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Earthwork. Cross Section and Borrow Pit Methods. 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 893, and B-2 page 890 Examples:26-1 and 26-3. Volumes. Usage: Quantities of earthwork and concrete
EarthworkCross Section and Borrow Pit MethodsThis 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 893, and B-2 page 890
  • Examples:26-1 and 26-3
  • 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
  • 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.
  • 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:
  • 99.27.452Elevationrod readingdistance from CLEnd Area Computation
  • Simple cases: formulae in fig 26-2, and fig26-4
  • End areas by coordinates: we will learn it through (traversing)
  • End Area Computation
  • Simple cases: formulae in fig 27-2, and fig 27-4
  • 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 G24+00 0 C12.5 C15.8 C18.0 C10.1 C12.2 0 15 15 33.8 20 0 33.3 15Compute the areas and add them up.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 27Prismoidal Formula
  • What is a prismoid? A solid with parallel ends joined by a plane or continuously wrapped surfaces
  • Fits most earthwork problems
  • VP = L(A1+4AM+A2) yd3
  • 6*27
  • Where AM is the area of computed section midway between stations.
  • Prismodial Formula is more accurate, The difference is called CP: Prismoidal correction
  • 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.
  • 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
  • 4*27
  • The idea is to multiply each height by the number of complete squares it is common to.
  • ()Plate B.2The 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 areas2- compute the total volume of all the complete cut squares, do the same for the fill, use the previous formula3- 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.Site 1Site 3Site 2PROJECT 1Instructions36Assumed 36 for piles200 ft20CDBA
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