Filter Sheet Drains provide a cost effective option to the conventional use of aggregate where large surface areas require drainage. Geosynthetics Australia’s dimpled plastic sheet drains provide effective drainage and waterproof membrane protection on foundation walls and other underground structures. They are widely used for vertical or horizontal drainage on piled structures, retaining walls, tunnel drainage, podium decks and soil bank stabilization. They alleviate the hydrostatic pressure behind walls and the potential for structural failure.
Filter fabric sheet drains are a composite geosynthetic made from a high quality, abrasion resistant, non-woven polyester geotextile filter fabric that is bonded to an impermeable HDPE cuspated core. Both polymers are inert to a wide range of acids and alkalis common in a soil environment.
Retaining Wall Drainage
Almost 80 percent of retaining walls fail at some point due to improper drainage. To avoid this an effective drainage system should be installed behind the structure. Whilst it can be difficult to accurately calculate seepage through non homogeneous soils, GA sheet drains ensure that the permittivity into the core and the in-plane flow rate remain constant. Dimple sheet drains deliver superior drainage to traditional materials such as crushed aggregate and conventional pipe systems. Moreover they are lightweight, easy to handle and install, require minimal trench excavation and resist loads from infill and formwork.
Geocomposite drains are installed with the geotextile facing the soil and the HDPE sheet up against the wall. The geotextile fabric prevents soil or sand particles from entering the three dimensional dimpled core and creates an air gap so that the wall can breathe and seepage condensates outward onto the plastic membrane. The moisture then falls to a footing drain where it is removed. The air gap helps to keep cement block walls dry and mould and fungi from growing on the wall.
Because of their high compressive strength, geocomposite sheet drains can be cast into the final concrete face or alternatively sprayed concrete can be applied on the surface to create the final finish. The HDPE cuspated drainage core provides an excellent bond with shotcrete. Filter fabric sheet drains can also be used as replacement for a no-fines concrete layer.
The prefabricated drainage system provides 3 primary benefits:
• Quickly removes water from behind the wall, relieving hydrostatic head pressure
• Provides a channel to take the water down to the collection system
• Protects the waterproofing, especially during backfilling
Waterproofing Membrane Protection
GA Geocomposite Sheet Drains also protect waterproofing material for both horizontal and vertical tanking applications. This eliminates the cost of a separate protection board. During backfilling or landscaping the stiff plastic sheet protects waterproofing membranes from sharp stones, traffic from on-site workers and tools from construction trades. Cuspated Sheet Drains also act as a thermal insulation barrier adjacent to the waterproofing membrane. They can be applied to concrete block work and highly textured surfaces.
Road and Rail Tunnel Drainage
Because of the variation in permeability and grain size, the velocity of seeping water through porous media varies greatly (Darcy’s Law). GA Geocomposite Sheet Drain is designed to collect and drain large volumes of unwanted surface and groundwater from road and rail tunnels. Its high strength withstands ground pressures and the compaction forces of wet concrete. When connected to a tunnel drainage discharge system GA Sheet Drain maintains a high water flow and eliminates hydrostatic build-up against the structure.
The GA Filter Sheet Drain also protects the waterproofing membrane from damage. The dimpled drainage core creates an air void to isolate the structure from the effects of the surrounding ground.
Tunnel Invert Drain
Invert sheet drains are highly flexible, cuspated HDPE, waterproof geomembranes that also minimise the build-up of hydrostatic pressure, thus protecting and enhancing the integrity of a road or rail tunnel.
When filled with concrete the inverted sheet drains provide a free draining void behind tunnel waterproofing or basement floors. The tunnel drainage layer collects infiltration water from the walls, reduces hydrostatic pressure and enhances the effectiveness of the waterproofing. Inverted sheet drain can also be used as a gas collection void under a reinforced concrete slab.
The open flow channels in the cuspated core deliver high flow velocities, which, together with the smooth HDPE surface, makes invert sheet drains extremely resistant to clogging by precipitates.
Cuspated invert sheet drains are easily attached to the excavated wall of the tunnel or onto a shotcrete smoothing layer with spider fixings screwed onto soil nails. When used to waterproof basement slabs or act as a gas collection barrier, the dimples are laid face down on a separation layer and a cement grout is poured on top. Because sheet drains are flexible, they follow the contours of excavated tunnel walls. Shotcrete adheres directly to the inverted surface of the liner. The rebound loss is significantly reduced in comparison to smooth waterproof linings as concrete is retained in the dimples.
Podium decks and rooftop gardens
Podium decks and roof gardens are an easy way to create extra living space in places that offer private or public access. They also have environmental benefits, such as reducing the heat island effect of cities, and the load on stormwater systems during heavy rain.
Natural and artificial grass, concrete and natural stone pavements are usually installed on roof tops, balconies and podium decks. To maintain the integrity of the surrounding structure, a light weight drainage system, specifically designed for this purpose, should be installed to cover the entire area.
Geosynthetics Australia’s 18mm high double cuspated sheet filter drain performs a multi-faceted role by providing protection for waterproofing systems and collecting excess water in plaza decks, split slabs, planters, roof top gardens, and other horizontal surfaces. Planting soil is retained while allowing water to pass into the drainage core. The collected water is then conveyed to a proper collection system.
GA sheet drains are available in rolls 1.1m x 20m. For larger applications sheet drains are available in widths up to 2.2 metres, with or without a filter fabric. Dimple heights ranging from 10mm to 30mm are available for various applications.
When used with retaining walls, drainage geocomposites are installed either vertically (retaining walls) or horizontally (podium decks) with the geotextile facing towards the soil and the geomembrane against the wall. During backfilling with free draining fill, sheet drains are held in place by either taping, nailing, gluing or hanging over the wall. It is important not to disturb or damage the filter fabric during this process. For wider areas, the dimples along the edges of the sheets press together or butted edge to edge and sealed with reinforced tape.
|Core Properties||Units||10 Single||20 Single||18 Double||Geotextile Properties|
|Compression (ASTM-1621)||kPa||500||200||250||Flow||>200 l/m2/s|
|Flow||l/min/m width||223||480||450||EOS||<0.12 mm|
|Roll length||m||30||30||30||Grab||>500 N|