Design techniques for geocomposite drainage products for vertical and horizontal drainage

1. Design techniques for geocomposite drains
1. Determine the required discharge of groundwater at the base of a wall or
the seepage flow per m2 into the drain layer of roof garden in a horizontal
application by either:
a) Use of a combination of flow net, soilpermeability and hydrological
information
b) Relate to equivalent gravel drainage layer;
Kv gravel = 10-3 m/s => 0.3 m gravel column = 0.3 l/s.m
c) Refer to German Standard DIN 4095; gives detailed information on drainage to
structures
Seepage in vertical plane = 0.3 l/s.m
Seepage in horizontal plane = 0.03 l/m2
Under foundation slabs = 0.005 l/m2
2. Calculate maximum active earth pressure on Enkadrain;
For vertical wall Pa = Ύ• ka • h kPa
For horizontal roof Pa = Ύ• h kPa
Ύ = weight of soil kN/m3
ka = coefficient of active earth pressure
h = height of wall or soil thickness
3. Compare required
discharge capacity with
specific geocomposite
product specification
see next page
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2. Example (vertical)
• Vertical wall 8 m high
• Soil unit weight ( Ύ) 20 kN/m3
• Required drain capacity – DIN 4095 is 0.3 l/s.m
• Coefficient of active earth pressure ka = 0.4
Pa = 20 x 0.4 x 8 = 64 kPa
As an example we took the product called Enkadrain and get the below figures
from the brochure, it can be done for many types of geocomposite drainage
sheets.
For a certain type of Enkadrain at 64 kPa the discharge capacity is:
64-50
interpolation 0,47- [ ---------- x (0,47-0,19) ] = 0,39 l/s.m
100-50
Enkadrain (chosen geocomposite sheet drain) is =
0,39
------ = 1.3 times more permeable than required
0,3
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3. Example (horizontal)
• Roof garden hydraulic gradient equals 1% over 10 m drain length
• Soil cover 0.4 m with unit weight of 18 kN/m3
• Rainfall 20 mm in one hour. 20 mm/hr = 20 l/hr.m2 = 0.0055 l/s.m2
• Over 10 m drain length = 10 x 0.0055 = 0.055 l/s.m
P = 0.4 x 18 = 7.2 kPa
For a certain type of Enkadrain at 7.2 kPa the discharge capacity is:
7,2-5
Interpolation Q0.01, 7.2 kPa = 0.34 – [ -------- x (0.34 – 0.18) ] = 0.27 l/s.m
10-5
Discharge capacity of the chosen geocomposite drain is =
0,27
---------- = 4.9 times higher than required
0,055
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4. Required discharge capacities
Vertical applications
• To be determined in accordance with local standards and conditions.
• Indication: required discharge capacity per running meter of wall in
accordance with DIN 4095:
Types of soils and water flows Discharge in
l/(s·m)
Soils with sheet flows or accumulated water; 0,10-0,30
Little surface water
Low permeable soils with infiltrated water; 0,05 – 0,10
No surface water
Very low permeable soils; < 0,05
No accumulated or surface water
Horizontal applications
• To be determined in accordance with local standards and conditions.
• Indication: required discharge capacity roof gardens per m2 roof area in
accordance with DIN 4095:
Safe general rule: q = 0.03 l/(s·m2)
Drainage under concrete foundation slabs:
safe general rule: q = 0.005 l/(s·m2)
The technical data and information set forth in this paper/slideshow reflect our best knowledge at the time
of issue. The slideshow is subject to changes pursuant to new developments and findings, and a similar
reservation applies to the properties of the products described. We do not undertake any liability for results
by usage of these products and information. We do not take any responsibilities. This slideshow is only for
general information.
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