"French" drain 'tile'

[Externet]

Hello all.

Having a problem with 'tile' meaning a perforated pipe.  But hey, it is English and am not the one to fix it 🥴

 

[ Image borrowed from the net.]

Unsure of positioning the perforations under the pipe half for proper drainage.  Seems like the gravel below the perforations level will always be flooded, (never flowing upwards to drain into the pipe) Shouldn't the pipe have no gravel under it, and perforations on sides ?

What is the rationale ?

[Kartazion]

27 minutes ago, Externet said:

Unsure of positioning the perforations under the pipe half for proper drainage.  Seems like the gravel below the perforations level will always be flooded, (never flowing upwards to drain into the pipe) Shouldn't the pipe have no gravel under it, and perforations on sides ?

What is the rationale ?

Hello.

The slits should be at the top and the bottom of the pipe serves as a bowl. On another side the drain must be sloping. About 1 cm per meter. The accumulation of the water downstream means that by its level will cause water to pass through the slits. The gravel below the pipe is probably because if it touch the ground, it will plug and accumulate this mud in the drain. 

Be careful during your installation because it is said that for specific condition in agricultural spreading, the slits of the drain must be downwards!

[zapatos]

If the goal is to route water into the pipe and have it flow through the pipe to an outlet, then the perforations would be on top.

If you are installing a French Drain, then the perforations are on the bottom. Holes on the bottom and gravel all around both work to ensure soil does not work its way into the pipe which will eventually cause the drain to fail.

Water rising above the level of the gravel beneath the pipe will enter the pipe and flow away. If the water doesn't rise above the level of the gravel then it will drain into the soil. Water draining into the soil is just like the water that flows away through the pipe; that is, both are moving away and thus no longer constitute a water problem.

[iNow]

Gravel also slows the water. Slows erosion. Some water seeps downward into soil. The rest (that which is above the layer being absorbed into soil) flows away through the pipe. Downward perforation placement is correct, as is ability for underlying gravel to saturate

Edited July 2, 2021 by iNow

[Kartazion]

I think the most rational explanation is given by @zapatos.

[studiot]

5 hours ago, Externet said:

Having a problem with 'tile' meaning a perforated pipe.  But hey, it is English and am not the one to fix it 🥴

It is refreshing to have a non controversial subject to discuss so +1 for introducing it.

5 hours ago, Kartazion said:

On another side the drain must be sloping.

This is a worthwhile addition to the discussion, though it is not always necessary to have a slope or fall in the pipes, they are often laid this way and indeed in sloping ground it may not be avoidable. +1, making your reputation now neutral.

🙂

Externet has introduced two cases when non sealed pipework is used, both being for 'drainage' purposes and you have added a third in irrigation.

Just to get irrigation out of the way quickly it is normally laid on the surface for the water to follow nature and trickle down into the soil.
Clearly this would never be done in cases where the soil already contains sufficient water. Sufficient water does not mean saturation by the way.

But Externet asked about 'French Drains' and in particular 'tiles'.

The main purpose of the drainage is to lower the water table in both agricultural and ground engineering (foundations, basements etc) applications.
The term French Drain refers to the entire system, not just the pipes.

The water table is the boundary between saturated and non saturated soil (or rock) and has a posh name 'the phreatic surface'.
Below the water table the ground is saturated and above it will generally still contain water but at lower concentration and so be unsaturated.

If the water table is too high for part or all of the season then (some) crops will not grow satisfactorily.

The original drain indeed used V shaped clayware tiles, laid upside down or apex at the top.
These can be traced back to Roman times.
These were not perforated but simply laid, butted in a line, at the bottom of a trench.
The inverted V acted like a little roof, protecting an open space beneath, from being filled with soil
Because the joints were 'open', water percolated into the open space and spread along the line.
A network of such trenches would reduce the whole water table in a field and perhaps lead to a deeper side ditch to drain away excess water.
It is often not necessary to lay these to falls, this depends upon local circumstances
Such tiles are still available but have generally been replaced by short perforated round clayware pipes, which are still called 'tiles'.
More recently long lengths of perforated and unperforated plastic pipes have been introduced.
Often the tiles or pipes are sourrounded by some granular material such as a type of gravel called 'pea gravel' to slow the ingress of fine soil material which would eventually clog the pipe. But the soil for supporting the crops is then backfilled over the top, as they won't grow in gravel.

OK so that is the agricultural use now for the engineering use.

Saturated soil exerts a much higher pressure on retaining walls, foundations, basement walls and the like, than unsaturated soil.
This is known as 'active pressure' in soil mechanics.
This is clearly undesirable and has been the cause of many a structural failure.

To avoid this pressure structures subject to earth pressure are protected by attempting to totally lower the water level to at or below the lowest structural level.
In order to achieve this the backfill behind say a retaining wall or under a foundation is made from 'suitable material'.
This suitable material is usually granular right the way down from the surface to the bottom, where a porous or perforated pipe collects and distributes water in the same way as the one in an agricultural field, but this results in a more drastic reduction in the water table level.
This technique is also used to stabilise earth slopes (eg in the sides of cuttings) that might (would) become unstable with a higher water table.

 

Hope this helps.
 

[Externet]

Thanks, gentlemen.  +1

Opinions varied, but OK.  The task in mind is not agricultural nor leach field; but ocasional plain basement light moisture ingress and am ready to dig and set a perforated pipe in a part of the inside perimeter.  My basement already has such 'French drain treatment' on 75% of the perimeter as house was bought.  I should add like 10 metres to have all of it 'treated'

Will re-read the suggestions and explanations to properly position the pipe perforations (not tiles)  Pipe will wear a sock too to minimize erosion.