Retaining Wall Advice - DPM & Drainage

[Furton]

I'm the process of building a retaining wall for my patio and I've just finished the concrete foundations and ready to move onto the breeze block walls. The intention is build the wall out of concrete breeze blocks and then render the visible blocks and paint it white. The wall will be circa 1m high and will have a small parapet.

I've been reading a lot on Paving Expert and came across the following guide for building a retaining wall.

http://www.pavingexpert.com/featur03.htm

I'll be installing a DPM as per the guide however do I really need drainage channels?



In terms of backfilling, you can see there's load of excavated soil/clay under the blue sheet and plenty of old slabs etc in garden, can I use this to build it up to the level I need, then lay the sub-base? I was hoping I can get away with compacting the soil as backfill as I go?

 

[a1ex2001]

I would say drainage hole are more important than a decent for a retaining wall you don't want the water build up behind it.

 

[Windle]

You want a nice free draining material behind a retaining wall, something like 6N.

Drainage channel/weeper holes are essential as above. Plenty of wall failures relate to drainage issues.

 

[Furton]

You want a nice free draining material behind a retaining wall, something like 6N.

Drainage channel/weeper holes are essential as above. Plenty of wall failures relate to drainage issues.

I've got a grab bag of ballast 20mm to sharp sand, assume I can use that as backfill?

 

[john_s]

I've got a grab bag of ballast 20mm to sharp sand, assume I can use that as backfill?

You'd be better with a single size stone - i.e. no fines - behind the wall for free drainage.

 

[Furton]

Right, thanks for the advice so far. Had a very productive week off work helping the bricky with the retaining wall and breaking out the old "patio".

However, I've got some questions which I need some advice on. On the below picture, the patio will eventually fall away from the house (on the right) towards the retaining wall. The DPM is set 200mm above the ground level and there are weep holes (with copper pipes) set at 800mm intervals just below the DPM. I've backfilled the first 300mm behind the retaining wall with 6N aggregate. In terms of drainage, can I just run a 100mm strip of decorative aggregate between the retaining wall and patio and allow the water to drain, or do I need to put an Eco drain in?



Behind where the above photo was taken I've uncovered a drain top which was circa 200mm below the previous flower bed. The cover cracked when I tried to lift it open. I've poured some water down and it seemed to flow away clearly, hence ideally I would retain access to it. It's an 8inch diameter opening. What do I need to extend this to the new finished floor level? Can't seem to find anything suitable at the moment.



Finally, I'm installing an Eco drain between the patio that runs down the side of the house and where the new patio starts at the back. I need to connect it into the rainwater drain as in the below photo. How do I drill into a clay pot to make the connection? Or do I need to remove it and extend with new plastic?

 

[Furton]

Anyone?

 

[Windle]

Just run the new drain channel to under the down pipe and tie into existing outlet.

Can you not just run new pipe section of marginally smaller diameter into existing drain and up to new GL?

Eco drain for between patio and retaining wall not essential but personal choice as to what you want.