Soil Compaction • Many civil engineering projects use soils as fill material, with soil normally being compacted to a dense state to ensure that it has the optimum properties. • Compaction on site is generally achieved by mechanical means such as rolling, ramming or vibrating. • Soil used as fill: v To refill an excavation or void v To provide made-up ground to support a structure v As a sub-base for a road, railway or airfield runway v As a structure; e. g. an earth dam
Applications of Compaction Improvement by compaction Ø Higher stability Ø Lower compressibilty Ø Lower permeability Ø Lower frost susceptibility Effect on mass of fill Ø Greater stability Ø Less settlement Ø Less deformation Ø Less water absorption Ø Less risk of frost heave Freezing
Theory of Compaction is the process of densification of soil by reducing air voids. The degree of compaction of a given soil is measured in terms of its dry density. The dry density is maximum at the optimum water content. A curve is drawn between the water content and the dry density to obtain the maximum dry density and the optimum water content. Dry density = M/V 1+w
Compaction curve Compaction Curve
Compaction Mould Collar Mould Base plate Rammer
Manual compacting Automatic compactors
Procedure Repeat 5 times Add H 2 O Fill with sand to 1/5 level H 2 O Compact by dropping rammer 25 times, & measure level Dry soil in oven to determine moisture content