Estimating Sheet

# How to estimate earthwork volume through contour map

Construction Software In this construction video tutorial, detail explanation is given on how to work out the earth work or earth volume with contour map. Besides, one can learn how to compute water quantity in a pond or reservoir or any other water preservation.

For this purpose, the following two methods are used.

method#1: Trapezoidal Formula:-
volume =V= D (Ao + An /2 ) +(A1 + A2 + A3 + …………An-1)
where,
V stands for volume of earth or water.
D stands for contour interval.
Ao stands for area of first contour.
An stands for Area of last contour.
A1, A2, A3… stand for Areas of remaining contours.

method#2:Prismoidal Formula:-
Volume =V= D /3 (Ao + An) + 4(A1 + A3 + A5……) + 2(A2 + A4 + A6……)
Where,
V stands for volume of earth or water.
D stands for contour interval.
Ao stands for Area of first contour.
An stands for Area of last contour.
A1, A3, A5 stands for areas of odd contours
A2, A4, A6 stands for areas of even contours

Here, the solution is given for the following problem :-
Given below, the area of various contours in a reservoir :-

Contour - Area in m2
670 - 2000
671 - 10650
672 - 12400
673 - 12630
674 - 15320
675 - 18160

Solution : Applying Trapezoidal formula :-

V= D (Ao + An /2 ) +(A1 + A2 + A3 + …………An-1) (D denotes the difference among contour areas)
V = 1(2000 + 18160)/2 [ summation of first and last contour areas] +10650+12400+12630+15320 [sum of the remaining contour areas.

V = 61080 m3 (volume of water in reservoir)

To learn how Prismoidal Formula is used, watch the following video tutorial.

Video Source: SL Khan 