Example: A soil in the borrow pit is at a dry density of 17 kN/ m³ with a moisture content of 10%. The soil is excavated from this pit and compacted in a embankment to a dry density of 18 kN/ m³ with a moisture content of 15%. Compute the quantity of soil to be excavated from the borrow pit and the amount of water to be added for 100 m³ of compacted soil in the embankment.
Ans :Volume of compacted soil = 100 m³ & Dry density of compacted soil = 18 kN/m3
Weight of compacted dry soil = 100 × 18 = 1800 kN. This is the weight of dry soil to be excavated from the borrow pit.
Weight of wet soil to be excavated = 1800 (1 + w) = 1800 (1 + 0.10) = 1980 kN.
Wet density of soil in the borrow pit = 17 (1 + 0.10) = 18.7 kN/ m³
Volume of wet soil to be excavated = 1980 / 18.7 = 105.9 m³
Moisture present in the wet soil, in the borrow pit for every 100 m³ of compacted soil
= 1800 × 0.10 = 180 kN
Moisture present in the compacted soil of 100 m³ = 1800 × 0.15 = 270 kN
Weight of water to be added for 100 m³ of compacted soil = (270 – 180) kN = 90 kN
= 90/ 9.81 m³ = 9.18 kl
