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Retaining wall weep holes needed?

Posted by nancyd0808 Michigan USA (My Page) on
Mon, Jun 4, 07 at 6:40

I am planning to replace an existing wood retaining wall that is rotting and falling over with a Unilok block wall. It will be 3 feet tall at the highest point and 122 feet long. The area is very shady with mature maples nearby.
The soil is sandy, but damp due to the shade.

The contractors I trust all mentioned putting in a French drain behind the wall. One seemed to think that I need to add 4" pipe weep holes on the front of the wall, that he would cover with small grates.Esthetically this doesn't thrill me, and nothing I have read indicates I have to do this. Is it a good idea, or can I just run the drain off the ends of the long wall?


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RE: Retaining wall weep holes needed?

  • Posted by laag z6CapeCod (My Page) on
    Mon, Jun 4, 07 at 7:19

Segmental retaining walls, like unilock or any of the many, weep between the blocks since there is no mortar. You should have perforated pipe running at the bottom of the cut or fill to carry away water so that it never builds up in the first place.

The wall should have well draining gravel behind it from top to bottom. Then there is no water build up, it just goes down to the perf pipe. The perf pipe needs to be able to carry the water to daylight, a drywell, or a leaching trench away from the wall.

There is no reason to have a 4" opening above grade on a unilock wall that I know of. This is something that would be done with a poured wall or timber wall. My guess is that the guy who said you needed the weep holes is older or at least old school and not up to speed on segmental wall construction techniques that have been well developed over the last 15 years or more.


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RE: Retaining wall weep holes needed?

Thanks for the quick reply! That was my impression, and I think I have him convinced that all he has to do is run the sock pipe (which he was doing anyway) to the ends of the wall and have plenty of gravel around it. I will probably just drain it at the ends, since the height slopes downward on each end of the wall.

It just sounded really ugly to have those drain holes in the front and I would worry about cracks from drilling that might weaken the blocks. I have had other walls built at my prior home and know that the wall will be wet following rain, but I just wanted to be sure I wasn't missing something here.


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