Installing Underground Drainage Pipes

Digging the Drainage Trench
The width of the trench should be the size of the pipe (usually 110mm in domestic situations) plus 300mm. Hence for a standard 110mm pipe the trench width should be 410mm. Many small diggers come with a bucket that is this size for exactly that reason.

When digging the trench, the material that you dig out can be saved for back filling provided that all sharp stones and flints are removed. It is best to sieve the soil to ensure that it is fine and free from stones. We do not recommend back filling trenches with clay or heavy soils. If the bottom of the trench is free from stones and is of fine soil, it can be used as the pipe bed, but it is more usual to use a granular material such as pea shingle for this purpose. You should ensure when purchasing this material that the shingles are ideally no larger than 10mm.

Preparing the Pipe
Pipes should be cut to size using a fine toothed saw. All underground drainage pipes come with either a socket end or a plain end that has been chamfered.

Drainage sales recommends that whenever you cut a pipe to size you must always make sure that the cut end is chamfered. This can be achieved using a rasp or a file. If you leave a square, rough cut end on a drainage pipe you run a real risk of damaging or misplacing the seal when the pipe is inserted into a fitting or an inspection chamber. For the same reason, a proprietary silicon lubricant should be used on all joints to ensure a smooth insertion into the fitting.

Laying the Pipe
Pipes should be laid on fine soil or a bed of granular 通渠服務  material as described in the section above. Pipes should be laid to a fall of 1 in 40 for standard domestic installations. This means that for every 40m the pipe travels horizontally, it should drop by 1m vertically. The method of measurement, metric or imperial, is actually irrelevant as long as 1 in 40 rule is obeyed – a 1 foot drop in a 40 foot horizontal run is exactly the same. Pipes fall at this level in order to create a self cleansing effect, meaning that the flow of liquid at this level of fall is sufficient to carry away any solid matter. If the pipe run is too shallow, the flow will be insufficient for the solids to be carried away. Conversely, if the pipe fall is too great, the liquids will flow too quickly, leaving solids behind. This will quickly result in a blocked pipe.

Filling the Trench
Drainage Sales recommends that the sieved material that was dug out earlier can be used to side fill and back fill the trench around the pipe. If you have left over granular material from the pipe bedding then this can also be utilised.

You must fill at least 300mm over the top of the pipe before any mechanical compaction of the soil can take place. If there is any danger of future damage to the pipe by items such as gardening forks etc you should protect it by putting a paving slab or similar protective item above the pipe and below the finished ground level.


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