To geotextile or not to …

[Alan Ambrose]

For french drains / perforated drainage pipes in clay - would you geotextile (and have this possibly silt up) or not (and have the drain possibly silt up)?

 

A quandry / puzzle / dilemma?

[BadgerBodger]

Tough call. Are you draining groundwater or managing surface water? 
 

As a general rule I’d say textile all the way. In some exceptional circumstances I’ve seen them block (using non-woven).  But these were truly exceptional.

[Alan Ambrose]

Ah, groundwater.

[G and J]

56 minutes ago, BadgerBodger said:

Are you draining groundwater or managing surface water? 

OK dumb question alert: what’s the difference and which does rainwater count as?

[BadgerBodger]

Groundwater comes up/across, surface water comes down.
 

Rainwater would generally be surface water until it meets the water table.
 

Most French drains are dealing with surface water only.
 

Land drains can be dealing with either or both. Land drains tend to be used to manage the water table (in drained land) or alleviate pressure (behind retaining walls). There are variations on the theme . 
 

 

 

 

 

 
 

[Alan Ambrose]

So groundwater potentially has more silt in it.

[Alan Ambrose]

Other opinions on the geotextile or not question?

[crooksey]

No membrane, mix of pea gravel with some coarser stones for bedding/around pipe.

 

Make sure every inspection chamber has a catch pit of at-least 100mm., regularly clean out the silt.

 

It would also be advisable to have the runs jetted every 5 years.

[jfb]

No membrane in clay. Membrane if sandy.

[Conor]

Make sure you use 100mm perforated pipe instead of 80mm. Also, decent bed of clean gravel UNDER the pipe. You want the gravel to do most of the work and pipe only come in to play in heavy flow situations.

[Alan Ambrose]

Thanks guys