Biofilter tank foundation on 2:1 slope 2

[strengineer17]

I need to design a foundation for a 41000lb tank on a 2:1 slope. At first i though a frost protected slab on grade would work but then too much fill would be needed and there is a river behind which limits how far out i can go. Should i just make a square foundation wall that goes all the way around the box? The slab will be 10' X 16' and the tank has an 8' diameter. Any help would be appreciated.

 

[civilperson]

Build a good soil pad of 95% compacted optimum moisture select structural fill over the area of the tank plus five feet in all dimensions, (18' diameter), at least three feet thick and then place two foot of compacted crushed rock. This should suffice if the native soils under the structural fill have nominal strength. This fourteen foot high tank will load the soil to less than 500 psf if the slab extends 2.5 feet outside the wall.

 

[dirtygeo]

Is the tank at the top of the 2:1 slope? part way down? What is at the bottom of the slope? Slope stability/failure would be the major concern here and greatly dependent on soil conditions and site layout. How high is the slope? Is the toe eroding? More info needed.

Dirtygeo

 

[strengineer17]

The toe of the slope leads to a small river. The base is located at the top of the slope. The horizontal distance to the water is approx 50'. The soil is a silty sand material. I think i may put the slab on foundation walls and footings that extend five feet down, for frost protection. However if anyone has a better idea im listening.

 

[BigH]

You might want to take a look at the IBC requirements for set-back of foundations on slopes for some guidance - but, still, you should compute the allowable bearing capacity of your tank on/near the slope as per methods described in Bowles (Meyerhof, I believe) or other such texts/manuals/books. The way to put the tank on a granular pad is the way I would go and civilperson gave you a good description. Make sure that you do not have the bearing affected by the proximity of the slope.