Paved roads (perma
Paved roads (permanent roads)
In the case of paved roads , any design resulting in rutting type deflections of the surface would obviously be unaccepted .
The difference between paved and unpaved road applications is highlighted by the fact that the maximum strain induced in a geotextile at the base of an unpaved road can be
Fig (I-12) Use of geotextiles in temporary road construction
in the region of 5-15% , whereas that in an asphalt pavement is likely to be in the region of 0.04 to 0.08% . This is due to the fact that the tolerable deformation of a paved road is considerably less than that of an unpaved road. (9)
The lower layers in a permanent road pavement generally comprise granular materials which are used to form the sub-base . If the sub-base is a cohesive soil, it may be necessary to employ a capping layer to give a sound formation on which to place and compact the sub-base . Although the road may be constructed successfully , the long term interaction between a cohesive sub-grade and the unbound granular layers placed on it, can have a dramatic effect on the design life of the entire pavement.
Road pavements are rarely impermeable : water can enter the road construction and come finally to rest near the surface of subgrade where it can cause softening of the soil. When this water is put under pressure by dynamic traffic loading , high water pressure are induced that can jet or pump the softened formation soil into the granular layers above . As well as reducing the support offered to the sub-base , this can lead to a reduction in permeability and dynamic deformation modulus of the unbound layers, leading to premature failure of the pavement. Such problems can be ameliorated by the use of a suitable geotextile which will tend to inhibit pumping. (18)
Geotextiles can be usefully employed at three different locations in a permanent road. At the interface between the aggregate sub-base and the subgrade soil, within the pavement structure , or with a surface overlay.
