Geofin Shallow Drainage
Geofin Shallow Drainage is a relatively new concept in
grassed area drainage that combines a slim polyethylene dimpled (cuspated) core and a geotextile
filter membrane. It is made in one size of 150mm deep x 25mm wide used for sports and turf
applications.
Design Flexibility, Ease of Installation, Efficient Drainage, Rapid reuse
The major benefits of Geofin Shallow Drainage for grassed areas are
its flexibility in design, its ease and speed of installation, its efficiency
and the fact that rapid re-use of the grassed area after installation is
achieved.
Geofin Shallow Drainage Core
Geofin Shallow Drainage is a strong yet light weight high density polyethylene sheet which specially
profiled cuspations that develop a much higher internal hydraulic gradient than pipe drains, thus
Geofin Shallow Drain can be laid with little or no gradient. Its design makes it a highly efficient
collector and transporter of water.
Geofin Shallow Drain Geotextile
Geofin Shallow Drain is supplied wrapped in a proven, selected
geotextile that eliminates blockage of the system and enhances
filtration. The surface area of the fabric is 80% permeable unlike
perforated pipes which are less than 5% permeable, thus water is
rapidly drawn from the soil into the drainage system.
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Back-Fill
There is no specific requirement for graded back fill due to the filtering characteristics of the geotextile
thus increasing the speed of installation and reducing costs. However, granular back fills are often
recommended to enhance surface water collection.
Sand can be used close to the surface without risk of injury to players and can provide a connection
to treatments such as sand top dressing, core and mini-rolling. When wetted into the trench and
consolidated the risk of settlement and rutting is minimised.
Geofin Shallow Drainage Installation
Being light Geofin Shallow Drain requires no specialised or
mechanical handling. On small or inaccessible areas Geofin can be
easily carried to site and installed manually. The narrow profile of
Geofin Shallow Drain also makes it ideally suited to installation in
conjunction with narrow trenching machinery which will produce
slits 35mm wide. Some of the advantages of using Geofin Shallow
Drain in narrow trenches include reduction in
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 Disruption to the surface
Excavated material and cart-away costs
Imported fill costs
Settlement over the trench
Time and labour requirements
Machinery size and therefore surface damage
Re-vegetation after installation
Geofin Shallow Drainage Jointing
Jointing Geofin is quick and easy and requires no special tools or skills.
Straight joints can be made by simply overlapping the core and taping
the geotextile. Connections to conventional pipes can be made via
purpose made prefabricated units.
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Geofin Shallow Drainage Design
Drainage problems and their solutions are diverse and therefore require careful design as well as
careful installation and maintenance. A good drainage design will produce major benefits to the end
user, such as
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Increased number of playing days (high utilisation)
Improved playing surface through rapid removal of water
Increased soil strength reducing treading damage
Promoting healthy plant growth
Promoting deeper root-take so reducing irrigation frequency in dry periods
Geofin flexibility in design, high levels of performance and ease of installation all help to promote the
benefits above in a cost-effective way.
A type of Geofin Shallow Drain is commonly used beneath block paving to collect and drain the sand
layer beneath the paving. When laid on impermeable substrate such as concrete, asphalt or roof
drainage, it is critical to remove the water where there is traffic to prevent saturation and therefore
deformation of paving structure.
Percolated water seeping the sand layer if unable to escape will
collect in the sand course layer. The permeability of paving sand
has a low permeability and will soon become saturated. Sealing
between block paving joints is soon damaged by sweeping and
traffic movement; there, no reliance on water resistant sealed joints
can be expected.
Should the sand layer 30-50mm become heavily saturated by
seepage between joints, the sand layer could liquefy and pump
through joints causing displacement and heave (elephants foot).
The solution would be to provide a positive drainage beneath the
sand. By using the single cuspated Shallow as a flat back with
geotextile wrapped geocomposite. Sand layer beneath block paved areas can be efficiently drained
increasing the life of the traffic zone.
Cooper Clarke Civils and Lintels, Bloomfield Road, Farnworth, Bolton, Lancashire.
Tel: 01204 862222 Fax: 01204 795296
A trading division of Buildbase Limited
Member of Grafton Group plc Registered in England No. 4725313
23 August 2007 Issue No4
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