BIG ROCK PROBLEM????

dirtworksequip · Jan 6, 2007

CHARLZ, good points on the support. I may try and move it again if the ground freezes. Right now its rainy and just too soft and muddy.

Do you think some concrete piers would work? I could auger 9 inch holes into original ground and then place Quik-Tubes or Sono tubes and pour concrete. I may even be able to get an extension for the auger and go another 18 inches. About 4 feet in the ground with the rest of the pier above the existing grade. Then fill with dirt above the piers(to protect the piers while resetting rock) and try to get it set back into place.

pat32rf · Jan 6, 2007

I don't think that 8" sonotubes are going to give you much in the way of lasting support, especially if there is any clay content to the soil. Just finished a 10x16 deck, the bldg dept wanted minimum of 4-ten inch tubes, down to below frost(48") in clay soil. You can get a new style tube called a "Bigfoot". Shaped like an upside down mushroom, about 4 times the support area.
Don't suppose it gets cold enough in your area to freeze that pond?

dirtworksequip · Jan 6, 2007

Pat32rf, yes the pond will freeze some winters. Thanks for the heads up on the 8" tubes. What about pouring 8 or 10-8" tubes and then placing some sheet steel (4'x8')on top of the piers with the rock sitting on the steel sheet? Just a thought. Do you have any other ideas as far as getting it to stay where I reset it?

EddieWalker · Jan 6, 2007

I'm wondering about the practicality of using tubes. Your flat rock sunk in the groud from it's weight. With all that surface area, it sank. This really boggles my brain, and I'm not getting how a sonotube is going to do anything. I don't understand what you'd do with a sonotube?

They are for bringing concrete above grade. If you drill some post holes and fill them with concrete, then what will this accomplish? The flat rock sank in the ground with all it's surface area. What will a few sonotubes do? Where will you put them?

OK, the rock sank. The rock is flat and it sank..... The rock has allot of surface area and it sank....... I think you need more surface area.

You have the trackhoe. Why not dig a trench perpendicular to the rock. Make the trench go under the rock and extend it out into the field on either sides. I'd got two feet deep. Then I'd dig another trench just like the first one, but four or six feet away from the first. And to finish it off, dig three more trenches connecting the ends and middle to creat an sqare looking 8.

Put in plenty of rebar and tie it all together. Pour concrete to within four inches of grade. Let it dry for a week or two, then push the rock on top of it. Cover the rest of the concrete with dirt and smooth it out.

The bigger you make the 8 shaped footing, the more weight it will hold. The more surface area, the more strength.

Good luck,
Eddie

charlz · Jan 6, 2007

Yeah, concrete 'tubes' would just get driven into the ground unless they go down to something solid, like bedrock. If you think about it all you are doing is taking the wieght on the top of the tube and moving it to the bottom. If it is the same type of soil/dirt it won't help any. The 'mushroom' mentioned above might help.... but then I am not an Engineer so take all of this with a bag of salt

With the abutment I was thinking more of trying to keep the rock from eventually tipping and sliding into the water. The dirt under the overhang has a place to go.. down and out. Couple this with erosion from rain water, melting snow etc. and I don't think it would take all that long based on what the soil looks like in the pictures.

As Eddie noted if keeping the whole thing from sinking is a concern you probably need to take that weight and spread it out over a larger area. Really depends on your soil, it may settle some and thats it. But I think it would always be prone to sliding down into the water without something to keep the dirt under it.

Charles

CurlyDave · Jan 6, 2007

If you think about it all you are doing is taking the wieght on the top of the tube and moving it to the bottom.

Actually piers work on a different principle than footings.

With footings the weight is transfered to the earth by compression of the soil under the footing.

With soft soils, piers must be used. The force is transmitted to the earth by friction on the sides of the piers.

While I understand why dirtworksequip wants the rock where he has it, I am not convinced there is an economical way to do this.

If the soil is too soft, short concrete piers will not do much good, they will just increase the weight which must be supported. Similarly, a steel plate will increase the weight. Now if the plate is larger than the rock, then you might spread the load, but I think it will take a pretty large plate to produce a solution which is stable over time.

I suspect you need to talk to a soils engineeer, and then a civil engineer.

BTDT · Jan 7, 2007

Once you get the rock out of the way, put down 4 piers however deep you can get them. Two as close to the edge as you feel comfortable, then 2 back about where the back end of the rock will be. The top of these need to be below grade 6 or 8 inches. Then get you some steel I or H beams that extend a couple feet out in front of your piers near the water, and 6 or 8 feet behind the end of the rock. Fill dirt around beams, the top of which should be a couple inches out of the dirt. Put rock on top of beams and push toward water till it gets where you want it. Then cover and fill in as needed to hide beams and close gap around rock.

dirtworksequip · Jan 7, 2007

Thanks, guys for the suggestions.
Eddie, I understand what you are saying about the figure 8 footing, but I'm not sure that there will be enough area out on the peninsula for it. I'll keep that in mimd as an option though. Also have to figure the cost of the concrete. If I want to spend that much. Maybe curly dave is right. No economical way of doing it.
I was going to auger the holes and then pour the piers to the grade I needed the bottom of the rock to be. Which is slightly above the existing dirt grade. The dirt gets lower the more I mess with the rock.Then fill and compact the dirt to just above the top of the poured tubes. I thought the multiple tubes would give more bearing strength to what the rock was setting on. Maybe I just need to forget it though.
I don't know that the rock really settled or the ground towards the front eroded away and caused it to settle.

What does anyone think about digging a footer 3 foot deep and then compacting crusher run stone in the footer ditch. Would that give it more support than just dirt?

Keep the suggestions coming. I appreciate everyones imput. Thanks again!

Regal · Jan 7, 2007

The force is transmitted to the earth by friction on the sides of the piers.

I agree with what Curly Dave says, however, I think that if you move the rock and pour piers, when you try to slide the rock back into place it will exert too much side push on the piers and possibly cause them to crack or break off. Raising the rock and pouring piers would be best but don’t know how you could dig holes with rock in the way????
This is one of those times your “between a rock and a SOFT spot”

charlz · Jan 7, 2007

CurlyDave/Regal,

Thanks for the info on how piers work, I hadn't thought of friction on the sides.

Maybe the thing to do is re-work the rock and dirt the way you want it and then figure out if it is settling or tipping or whatever. Might be that it moves so slowly we will all be gone before it becomes a problem

So how would your figure that out? Drive in some rebar here are there around the rock that are level with the top/bottom or some chisel mark so you can reference this in a year or so and see what is going on?

This way you would know wether or not you have a problem before deciding to spend $$$ to fix it.

Charles