Crush stone foundation for oil storage tank

[gwkwong]

I wonder if there is any paper that discuss the concepts in choosing the thickness of the gravel require for the large fixed roof oil tank foundation (Dia > 58m, Height ~ 18 m)with internal columns. (no concrete ring wall)

 

[BigH]

If I remember right - we used to use about 1.5 m in thickness and extend 3 m or so beyond the edge of the tank - but really depends to a large extent on the nature of the underlying soils. There is a paper by Brown (in Canadian Geotechnical Journal - 1965 or so) that talks about tank pads and I'll post the details within the next 24h. I'll try to look it up (I'm a member and can check out the back issues). Also see Bjerrum's paper in the 1957 ISSMFE conference (London) - might be important if you are founding on clays - especially with a bit of desiccated crust. On your crushed pad, make sure you use 75 to 100 mm of crushed fines (sand sized) on top of the gravel before laying down your tank plates. This is to prevent "hard spots" that the plates might lie on which could lead to quicker corrosion. Can lay wood planks down during construction.

 

[BigH]

The reference of Brown is: Brown and Patterson, "Failure of an Oil Starage Tank Founded on a Sensitive Marine Clay", Canadian Geotechnical Journal, vol. 1, no. 4, Nov. 1964. In their paper, the pad was 3 m thick - but it wasn't the cause of the failure. It is a good paper and I recommend anyone to find it and read it - along with the Bjerrum and Overland paper I mentioned earlier.

 

[gwkwong]

Thanks BigH, I will try to find it. But based on the stress analysis both for the shell and the column, the stresses degrade rapidly especially at the shell location (since the footprint of the shell is small). We certainly have to compare with the bearing capacity of the native soil, but yet at the shell location base on the stress result we only have to use 2' to at most 3' of gravel. However, being conservative and experience, we usually ended up using 4 to 5' of gravel.