# Retaining wall



## Limapapa (Nov 2, 2008)

I have a log retaining wall 50ft long X 2 1/2ft high. After some heavy rain storms the wall has developed a severe bow in the middle.Because of the type of nails used,it's very difficult to pry the logs apart;I'm wondering if it would be ok to cut the log wall in sections with a chainsaw, then tilt the sections back slightly beyond vertical,and erect an Allan Block wall in front of the logs. Also, since this is a fairly low wall, would the smaller blocks provide adequate support?

Thank you for any advice


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## Marvin Gardens (Sep 30, 2008)

I would not cut the section out unless you want a large pile of soil deposited down the road and possible you underneath it.

First off there there is anything of value that is beyond the retaining wall then get some help quick. If this gives way it could move a fair distance before it stops. I have seen this types of situation in the past and they are not pretty.

If that is the case then get your insurance company involved. They would rather pay for easy repairs rather than massive repairs.

On the other hand if there is no danger then you have to take the pressure off the logs. This would be done by getting the soil off the backside which will get rid of the pressure.

Once this is done you can take a breather and decide what to do.

But cutting that out is the last thing I would be doing. It is like having the emergency off switch inside the meat grinder. There is a lot of pressure and you have no idea what would happen.

I was a timber faller for many years and have had 200 foot logs bent between trees and the pressure is unpredictable. I had a lot of friends killed because they guessed the situation wrong.

There are old fallers and bold fallers but there are no old bold fallers.


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## Marvin Gardens (Sep 30, 2008)

Limapapa said:


> Thanks for your response Marvin,but as I indicated the wall is only 2 and a half feet high,and the actual soil height is no more than 2 ft. I was just wondering if there was any reason why I shouldn't leave the logs in place and just install the blocks in front of the log wall.


Don't underestimate the weight of dirt. My guess is that there is at least 8 tons of dirt sitting on ball bearings (lots of water) behind that wall waiting to go somewhere else.

One cubic yard of average dirt weighs about 3500 pounds. With high water content that figure can rise to 4500 pounds.

It takes a lot of pressure to do what you are describing. The water will make the dirt very fluid. The is what makes a lahar so dangerous. Granted you don't have a lahar but lots of water in the soil on a hillside or behind a barrier is dangerous.

Cut out the logs at your own risk.

If you want to shore it up you will have to dig down on the front and put something in the ground far enough to hold back the wall. Just resting something on the ground in front of it will not be enough unless it outweighs the mass behind the retaining wall. You need some mechanical advantage.


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## amdspitfire (Feb 5, 2008)

Don't you want to increase your usable space in front of the retaining wall? Imagine the thickness of the block plus the backfill that is required, it could bring your new wall 2 ft closer. When I did mine, I removed all of the old lumbar retaining wall and even cut back the dirt a good amount to create a larger area of space on the flat ground.


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## chad4290 (Nov 28, 2008)

i would consider redoing it if possible. maybe with new block or log. with geogrid so it has something to hold the wall besides just vertical support. don't forget fabric and 3/4 stone for drainage. or similar.


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## yesitsconcrete (May 11, 2008)

uh oh, there's the answer,,, least that'd certainly hold ME back :laughing: see any 8 day clocks around ? ? ?


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## yesitsconcrete (May 11, 2008)

oops, dble post


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## yesitsconcrete (May 11, 2008)

apologies to those who think otherwise :laughing:


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## Stillwerkin (Nov 24, 2008)

Whatever happens with the existing wall, the long-term solution will have to include some sort of water diversion/drainage system. 
No water=no hydrostatic pressure.
I can't remember what these are called, but they're basically a perforated plastic pipe with a filter sock over it that carries the water away from behind the wall and drains it elsewhere. 

Saw a "This Old House" show with the same situation and they also used tarping and a lot of stone backfill.


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## 4just1don (Jun 13, 2008)

its called drain tile


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## beranbr (Jan 9, 2009)

I would recommend taking the wall down because obviously you have quite a bit of hydrostatic pressure built up behind the wall. I would rent a mini excavator and tear the wall down and while you have the machine dig out for the new wall. If you have about 2-3 feet in front of the the existing wall you shouldn't have to move a whole lot of the dirt and it would make it much easier to install the new allan block wall. If the have the room in front of the wall here is what you need to do.

1. Tear the existing wall down.
2. Dig you base trench 2-3 feet in front of where the old wall sat. The trench needs to be 12 inches deep and 2 feet wide.
3. If there is heavy clay I would recommend putting geo-textile fabric down in the trench and running it about 4 or 5 feet up the hill behind the wall before your base rock goes down. The base rock should be something like a 3/4 modified stone (crush and run) and needs to be at least 6 inches thick. Put it down in 3" in lifts if you are using a vibratory plate compactor, but if you are using a jumping jack tamped you can do it in 6 inches.
4. Once you have your base rock down and tamped, lay your base course in the trench about 6 inches away from the front of the trench. Make sure every block is level side to side and front to back and level to each block that is next to it.
5. After the base course is laid place a 4" perforate drain pipe behind the block in the base trench, make sure you use a sleeve or fabric to cover the pipe so it doesn't become clogged up. The pipe should be vents to day light to allow the water to drain freely away from the wall. Then fill the core of the blocks and at least 2 feet behind the wall with a clean drain stone such as #57 stone. Bring the level of the stone up to the top of the base course block and then tamp or consolidate it. Also, fill in front of the blocks to make sure they do not move forward at all, do this before tamping. DO NOT use a jumping jack tamper or heavy machinery to tamp the stone behind the wall or use heavy machinery behind the wall while it's being built. Use a vibratory plate compactor.
6. Next, lay down your first layer of geo-grid. It should be 2 feet wide and run the total length of the wall.
7. Lay your next layer of block, back filling 2 feet and filling the cores of the block with your #57 stone and then compact the stone with a plate compactor.
8. Repeat step 7 and then run another layer of geo-grid.
9. Two more layers and you should be up to 2 feet in height. Now place a layer of geo-textile fabric down on top of the last course and backfilled stone or if you installed geo-textile fabric because there is heavy clay, wrap the fabric back up over the back filled drainage stone and onto the top of the previously installed wall blocks.
10. Place the last row of blocks and fill the cores with #57 stone.
11. Place the capstones on the wall, make sure you glue them down. Then, backfill the rest with good topsoil mixed with a some sand and some organic matter. This is ensure that the soil drains well and does not retain water.

Now you will have a wall that should stand up for a long time.


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## jpmildge (Feb 6, 2009)

I agree with beranbr. Your wall has been compromised. Getting it back into position would be an absolute bear of a project. If you do decide to take the time and $ to build a new wall the correct way, definatly remove the old wall. Leaving it will definatly compromise the new wall down the road.


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## beranbr (Jan 9, 2009)

I would definitely take the wall down, like I said in my earlier post. There is obviously hydrostatic pressure building up behind the wall. If you simply build a wall in front of the existing wall you are going to have the same problem, except it is going to be a more expensive one because you would have to take down two walls.


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