P(x,y)dy

dx

y

x

x

y

L

H

LHkQHkLQykxQ

dyykdxQdyykdxQydxdykQ

yAAdxdykQ

dxdykv

H

L

H

L

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222

1..

2202

0

0

0

GeocompositeDrainageor Granular soil

Soil

Asphalt

The value of Q refers to flow capacity of system and using this resultit is possible to obtain the discharge admissible value of thegeocomposite drain in relation to granular material

e GMGMGM AikQ = Considering i = 1 (vertical drainage)

kGM Permeability coefficient of granular materialAGM Cross section area

Lets suppose a granular material drain with 20cm width

1,00m

20,0== GMGMGMGM kAikQConsidering smkGM /15,0= we have msmQGM //03,020,015,0 ==Now, comparing the QGM result with admissible flow capacity of MacDrain

Flow capacity of MacDrain for 100kPa and hydraulic gradient unit,we have QMacDrain = 0,41m/s/mIf we consider a range of 30cm to MacDrain, we will have0,123m/s/mand if we adopt a safe factor of SF = 2, we will have0,0615m/s/m.Then, the final result is two times higher than the result obtained forthe granular material.

0,0615m/s/m > 0,03m/s/m