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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 long is this thing? If it is not too long, you may be able to build some sort of shoring by driving a few pilings to prevent shifting. From there, anchor the pilings back towards the building. Erosion is mainly what you would be fighting if the soil is native compacted. If you can keep the bottom from blowing out, you should be fine. Set the tank, and then backfill a few feet at at time. Pull your shoring up in increments as you backfill. Once backfilled, pull the pilings out (could be 3" sch 80pipe with tapered ends). All I can say is I am glad it is you and not me. Precision work and high water tables should not be said in the same sentence.

Good Luck!!!
Drive in some 6x6 posts and stick a road plate in front of them or some 3/4" plywood.
Hey no stealing ideas:laughing: Never mind, I was way more high tech with the sch 80 pipe vs. the 6 by 6 posts. Either way, I think it would work if a guy didn't dink around and leave it open for days.
I guess that they didnt like the number I gave to shore up the excavation.:laughing:
It's funny how engineers often overlook the complexities of performing the work they design. It is also funny that it takes a lowly excavator to point it out in order to cause the design to actually become cost effective.

Why do engineers make the big bucks?????? I was always told it was because they save you money in the long run. I say it is the tradesmen who should make the big bucks, as we are typically the ones uncovering the pitfalls of designs with regards to the financial burden on the owner.

Way to go on the reality check Guyute!!!
Thanks for making that clear Gene. That is one thing that I am good at doing.......playing well with others!!!:laughing: The point I was making was that if the engineer doesn't consult the excavator/builder/etc. prior to the sign off on the plans, things often end up costing more.

I had to replace an entire sewer lateral and pull up the outlet on an existing house, etc. due to an engineer not accounting for proper fall when designing the new main. Not a big deal, but I asked him later why he didn't check any of the as built elevations. His response was that he wasn't worried since you could always just pump it..........this was said right in front of the developer that hired him to save himself money.:clap:

Overall, if possible, work with the engineer prior to starting any project to go over any pitfalls and expensive change orders. I know the tendency is to bash on engineers, but they have their area of expertise and we have ours. Combine the two and everyone wins. Occasionally you have the engineer that can never be wrong, and that is where all you can do is just smile, nod, and document everything. My best friend is a Civil Engineer, so I like to run things by him on a regular basis.
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