# Forum Home Renovation Retaining Walls  Where Oh Where does the ag pipe go?

## Mybel59

G'day all, 
First time poster but long time reader of this forum. I read it at work (sure beats working!) but cant log in and post as our firewalls prohibit it.........Anyway........ 
I live on a sloping block (backyard is higher than the frontyard) and recently had a inground pool installed in the backyard. To do this I had to have a site cut done in order to get the pool on to level ground. No problems there and just waiting now for summer to come along.  :Biggrin:  
The pool sits about 4 metres from my rear fence and, as I had a site cut done, I had to install a retaining wall along the rear boundary. Again no problems with that. The retaining wall is 2400 x 200 x 50 treated pine sleepers and is three sleepers high (600). It sits about 900 in from the rear fence and is about 13 metres long. 
My question is where do I install the ag pipe? Does it need to sit below the bottom sleeper with the aggregate on top or does it sit level with the bottom sleeper?  As it the retaining wall runs across the slope and not down it I am also a little unsure as to how to get the correct fall for the ag pipe. 
Any suggestions? 
Cheers

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## Black Cat

Not an expert by any means, but i would assume the purpose of the ag pipe is to remove the excess water that will accumulate behind the wall when you have heavy rain. So the logical place would be immediately behind the lowest sleeper, surrounded by aggregate to reduce the chances of soil clogging the pipe up. 
Unless the wall follows the contours precisely there will be a naturally lower end (which should become apparent when you run a level across the sleepers and check they are level. The lower end will be the one where you had less digging to do.

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## Oldsaltoz

The agg pipe should be below the blockwork to prevent mould, as above outlet should go to low end of wall to reduce digging. 
Agg pipe should have geo fabric around it and sit in 50 mm aggregate that is 3 to 400 mm deep. This will prevent the agg from blocking down the track. 
Also consider waterproofing the back of the block area down to and onto the footings joint to prevent water ingress and more mould. 
Good Luck.  :Smilie:

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## DAZ

ad pipe should always terminate at a point where flows can be discharged at a sufficient rate. For ex. a drain box. 
The water contained behind a 2.4 metre wall when saturated imposes a hydraullic pressure of 24 kPa at the base. This means flows into the drain will be  significant when the ground is saturated and therefore the pipe should terminate in a drain box.

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