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PGCIL DT Civil 2020 Official Paper

Option 3 : Subtractive

__Explanation:__

The volume of earthwork by trapezoidal method = V_{1}

V_{1} = \(common\: distance\left \{ \frac{First\: area + Last\: area}{2}+the \:sum \:of\: remaining \:area \right \}\)

The volume of earthwork by prismoidal formula = V_{2}

V_{2} = \(=\frac{Common\: distance}{3}\left \{ First\: area+ Last\: area + 2(Sum\: of odd\: area) + 4(Sum\: of even\: area)\right \}\)

**Prismoidal correction:**

- The volume by the prismoidal formula is more accurate than any other method
- But the trapezoidal method is more often used for calculating the volume of earthwork in the field.
- The difference between the volume computed by the trapezoidal formula and the prismoidal formula is known as a
**prismoidal correction.** **Since the trapezoidal formula always overestimates the volume, the prismoidal correction is always subtractive in nature is usually more than calculated by the prismoidal formula, therefore the prismoidal correction is generally subtractive.**- Volume by prismoidal formula = volume by the trapezoidal formula - prismoidal correction

**Prismoidal correction (C _{P})**

**\(C_{P}=\frac{DS}{6}\left \{ d- d_{1}\right \}^{2}\)**

Where, D = Distance between the sections, S (Horizontal) : 1 (Vertical) = Side slope, d and d_{1} are the depth of earthwork at the centerline