Civil and Environmental Applications of Geosynthetics - Reinforced Soil Engineering: Advances in Research and Practice - page 7

Figure 3 Geocomposite.
hydraulic conductivity to account for the turbulent flow. Because of the large
normal stress acting on the plane of geonet/geocomposites, the crushing strength
of the core has to be assessed. Geocomposites are sometimes tested with site-
specific soils and liquid. A reduction in the flow rate is expected because of the
intrusion of the geotextiles into the core. It is also important to ensure that
geotextile sheets, if installed along the slope, do not delaminate from the geonets
due to shear stress, because geocomposites are installed at a gradient to allow for
gravity flow. The drainage systems of a geocomposite are usually constructed for
allowance of cleaning by flushing because they are normally subject to biological
action.
3.4 Separation and Reinforcement in Roadways
In the unpaved roads and railways, geotextile separates the subgrade and
stonebase/ballast (Fig. 4) . The California bearing ratio (CBR) of the soil subgrade
may be used to determine if an unpaved road should be designed for separation or
for separation and reinforcement. The intrusion of stone aggregates into the soil
subgrade is prevented by the geotextile in a roadway. In a railway, the fine soil
particles are stopped from pumping into the stone aggregates. In addition to
tensile strength, other mechanical properties of geotextiles, such as resistance to
burst, tear, impact, and puncture, are used for designing geotextiles as a separator.
However, existing practice does not emphasize design when geotextiles are used
as a separator compared to reinforcement and drainage applications.
For unpaved roadways, the use of geotextile reinforcement results in cost
savings because the thickness of stone aggregates may be reduced. In paved
roads, the geotextiles may prevent reflective cracking. The geotextile or biaxial
geogrids may be placed above the cracked old pavement followed by the asphalt
overlays. The life of the overlay is prolonged in the presence of geosynthetic
materials, or a reduced thickness of overlay may be used while keeping the
lifetime equivalent to the case without using the geotextile. In addition to
preventing reflective cracking, the geosynthetic reinforces the asphalt pavement.