole number plus a fractional line of squares (equipotential drop or flow channel), this should not be a problem but must be used
in any calculations based on the flow net. It is convenient to locate a partial equipotential drop in an area of uniform squares since this will make
accurate estimation of the fraction easier. 4-11
Page 4 of 5 CE 563, Seepage & Slope Stability Handout #06 FLOW NETS - Summary
ð 1. 2-D solution to differential
equation: ð 0 For anisotropic conditions, use
∗ 2. The seepage flow is given by: Equal drops between EPLs,
such that Δh = ΔH / Nd Δ All flow channels carry the
same volume of flow Δ / Δ and with squares, 1 Cannot touch each other
Flow lines will “sit” next to impervious zones
Flow lines start and finish (mostly?) Flow channels are like conduits Same volume of low through each flow channel (?) Connect points with equal TOTAL HEAD Cannot touch each other EPLs start and finish, typically at impervious lines First / last EPLs are at the entrance / exit locations EPLs and FLs intersect at 90 degrees TH = EH + PH Choose the datum for EH wisely Pore pressure, u = γw × PH 8. UPLIFT under dams Trial and error solution (requires patience) 7. PRESSURES Nf and Nd values do not have to be integers 6. HEADS Series of smooth lines offers a “better” solution 5. Equipotential lines Try to generate squares to meet the a = b criteria 4. Flow lines, flow channels 3. Drawing flow-nets γw = 9.81 kN/m3 or 62.4 lb/ft3 Distribution Total force calculation Sliding Factor of Safety, F = (N - U) μ / Hw (in units of length: meters, feet) (kPa, psf, etc.) Page 5 of 5 ...
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This note was uploaded on 02/03/2012 for the course CIVIL ENGI 563 taught by Professor Seepage during the Spring '11 term at Idaho.
- Spring '11