The wide range of soil types available as highway
construction materials have made it obligatory on the part of the highway
engineer to identify and classify different soils. A survey of locally
available materials and soil types conducted in India revealed wide variety of
soil types, gravel, moorum and naturally occurring soft aggregates, which can
be used in road construction. Broadly, the soil types ca n be cat egorized as
red soil, Desert sands, Alluvial soil, Clay including Black cotton soil.
standard grain size soil
Gravel: These are coarse materials with particle size under
2.36 mm with little or no fines contributing to cohesion of materials.
Moorum: These are products of decomposition and weathering of
the pavement rock. Visually these are similar to gravel except presence of
higher content of fines.
Silts: These are finer than sand, brighter in color as
compared to clay, and exhibit little cohesion. When a lump of silty soil mixed
with water, alternately squeezed and tapped a shiny surface makes its
appearance, thus dilatancy is a specific property of such soil.
These are finer than silts. Clayey soils exhibit stickiness, high strength when
dry, and show no dilatancy. Black cotton soil and other expansive clays exhibit
swelling and shrinkage properties. Paste of clay with water when rubbed in
between fingers leaves stain, which is not observed for silts.