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# Earthwork - PowerPoint PPT Presentation

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

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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

• 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

• 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).

• 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

distance from CL

• Simple cases: formulae in fig 26-2, and fig26-4

• End areas by coordinates: we will learn it through (traversing)

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

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.

• 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 the

• 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

• 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.

• 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.

(

)

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 the average

Site 3

Site 2

PROJECT 1 the average Instructions

36 the average

Assumed 36 for piles the average

200 ft

20 the average

C the average

D

B

A