April 2018 saw the commencement of a special maintenance project in the Eastern Cape, South Africa, where over 100 000 metres of Kaytech’s Geocomposite Megaflo Panel Drain System was used. This 30-month long upgrade project by SANRAL (South African National Roads Association Limited) required construction of approximately 100 km of subsoil drains, to be installed directly along the edge of the existing sealed road surface, on Provincial Route R56 Section 6: Indwe to Elliot and Section 7: Elliot to Maclear.
Due to limited working space as well as the urgent need to drain the road prism and preserve the layers, contractor, Tau Pele Construction, investigated alternatives to conventional drainage construction. Kaytech representative, Julian Maastrecht gave his assurance that, “using this unique drainage system will not only reduce installation time, but will eliminate the need for 19 mm stone aggregate”. Using a Ditch Witch or road saw, the contractor was able to excavate rapidly constructed, extremely narrow trenches one metre deep by 120 mm wide in preparation for the drainage system installation.
Megaflo is a geocomposite drainage system manufactured from a high density polyethylene (HDPE) panel drainage spacer core, wrapped in bidim geotextile, and provides the optimum combination of high strength and superior filtration. Bidim is a continuous filament, nonwoven, needlepunched geotextile. Advantages derived from the needlepunching process include appreciable thickness, high porosity and a high drainage capacity both transverse and normal to the plane.
Of concern to consultants, KBK Engineers, was the long-term performance of geotextiles placed in contact with the dispersive silty/sandy soil when constructing a conventional stone drain. This was addressed by the geocomposite drainage system being installed in a narrow trench surrounded by a -7.1 mm washed crusher sand with no more than 4% passing 0.075 mm. The sand acts as a pre-filter to protect the geotextile against clogging.
While the high strength structural core of the drainage system is sufficiently rigid to prevent buckling during installation, its flexibility in the horizontal plane allows for bending around any protrusions. Since it is also rigid in the vertical plane, a consistent invert gradient is maintained during installation even if laid at very flat gradients. This system can be installed with minimal bedding as the ribbed structure and minimum obstruction internal support lugs provide superior crush resistance (>200 kPa).
Maastricht explains the design of the drain, “The design was based on a soil permeability of 5 x 10-6 m/s. Varying heights of the product were installed for draining of long cuttings, up to one kilometre (500 m in each direction) and at relatively flat gradients (1%). Using long wooden wedges, it was either secured in the middle of the trench or along the excavation edge adjacent to the road layers. The trench was then backfilled with the specified washed crusher sand, directly from a modified truck, and hydraulically compacted. Varying sizes of the panels were used.”
Subsoil drains were installed along the road edge while transverse drains were installed through all the cuttings and entrances to the cuttings. To allow for maintenance and upkeep of the drainage system, rodding eyes were installed at regular intervals. As an alternative to conventional drainage, this geocomposite system provided a number of environmental benefits including the eco-friendly geotextile, minimal exploitation of natural quarried material, minimal spoil and lower emissions due to overall lower usage of diesel.
Installation of this unique drainage system also benefitted the contractor due to several factors: the elimination of 19 mm stone, reduction on drainage media quantity, use of excess material from the crushing process, construction of very narrow trenches, minimal spoil of excavated material, minimal disturbance to the existing road and the speed and ease of installation. These factors significantly increased production speed and reduced construction space thereby minimising disruption to traffic, and overall achieving a reduction in costs for the complete system.
For more information on Kaytech products and systems, visit www.kaytech.co.za