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## Earthwork

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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 • 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: 99.2 7.4 52 Elevation rod reading distance from CL**End 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 G 24+00 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.**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**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(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. ( )**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.**Site 1**Site 3 Site 2**Assumed 36 for piles**200 ft**C**D B A