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If there is no available outfall, is a soakaway a good alternative?

It may be possible, provided it is deep enough to reach a suitably permeable subsoil layer. This can be checked by excavating a hole to the appropriate depth and observing the water level during a wet season. (Testing this when it is dry is not valid)

What sizes of Primary Mains Drainage Pipes are required?

We use the manufacturers flow rate charts to help establish the sizes required. The size of the area, gradients and the precipitation rate to be dealt with by the scheme design will all be taken into consideration to establish the correct size of pipes required.

What sizes of Lateral Drainage Pipes are required?

Generally these drainage pipes, also known as laterals, are short runs at fairly close centres; therefore each pipe is required to drain only a limited quantity of water. Sizing is dependent on the same factors as the primary pipes.

At what spacing's should the laterals be installed?

Obviously closer spacing’s are more effective than wider ones, so sometimes this comes down to cost. The function of the laterals is threefold and these factors will all be used in calculating your specific requirements.

  1. They drain the gravel layer.
  2. In a root-zone mixture or in soil, they receive water which filtrates through that material.
  3. In a slit matrix they accept discharge from the slits as well as discharge from the soil or root-zone mixture.

At what depth should laterals be installed?

They must have a gradient which gives a constant fall to where they discharge into the mains and therefore this determines their depths. As a general rule a minimum depth of 450mm is required.

What backfill should be used in the pipe trenches?

The most durable backfill is a 10mm or smaller sized clean stone. The problem with larger sized material is that the pore spaces between the gravel are large which, although initially providing rapid flow, soon allows fine soil particles to migrate into these spaces thus causing water movement to be seriously reduced or to cease completely. Also with larger size stone it is difficult to get grass growth over the drains.

How close to the surface should gravel backfill be placed?

Generally it would not be closer than 150mm, although this is not an easy question to answer and we would prefer to visit your site to enable us to give a more accurate answer. So please contact us.

Can gravel or granular material be brought right up to the surface?

Never! This is bad practice and when the material is at the surface, the detrimental infilling with fines takes place very quickly. Also, whereas the addition of sand progressively improves the texture of the surface soil, introducing gravel or granules is seriously detrimental to it.

How much does it cost to construct a football pitch?

It is very difficult to suggest a figure in view of the many issues that come into the calculation including existing ground conditions, levels, outfall for drainage, existing grass cover, geographic location and site access. For these reasons we provide a free site visit and a subsequent detailed specification and quotation that is tailored to your specific needs.

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From the initial call to Grassform Plant Hire we have received a service that has been superb, they have advised on all aspects of the construction process with minimal impact on our day-to-day lives and employed the best techniques to end up with a fantastic fishing lake that we shall have many…

Mr B
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