Embankment lecture 4

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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 is available :
(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

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Embankment lecture 4

  1. 1. C/S OF DIFFERENT DAM LAPLACE EQUATION DESIGN OF HYDRAULIC STRUCTURE1/15/2014 PHREATIC LINE 1/15/2014 1
  2. 2. Case-1 : Gravel or coarse sand is available along with clayey silt : (a) Foundations impervious to a large depth : 1/15/2014 2
  3. 3. b) Foundation pervious to a moderate depth, after which impervious strata is available : 1/15/2014 3
  4. 4. (c) Foundation pervious to a great depth : 1/15/2014 4
  5. 5. CASE 2 ONLY FINE GRAVEL OR COARSE SAND IS AVAILABLE PROVIDE DIAPHRAM TYPE DAM WITH SUITABLE ARRANGEMENTS 1/15/2014 5
  6. 6. • CASE 3 • ONLY SILT AND CLAY IS AVAILABLE • NO CORE • ONLY IMPERVIOUS BLANKED AND ROCK TOE PROVIDES 1/15/2014 6
  7. 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 1/15/2014 7
  8. 8. VZ + difference in VZ dx dz Vx + difference in vx VZ 1/15/2014 8
  9. 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 1/15/2014 9
  10. 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 1/15/2014 10
  11. 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. 1/15/2014 11
  12. 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 1/15/2014 12

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