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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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How big is this tank?

Width and length, already know it is 13'2" tall. I am guessing 10' wide x 12' long x 12' high internally.

How much area is there to put in a tank?

Just wondering if there were space constraints, and that is why you went with a precast tank. If there is enough space I would have gone with Xerxes or Containment Solutions fiberglass tank. Then you wouldn't have to go quite as deep, and much easier to install.

Also is this a drive-on tank. Strong top able to take the weight of a vehicle driving over it, or are they going to do something so this could never happen.

What kind of soils?

This answer will help with your question, and I would use a slide rail shoring system instead of sheet piling. A lot less money to rent and you slide it down and add panels as you dig it out, and no need to slope the excavation.
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At least you will have the narrow end of the tank by the building. But I would still use a slide rail system to minimize excavation, if you slope it that is a lot more dirt.

Found this video that shows a typical slide rail system. They also make a clear span sytem without the roller bar in the middle for long excavations that require a upright in the middle.
I thought that same thing. Thats why I wouldn't do this without some type of very sturdy shoring all the way to the top, no sloping. Sometimes that stuff is like digging in a bowl of marbles. We have a lot of that around here.
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