Unpaved roads (tem
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