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Looking for Ideas for an excavation

5028 Views 26 Replies 13 Participants Last post by  Upchuck
I am getting ready to bury a 10,500 gal water tank for a fire suppression system. The tank is going in the ground 9' from an existing building, the top of the footing is 5'8" below grade(1 foot footing). The dimension of the tank is 13'2" top to bottom, with either 12" of stone under it or on undisturbed soil, there is a 4' round sump station located 5-10' away from it/building that is 4'8" deeper than the bottom of the tank.
My question is this: the tank was supposed to go in back in the early part of sept when the water table was much lower, but the engineers and precast co have been redesigning if for the last month and a half and the water table is up substantially, finish grade on top of the tank is 410' and the water table is at 394.
I need to make sure that the building does not shift but with the water up I am worried about the 45* slope leading up to the existing footing is going to undermine. Driving sheet piling will cost 22K, I was going to underpin the corner originally, but with the water up that doesn't seem like a good idea. I obviously will de water and drop the table some, but am nervous about the proximity of the building. It is up to me for BMP to design the support.
Any ideas?
to add insult to injury the engineers wont answer the questin how much ground cover over the tank.:laughing: I guess it is not that important

Thanks in advance.
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...a 10,500 gal water 13'2" top to bottom...[and]a 4' round sump station.....4'8" deeper than the bottom of the tank. My question is this: the engineers and precast co have been redesigning it...Any ideas?
What is "it"? A 12' diameter precast manhole with an anti-flotation base? A vault? If I'm understanding right you need to dig a hole about 18' deep only 9' away from a 6' deep footing.

I just got a quote for a 30K gallon fiberglass cistern from here . It seemed reasonably priced. A 10K model might save you several vertical feet of excavation and eliminate the need for a big crane. Maybe you could stick-sheet the excavation with timber walers and random width boards and leave it in-place upon backfill? In decent soil you oghta' be able to that pretty quick.
Paraphrasing something I read somewhere.......
Architects know a little about a lot. Engineers know a lot about a little. Contractors, by virtue of their working closely with architects and engineers, know less and less about more and more until they eventually know nothing about everything.
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