Drainage and Filtr
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)
