Drainage against retaining wall

[Nick J]

Hi, this is my first post on the forum, I can't find the info I need on the main site. I would like a few ideas on the best way to drain a patio that is retained by a dwarf wall. and bordered on all sides (one of which is the house)

I've got a few ideas myself, one of which would be to fall back to the house and in to a gully. Okay that seems obvious, but I'm not keen on building a fall back towards the house (neither is the client!)

I could used linear drains in line with the wall, but they didn't seem too impressed with this either.

Right I'm just going to through this out there... The dwarf wall has a standard perforated land drain behind it which we will route to a soakaway, would it be out of the realms of possibility to use this as our patio drainage (by incorporating a "reverse" weep hole in the wall) ?

What do you think? If its too much hassle I may just recommend linear drains and be done with it, what I don't want to do is build my client an unwanted paddling pool.

Cheers

Nick.

[lutonlagerlout]

linear drains look a whole lot better than a water feature
depending on the existing lie of the land you will need linear drains either against the house or the wall
its not negotiable,you can get the slit type ones where only a 15-20mm slit of plastic shows,but i am no big fan of these
cheers LLL

[Tony McC]

So, the patio would drain towards the retainer wall, and then stop just short of the masonry and have summat like a splash strip that leads to the land drain: is that right?

I'd prefer the slot drain option that LLL dislikes, but only because it would allow water to be collected relatively discreetly and directed to the land drain rather than left to find its own way through however much pea gravel and accumulated detritus. Another option would be to use a drainage composite at the back of the wall, which again would help direct water flow and eliminate much of the problem of detritus and maintenance.

If the client just doesn't like the grating on a linear channel, there's nowt to stop you laying it, say, 50mm below paving level, wrapping the grating with a geo-textile and then covering it all with 40-50mm of decorative gravel so that it *looks* like a splash strip but is actually a proper drainage channel.

[mickg]

I don't like the slot drain either, once installed there is no way to get to any of the channel below the slot to keep it clean, at least with a linear drainage channels you can get access to the full length by lifting the top off

surely on a heavy downpour wrapping the drainage channel with geotextile would stop the water from dissipating quickly and could form a puddle on the patio area unless you cut small slits with a sharp utility knife in the geotextile ?

[Tony McC]

Naah....the flow rate through a geo-textile is phenomenol, it's almost as though it isn't there!

[Dave_L]

That's a bloody great solution Tony, I like that idea.

[mickg]

after conducting a controlled test for the permeable qualities of geotextile fabric it would be true to say that initially when you pour a bucket of water onto the geotextile fabric it does in fact flow freely as photo below



but once the initial flow has reduced it actually holds water as the photo below


so we feel that the geotextile fabric needs to be cut with a utility knife to ensure the smooth flow of water as over time detrus and other debris will build up and block the flow of water

NOTE....
this is not the actual utility knife used in the experiment and is for illustration purposes only :;):

[Tony McC]

Mick, that's a woven geo-sheet. I'd much rather use non-woven materials, such as Terram 1000, BuildA, TDP115 and the like. Once wetted, they flow like the Aswan dam!

[mickg]

yeah it is woven geo textile which is a lot stronger, I stopped using the non-woven materials years ago as when it get wet it just tears like paper

[lutonlagerlout]

i thought the whole point of geotextile was that it IS NOT woven??
I use "wrekin multitrack" and believe me you cant tear that wet or dry
its a sod to cut with a sharp knife
LLL

[Tony McC]

Mick, if you can tear a non-woven geo-textile, it *must* be a landscape fabric rather than a construction geo-textile. Plantex and Mypex are easy to rip: Terram, Lo-Trak, TDP and the like will take the fingers off you before they rip!

[Mikey_C]

can't rip the tdp stuff, it is incredibly easy to slip on though!

[Nick J]

Thanks for the replies, I'm tapping into the existing SW soakaways, for the drainage. The majority are okay, but we found the most unbelievable bodge job on one down pipe. The down pipe in question connected to a length of black down pipe IN THE GROUND, which ran unconnected to a short length of black square down pipe, which ran unconnected to a length of square white down pipe! At this point and with a huge amount of excavation (It was a bank to begin with) we gave up. We tried to dig a soakaway for a new down pipe but ended up with a 2 metre hole and solid clay! Needless to say our percolation test failed miserably (I only did it as a demonstration for the client) We are due to pave this area as well with a 1150mm path so we will now re-route the guttering back a little and as all else has failed, and hopefully if Welsh water give us permission it'll have to go in the FW. A bit of a game to say the least. The other side of the house is a completely different matter with a lovely old salt glaze pipe going to a soakaway that seems to work fine during our tests. This is what we intend to tap in to, to drain the section of paving that this post originally concerned. We have now just about completed our excavation and I have discussed options with the client, they now seem okay to the idea of a simple gully pot in the corner of the wall, from my calculations that should be enough as its not a huge surface.

I'll post some pictures of the finished job, Indian Sand stone I'm afraid, but what we've laid at the front of the house has gone down rock soild... Its all about the frost proofer and covering IMO.

Cheers nick.

[GB_Groundworks]

on the geotextile question never use that woven crap, haha its what they sell in b&q we use terram 1000 etc on 4.5 x 100 metre rolls its hard enough to cut with a sharp stanley and i have hung a 1.5 ton mini up on them before with the narrow utility bucket on.

i'm going to find some now and test it haha back in 10

just uploading video i can confirm that wet terram 1000 can hold an 18 stone ground worker

http://www.youtube.com/watch?v=-digNQHeb48

held a bit of residue at the end but there was a lot of junk in the watering can.

could dave or tony explain this video

http://www.youtube.com/watch?v=aHVQNMxVhEI

is it subbase or top layer?



Edited By GB_Groundworks on 1266075079

[flowjoe]

LMFAO

I am sure the back wheels lifted slightly there Giles.

Thought you were peeing in the bucket at first

Good work :laugh: