How much bank can a "mafia block" hold back?

[Scooby074]

Im just thinking about a potential project this summer.

I might dig into the bank here to make a area to store firewood. Maybe 8'x14'? At the deepest part of the bank it will probably be 8' vertical, maybe 10 '? Not sure yet. Clay soil and lots of water run off, which could be a huge issue re: drainage.

Anybody build a retaining wall with these blocks before? Ive seen them used to build bunkers for mulch and soil and the odd retaining wall, but im not sure what if any special things I need to do. These blocks could be a cheap way to build a wall. What about a base? Ive built Allen Block walls before, but this would cost far too much for me if I was to use them.

Other costs would be a crane at $100/ hr.

Just throwing it out there.. anything Im missing? Might be more work than its worth...

Here's a rough layout.

 

[vtsnowedin]

Dose the ground slope up beyond the top of the proposed wall? If so the weight of that earth has to be considered and in a wet fluid state as in the spring. Other then that you should toe in the first course of blocks so they are half a block below your finished front grade and back fill at least a foot wide behind the blocks with free draining material to reduce soil pressure on the wall. I'd tip it back one on twelve so that any frost action has to get it plumb before it can start to tip it. That way when it thaws out gravity pulls it back into place not pull it further over.

 

[Baby Grand]

For stability of the high, long wall can you make it an arc rather than a straight shape? Just a few feet of rise would give you a much stronger structure.

 

[dave1949]

With the correct step back from one course to the next, and good drainage stone and drain tile behind the wall, you should have no problem with the height. That's my guess.

 

[BuilderML]

A good 12" base of stone under the wall with stone behind the wall installing fabric between the stone and earth. Also a perf pipe at the first bottom of the first block draining to daylight. You should be fine stacking your wall level with interlocking your corners,if you are worried set each block back alittle but i don't think you will need to with stone behind the wall and your corners interlocked. Have fun.

 

[vtsnowedin]

If you don't want the stepped look just tip the first course back 1-12 then stack them smooth. The inside courner will be a fudge job but some fabric or crushed stone behind it will be fine.

 

[Scooby074]

Dose the ground slope up beyond the top of the proposed wall? If so the weight of that earth has to be considered and in a wet fluid state as in the spring. Other then that you should toe in the first course of blocks so they are half a block below your finished front grade and back fill at least a foot wide behind the blocks with free draining material to reduce soil pressure on the wall. I'd tip it back one on twelve so that any frost action has to get it plumb before it can start to tip it. That way when it thaws out gravity pulls it back into place not pull it further over.

This is a concern of mine.. There is a pasture above this wall, a few acres, sloping uphill. So that means a lot of water and ground pressure. The more I think about this, the more I think its a bad idea. Interlocked corners and proper drainage for sure, but i think even pitched back at the top there will be too much pressure.

 

[Scooby074]

A good 12" base of stone under the wall with stone behind the wall installing fabric between the stone and earth. Also a perf pipe at the first bottom of the first block draining to daylight. You should be fine stacking your wall level with interlocking your corners,if you are worried set each block back alittle but i don't think you will need to with stone behind the wall and your corners interlocked. Have fun.

That was what I was thinking for drainage and base. Similar to what Ive done in the past for Allen Block. This bank is a bit of an extreme case. In spring it turns into spongy HEAVY clay. Lots of water coming down all year too.

 

[Scooby074]

With the correct step back from one course to the next, and good drainage stone and drain tile behind the wall, you should have no problem with the height. That's my guess.

One issue I just thought about re: step back is crane time. Id need the crane onsite for a lot longer due to having to backfill as I step backed as apposed to just building a sheer vertical wall and backfilling later (although that isn't the best procedure). Hours and hours of crane time aren't really in the budget.

 

[vtsnowedin]

It just means you have to do the work properly. If you use 3x3x6ft. blocks stacked four high with 1.5 feet below grade the weight of the blocks will almost equal the weight of the soil removed so you have it balance between before and after condition. Divert any surface water comeing down to the wall around it so it cant saturate the soil behind the wall and build the wall with good drainage as has been said. If you batter it back you will have a three inch wedge open at each course at the corner joints. To make it not look half baked fill these with sack crete or concrete cast in place.