Earthwork

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Earthwork

• Cross Section and Borrow Pit Methods

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• This lecture covers
• Readings 26-1 to 26-6, 26-8 to 26-10.
• Figures 26-1 to 26-4, 26-6, and 26-7
• Plate B-5 page 881, and B-2 page 878
• Examples26-1 and 26-3

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Volumes

• Usage
• Quantities of earthwork and concrete
• Capacities of some structures tanks,..
• Quantities of water discharged by streams per
  unit time
• Units
• 1 yd3 27ft3
• 1 m3 35.315ft3
• Acre-foot volume of an acre of 1 foot depth

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The Cross Section Method

• More accurate than a single profile along the
  centerline.
• Done by measuring cross sections (profiles) at a
  right angles to the centerline, usually at
  intervals of 50, or 100 ft.
• Readings at each cross section are taken at the
  centerline and at critical points perpendicular
  to the centerline.
• Cross sections are drawn and design templates are
  superimposed, the difference in area is the area
  of cut or fill at that section (end area).
• End areas can be cut, fill, or transition (both).
• Use the areas to compute volumes, knowing the
  distance between the sections.
• The whole work can be done with photogrammetry
  and a computer software, or a total station

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Data Recording

• Plate B-5
• Left page looks like Profile leveling, no
  intermediate points
• right page in front of each station, a group of
  fractions that describe the point location,
  reading, and elevation, in the form

Elevation rod reading distance from CL
99.2 7.4 52
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End Area Computation

• Simple cases formulae in fig 26-2, and fig26-4
• End areas by coordinates we will learn it
  through (traversing)

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End Area Computation

• Simple cases formulae in fig 27-2, and fig 27-4

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compute individual areas and add them up. After
computing the elevation at critical points, form
a table(mistakes!) station H L C D
E R G 2400 0 C12.5 C15.8 C18.0
C10.1 C12.2 0 15
15 33.8 20 0 33.3 15 Compute the
areas and add them up.
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Volume Computation

• Done after computing the end areas, identify
  which is cut and which is fill. Two main methods
• Average End Area Multiply the average area of
  the two sections by the distance between them.
  See next slide
• Ve A1 A2 L yd3
• 2 27

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• Prismoidal Formula
• What is a prismoid? A solid with parallel ends
  joined by a plane or continuously wrapped
  surfaces
• Fits most earthwork problems
• VP L(A14AMA2) yd3
• 627
• Where AM is the area of computed section midway
  between stations.
• Prismodial Formula is more accurate, The
  difference is called CP Prismoidal correction

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A2 0
Vp (h/6) S2 (4 S2/4) 0 (h/6)
2 S2 (h/3) S2
AM (S/2)2 S2/4
h
S/2
A1 S2
S
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Volume Computation

• Compute end areas at stations, fill the first
  three columns in table 26-3.
• Compute the cut and fill volumes, one of the
  formulae.
• Multiply the fill volumes by an expansion factor.
• Compute the amount of soil to be borrowed or
  transferred out of the site, which is the
  difference between the cut and the fill.

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Borrow-Pit Method

• Not suitable for linear features, very useful for
  construction sites.
• The site is divided into equal squares of sides
  20,50, or a 100 ft. Elevations are then measured
  at the corners of the grid, which are given
  titles that correspond to the coordinates of the
  corner in the grid, ex 3-D, 4-A,..
• V ? (hijn) A yd3
• 427
• The idea is to multiply each height by the number
  of complete squares it is common to.

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The volume of any square, or part of a square is
equal to the average height(elevation
difference) at the corners, times the area. To
compute the volume 1- draw a line between the
cut and the fill areas 2- compute the total
volume of all the complete cut squares, do the
same for the fill, use the previous formula 3-
Compute the incomplete squares separately and
add them to the squares. 4- Compute the
difference between the cut and the fill., pay
attention to the expansion factor.
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Site 1
Site 3
Site 2
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PROJECT 1Instructions
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B
A