Drilling Concrete

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Russ Hanscom
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Re: Drilling Concrete

Post by Russ Hanscom »

On the deadman topic - strongly consider leaning the wall into the loads so the pile of dirt will tend to push it upright. Otherwise you will have a leaning wall. I am not in favor of walls build on soft foundations - a hard foundation gives you a much better chance at controlling future movements and it will move.

Put a piece of PVC pipe or similar over your guy rods to slow down corrosion.
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BadDog
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Re: Drilling Concrete

Post by BadDog »

And bed them in gravel for drainage.
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John Evans
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Re: Drilling Concrete

Post by John Evans »

Common sense thought here ,add drains in the back fill area.
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seal killer
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Re: Drilling Concrete

Post by seal killer »

All--

Hmmm. I am thinking I better redesign this wall. But, here are some particulars . . .

The wall sits on very solid ground. When we excavated, the Cat 953C ran into ledge rock at the floor of the hole. We had to saw through it to place the septic lift pump. Everywhere I've looked, that ledge rock extends outwards towards the edge of the ridge. BUT, I do not know for certain that it is under the wall. And, I have to know for certain or redesign.

The wall needs to reach up to grade level. That's at the 10 foot level, which means a wall consisting of five, two foot high blocks high. Even though the blocks "lock" together, that is no guarantee they will not lean.

The backfill will be 3" to 4" river rock. It drains exceeding well and will conduct the water over the cliff.

I will redesign the wall. Arrgggh!

I'll post my redesign(s) here.

Thank you!

--Bill
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seal killer
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Re: Drilling Concrete

Post by seal killer »

Russ and BadDog and John--

All the backfill, except for the top 18" or so, will be 3" to 4" river rock. No dirt. The blocks sit on a bed of gravel which sits on top of the cliff. Still, being able to not worry about it forevermore is a big deal.

Redesign.

--Bill
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seal killer
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Re: Drilling Concrete

Post by seal killer »

All--

Does this design relieve the fill-pressure on the right stack of blocks sufficiently? Each block is 2'x2'x4' and the fill is all 3" - 4" river rock. The slope is from the house towards the cliff and is easily great enough to drain through the river rock.

06-14-18 Design 1.jpg
--Bill
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BadDog
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Re: Drilling Concrete

Post by BadDog »

I'm not arcytek or injuneer, but if they are not locked solidly together, I don't think that helps much, and not at all for the top 4'. Even a deadman anchor isn't going to help much if the stack isn't strongly connected together, or replicated at each level. I've seen mortar stacked block retaining walls blow out at the bottom with an anchor near the top. Then again, these blocks are different. Dunno how that all fits, but I don't think I would be inclined to do it that way unless I was going to concrete them in...
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seal killer
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Re: Drilling Concrete

Post by seal killer »

BadDog—
Can you see that 2.5” high ridge running lengthwise atop each block in the photo I posted? Is that sufficient—iyop—to lock them in? (And the coresonding grove in the bottom of each?)
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BadDog
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Re: Drilling Concrete

Post by BadDog »

I don't think so. It may resist displacement, but won't stop toppling or leaning. If they are not locked horizontally, they will likely act effectively like independent walls moving separately. The only resistance to toppling will be by shear weight across their width, assuming the base/foundation itself is effectively rigid. So the multiple walls do provides some additional resistance to toppling, but IMO not enough. At the very least a deadman between the top and second, and somehow keying in that bottom block so it doesn't displace would be about the minimum I would think. But take that with a grain of salt, it's just my seat of the pants lay shade tree guestimate...
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seal killer
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Re: Drilling Concrete

Post by seal killer »

BadDog and All--

I understand. I should have said that those blocks also have the same ridge on one end and the grove on the other. Might that tend to lock them in horizontally?

In any case, that design requires 60 blocks. At 2,400lbs each, that's 72 tons spread over 144 square feet a few inches diagonally off the corner of my foundation. It doesn't SOUND good.

I'll come up with Plan C and get back to you and everyone.

Thanks.

--Bill
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Russ Hanscom
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Re: Drilling Concrete

Post by Russ Hanscom »

Gravity type retaining walls commonly have an 8:1 or 12:1 batter or slope. Beyond the keys, no additional interlocking is required. Additional layers behind the wall should not be required. If you are based on a rock, that should be good. Perhaps a concrete wedge to set the angle.

Gravity walls are fairly common and stable if done properly.
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seal killer
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Re: Drilling Concrete

Post by seal killer »

All--

I THINK I have talked myself out of the concrete block wall. It needs to be 10 feet tall. If I built that wall in a single row, I COULD deadman it back into the slope by affixing rebar to it, bending an "L" into the other end of the rebar and burying it in concrete in the slope. I've done that with a 7 foot tall, single row tie wall. (That was in 1994. It's still there and still straight.)

If I constructed the wall as shown in my drawing above, it would weigh 72 tons. Although I am confident of the ledgerock that the house sits on, it would keep me awake at night thinking about 72 tons sitting in 144 square feet of area out on the corner of that ledgerock. (Today I'm going to find my grandson's Legos and try to design a lighter version of the concrete block wall.)

Maybe I will build a tie wall. To reduce the pressure against the tie wall--or the concrete block wall, for that matter--I won't backfill it with 3"-4" river rock. I will stack large rocks that sit on the ground on the backfill side up to about the 8 foot level (using smaller rocks on the way up to that level) such that the weight is not against the wall but on the ground. Then I will cover the rocks with the 3"-4" river rock and then finally a layer of topsoil.

The existing slope will drain the entire thing parallel to the wall. Although I have not indicated it, I believe it to be about 6*.

Fortunately, I have two people on site that can advise me: My general contractor, who has almost immediate access to an engineer and an architect and, perhaps even better, a friend of mine in the area that builds these walls for a living (among other things).

Still, this is my "go to" source. I have always appreciated the help I've obtained here and lamented the fact that I am ill prepared to repay it.

--BIll
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