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View Full Version : Drainage behind a block wall?


nlminc
07-11-2006, 11:53 PM
A couple of months ago I refused to do a block wall/patio job for a neighbor. The job was just to much for me and I've only done one block wall about 9 years ago.

My neighbor received 3 quotes 15k, 23k and 30k. They went with the 15k guy.....he was looking forward to working with this stone/block because he never worked with it before! :dizzy: My neighbor told me he said this! I warned her on the low quote and the comment about his experience with the block but they went with the guy.

To my question.....

I noticed they backfilled the wall that stands 5-8' high with stone dust (thought this required crushed stone?) and there are no visible drains coming out of the wall. There should be drains correct? I couldn't believe there were none. I didn't want to come across as ripping the company and the neighbors seemed happy with the job, so I kept my thoughts to myself.

It has taken the company 2 weeks and they are still not finished.

nlminc
07-12-2006, 05:27 PM
No takers?

D Felix
07-12-2006, 05:37 PM
There's a lot more activity here in the winter than in the middle of the season....

There should be clean, angular stone behind a wall of that hieght, for at least a foot of depth behind the wall. There should also be drainpipe at the bottom of the drainage stone, I believe NCMA states it should daylight every 40 feet in length.

Just because it was the first time working with a particular type of block doesn't mean much. All SRW's go in in essentially the same manner, it's just the minor details of each manufacturer's block that differ. That being said, it doesn't sound like this guy knows what he's doing...

Is there any geogrid reinforcement in the wall? For 15K, I'd have to assume not....

cedarcroft
07-12-2006, 05:38 PM
sounds wrong to me. stone dust will compact and not allow for proper drainage. no drain pipe in the wall will allow hydrolic pressure to build up behind the wall and blow it out eventually. I am no expert but drainage, geogrid and a solid,level base are the 3 most important things in an SRW.

D Felix
07-12-2006, 05:46 PM
That being said, I've still seen a Keystone Compac wall stand (5-6' tall, vertical) for 5+ years with dusty limestone backfill without any major problems before we tore it down....

I started a thread on that project almost 2 years ago now....:)

Mike33
07-12-2006, 08:24 PM
sounds wrong to me. stone dust will compact and not allow for proper drainage. no drain pipe in the wall will allow hydrolic pressure to build up behind the wall and blow it out eventually. I am no expert but drainage, geogrid and a solid,level base are the 3 most important things in an SRW.
We must of went to the same school*newusflag* I can not agree with you anymore.
Mike

D Felix
07-12-2006, 09:57 PM
After reading my last post I guess I should have said that even though that wall stood that long, it was most definately built wrong and it was eventually doomed to fail. :) The only thing that saved that wall was the soil conditions; the soil was as stable or more stable than any I've ever seen/worked with.....

It still should have been built *right* though!

paponte
07-12-2006, 10:10 PM
I would have to agree that there should be at least 1' of clean drainage stone behind the wall, with fabric seperating it from the fill. There should also be drainange to light as mentioned every 40'. Depending on the stone and the conditions, most walls over 4' would require the use of geogrid. The first course should also be sunk a minimum of 1" per foot of wall height, again depending on wallstone.

Mike33
07-12-2006, 10:36 PM
After reading my last post I guess I should have said that even though that wall stood that long, it was most definately built wrong and it was eventually doomed to fail. :) The only thing that saved that wall was the soil conditions; the soil was as stable or more stable than any I've ever seen/worked with.....

It still should have been built *right* though!
An interesting point i seen on Modern Marvels 1 night was most of the time even when something is not built right they dont like to fall down. I still like the way of building things right. Most of the time my walls are over killed on stone for back fill but when i go to bed tonight and it is dumping down the rain i dont have to worry about my walls failing.
Mike

nlminc
07-12-2006, 11:07 PM
Thanks for the feed back! Yeah, I was standing there looking real hard for that drain pipe.......... :eek: nothing and then I remembered seeing the job in progress a week or so ago and noticed they backfilled the wall with stone dust. They ordered so much stone dust they had enough left over to make a decent 2 car parking space in the front of this yard.

When I heard he was doing the work for 15k I was skeptical. I thought he would lose his shirt or walk away. He still has not completed the cumberland stone steps. They said they didn't order enough and would be back. That was a week ago!

Please forgive me, but what is geogrid?

Dirty Water
07-12-2006, 11:23 PM
Please forgive me, but what is geogrid?

Geogrid ties the wall into the soil behind it. Its a high strength polymer webbing that you lay between your blocks every few courses and then run back into the hillside. Geogrid is what anchors your wall to the hillside, so you don't have to depend on the mass of wall to hold the hill up.

http://www.nitterhouse.com/masonry/products/retaining_walls/geo_grid2.jpg

http://www.matsuo-gr.co.jp/web/blick/abr/images/geogrid.jpg