The pipe should be surrounded by gravel in a trench where water moves through the ground, passes through the gaps in the gravel, and starts to fill the trench surrounding the pipe. As this happens the water will percolate into the pipe through the holes and flow out of the pipe when its installed with a fall.

A Guide to Perforated Drain Pipes | Drainfast Ltd

Perforated pipes are no longer a British Standard product. The pipes are drilled whilst wet and the semi-dry nature of the concrete used in the manufacturing process leads to spalling on the inner and outer surfaces around the holes. This is cosmetic only and does not affect the integrity of the pipes for land drainage use. Perforated pipes comply with the Department of Transport Specification for Highway Works, which states the total area of drainage holes should not be less than 1000mm2 per metre length of pipe. The CivilWeb French Drain Design spreadsheet includes analysis modules to complete both these perforated pipe drainage system calculations to ensure that the french drain is fit for purpose. The spreadsheet completes the calculations following the SUDS manual procedure as detailed below. Perforated Pipe Design - Perforations This is the area of each orifice. Areas given in mm 2 can be converted to m 2 by multiplying by 10 Although you would think that having the holes at the top would mean the water could fall into the perforations, as it flows through the ground, this doesn't offer the best performance.If you're installing a half-perforated pipe, such as half perforated twinwall, this is where the problem comes into question; whether the perforations are best facing upwards or downwards? Contrary to popular opinion, the most effective method is to have the holes facing down. Why do the perforations go downwards?