Section of an Earth Dam : The design of an earth dam essentially consists of determining such a cross section the dam which when constructed with the available materials will fulfill its required tion with adequate safety. Thus there are two aspects of the design of an earth dam. b) Foundation pervious to a moderate depth, after which impervious strata isavailable : (c) Foundation pervious to a great depth: CASE 2 ONLY FINE GRAVEL OR COARSE SAND IS AVAILABLE PROVIDE DIAPHRAM TYPE DAM WITH SUITABLE ARRANGEMENTS CASE 3 ONLY SILT AND CLAY IS AVAILABLE NO CORE ONLY IMPERVIOUS BLANKED AND ROCK TOE PROVIDES SEEPAGE ANALYSIS ASSUMPTIONS FLOW IS – TWO DIMENTIONAL Soil is INCOMPRESSIBLE SOIL Soil is homogeneous and isotropic Soil is fully saturated Flow is steady Darcys law is valid Phreatic line – (seepage line) Line within the dam section having positive hydrostatic pressure at below section and negative hydrostatic pressure at above section Line has atmospheric pressure itself Separation line of saturated and non saturated portion Casagrande method of determining seepage line

1. C/S OF
DIFFERENT DAM
LAPLACE
EQUATION
DESIGN OF HYDRAULIC
STRUCTURE1/15/2014
PHREATIC LINE
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2. Case-1 : Gravel or coarse sand is available
along with clayey silt :
(a) Foundations impervious to a large
depth :
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3. b) Foundation pervious to a moderate
depth, after which impervious strata is
available :
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4. (c) Foundation pervious to a great depth
:
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5. CASE 2 ONLY FINE GRAVEL OR COARSE
SAND IS AVAILABLE
PROVIDE DIAPHRAM TYPE DAM WITH
SUITABLE ARRANGEMENTS
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6. • CASE 3
• ONLY SILT AND CLAY IS
AVAILABLE
• NO CORE
• ONLY IMPERVIOUS BLANKED
AND ROCK TOE PROVIDES
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7. SEEPAGE ANALYSIS
ASSUMPTIONS
FLOW IS – TWO DIMENTIONAL
Soil is INCOMPRESSIBLE SOIL
Soil is homogeneous and isotropic
Soil is fully saturated
Flow is steady
Darcys law is valid
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8. VZ + difference in VZ
dx
dz
Vx + difference in vx
VZ
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9. Phreatic line – (seepage line)
Line within the dam section
having positive hydrostatic
pressure at below section
and negative hydrostatic
pressure at above section
Line has atmospheric
pressure itself
Separation line of saturated
and non saturated portion
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10. Casagrande method of
determining seepage line
 locate start point of base
parabola at 0.3 L from
starting point
 locate focus F at starting of
drainge filter
C as a center and CF as
radious
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11.  cut the d/s slope and draw
vertical line through it which
will cut in filter as H
S is distance between FH
Mid of this FH is exit of
parabola.
Use base parabola equation
for determine another
points.
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12. Charactristics of phreatic
line
u/s slope at 90, less than 90
and greater 90
Runs at atmo. Pre.
In rock toe it emerges
vertically
Pervious foundation does
not influence
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