Question

The initial decrease of dry density at lower water content is exhibited in ____________ type of soil.

(a) Fine grained soil

(b) Black cotton soil

(c) Alluvial soil

(d) Cohesion soil

This question was addressed to me during an internship interview.

The doubt is from Factors Affecting Compaction topic in section Compaction of Geotechnical Engineering I

Answer 1

The correct option is (b) Black cotton soil

Easy explanation: The initial decrease of dry density at lower water content is a characteristic feature of black cotton soils, high swelling clays and fat clays. The optimum water content for such soils ranges between 20 to 25%.