Computation of Earth Work from Spot Levels

This method is used for the elevations of basements to calculate volume of earth work, large tanks and borrow pits. The whole area is divided into a number of rectangles or triangles in this method as shown in figure. The levels are taken at corner points before and also after excavation. At each corner point the depth of excavation is measured. Then for each simple figure (rectangle or triangle)

V = Area of the figure × average depth.

Therefore for a rectangle with corner depth h_a, h_b, h_c and h_d,

For a triangle,

when all volumes is added give total volume of work.

 It may be noted that in Fig. (a), in total volume calculations depth of some corners appear once, some twice, some of them three times and some four times. If

Σh₁ = some of depths used once

 Σh₂ = sum of depths used twice

Σh₃ = sum of depths used thrice

Σh₄ = sum of depths used four times.

 Then

Similarly in figure 2, sum depths are used once, some two times, some three times and some others six times. Defining h_i same as above.