Unpaved roads (te
Unpaved
roads (temporary roads)
Unpaved roads ,sometimes referred to as temporary roads ,are frequently
required to give site access weak bearing soils such as soft clays , water
bearing silts or peats . Even with the stronger clay formations, trafficking
can become difficult during and after wet weather . (18)
Before the advent of geotextiles, this problem was overcome by placing
a carpet of aggregate directly on the weak formation to a sufficient depth to
spread vehicle wheel loads to such an extent that they do not overstress the
weak formation .(9) Despite this , it was found that extensive ruts
were formed on the surface of such unpaved roads along the paths of the
vehicles’ wheels . These surface ruts have reflected at depth in the surface of
the weak formation where the granular fill tends to punch into the soft soil
and become ineffective (18) . The dynamic nature of this loading can
also cause fine soil to be pumped upwards into the aggregate sub-base . Also
the finer granular constituents of the sub-base can be washed out or downwards
by the action of rainfall and drainage through the road sub-base aggregate .
Heavy compaction of an unpaved road during construction can have a very similar
effect to vehicle loading.
These problems have been minimized by incorporating a suitable
geotextile between the sub-base and subgrade in order to distribute the normal bearing capacity of the road. (9)
Geotextiles
act as a reinforcing element as well as a separator, which prevents the rich
aggregate of the sub- base from mixing with poor soil of subgrade , thereby
helping in retaining the integrity of sub- base . Therefore , less thickness
sub-base is sufficient for the same strength and performance . Thus application
of geotextile not only increases the life of structure with better
serviceability but also generates an economy equivalent to the cost of sub-
base material saved including its labour and transportation costs. (2)
