Earthworks ~ this will involve the removal of topsoil together with
any vegetation, scraping and grading the required area down to
formation level plus the formation of any cuttings or
embankments. Suitable plant for these operations would be tractor
shovels fitted with a 4 in 1 bucket (page 174): graders (page 173)
and bulldozers (page 171). The soil immediately below the
formation level is called the subgrade whose strength will generally
decrease as its moisture content rises therefore if it is to be left
exposed for any length of time protection may be required.
Subgrade protection may take the form of a covering of medium
gauge plastic sheeting with 300 mm laps or alternatively a
covering of sprayed bituminous binder with a sand topping applied
at a rate of 1 litre per m^2. To preserve the strength and durability
of the subgrade it may be necessary to install cut off subsoil
drains alongside the proposed road (see Road Drainage on page
752).
Paving Construction ~ once the subgrade has been prepared and
any drainage or other buried services installed the construction of
the paving can be undertaken. Paved surfaces can be either flexible
or rigid in format. Flexible or bound surfaces are formed of
materials applied in layers directly over the subgrade whereas rigid
pavings consist of a concrete slab resting on a granular base (see
pages 134 & 135).
Road Construction