A unique addition to the FRC™ Pipes range is the slotted pipe, an ideal solution for combined subsoil and stormwater drainage systems.
Range
Slotted pipes are manufactured in standard 4m lengths in Class 4 for 225mm to 750mm diameters. Typical slotting configuration involves the use of two rows of 300mm x 5mm slots.
Strength
All classes of FRC™ pipes may be slotted however this reduces the crushing strength of the pipe by approximately 10%.
Flow in Pipe
To determine the flow rate of pipelines use the Colebrook-White formula where k = 0.060. Refer to the 'Fibre Reinforced Concrete Pipes Product & Design Data' booklet for further information.
Approximate proportion of full pipe flow below slots:
Slots down 25%. Slots up 80%.
Trenches
Trenches should be as narrow as practicable, allowing 100mm working space each side of the pipe. Trench depths should be such that, allowing for adequate fall in the line, pipes can be laid at an average depth which will drain the maximum area around the pipeline or each section of the line where sumps are incorporated. The possibility of traffic loading on sections of the line must not be overlooked and should pipes be near the surface at such points, a change in pipe class may be necessary.
Bedding - Filter Material
For maximum drainage into each pipe, and to prevent blockage of the slots, suitable filter material should be used as bedding. See picture A.
10mm through to 19mm one-size aggregates are suitable for most firm ground situations.
In soft and permanently waterlogged ground, an ideal filter material would adhere to the following specifications:
One third - 10mm screening
One third - 6mm screening
One third - 3mm screening
Selected porous material (coarse sand or gravel if available) should then be placed and tamped in 75mm layers, leaving room at the top of the trench for a final layer of good top soil of sufficient depth for plant growth, if required. For a more detailed assessment of available materials consult your Geotechnical Engineer.
Effective Drainage
The drainage effect of a single sub-soil drainage pipeline depends on the type of soil to be drained and the depth at which the line is laid, as shown in the following table:
Three typical arrangements of sub-soil drainage lines are shown in the picture B 'middle right'. In each case collector lines, spaced according to soil arrangements, feed into a main drainage line.
Slot Details
Effective Drainage of Road Pavements
It is now realised, with flexible pavements especially, that bitumen sealing coats and asphaltic concrete wearing surfaces are far more permeable than originally thought. If boxed pavement construction is used, adequate provisions must be made to eliminate the rainwater which has infiltrated from the surface together with leakage at cold joints in the seal and at the pavement shoulder interface.
In conjunction with the New South Wales Department of Main Roads, James Hardie have carried out early trials using 100mm diameter FRC™ pavement drainage pipes. Tests showed these pipes have both ample strength to withstand substantial construction loads at only 75mm nominal cover together and ample capacity to drain pavements even when subjected to high rainfalls during construction and before sealing.
Similar design criteria for pipes in trenched drainage systems can be adopted. The lengths of each drainage system i.e. the distance between shoulder outlets or turnouts, should be as follows:
Where a 0.5% grade is difficult to achieve turnouts must be provided at more frequent intervals.
Typical detail of trenchless drainage of a boxed pavement. (used when base is rock or other stiff material) are shown in picture C.
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