Drainage and Filt
Drainage
and Filtration
Water is considered one of the chief contributors to the deterioration
of a pavement system, therefore, providing for the drainage, it is one of the
chief concerns in the designing of a system. The use of geotextile as part of a
drainage system is an instance where it can serve two functions of the same
time. When the fabric is used to wrap a pavement edge drain it allows water to
drain from the surrounding areas ,(26) while acting as a filter to
prevent fine particles being washed out from the subgrade into the road base
material under the effect of some unexpected loads (27) figure
(I-10) .Unusually , this load refers to a wheel load from some mode of
transport .The process of erosion of subgrades and the movement of soil
particles by water flow induced by a rapidly applied wheel load, is frequently
referred to as pumping. (22)
Pumping may occur when the stresses are applied to base course material
when the subgrade is a fine grained soil, and when the water is present at the
base course /subgrade interface. High stresses help the granular material at
the interface to deform the soft soil and causes it to form a slurry with
water. The excess pressure then cause the slurry to squirt up into the base
course. The fine suspended soil particles are deposited in the base course and
tend to fill its voids , thus decreasing its permeability and reducing its
shearing resistance. (22)
