Foundation for waste tank
Foundation for waste tank
(OP)
I am designing foundation for a waste steel tanks. The ground condition is 2m soft made ground , over 14m clay (Cu = 40 + 15z) over incompressible limestone. I am thinking of using pile foundation but also considering pad foundation.
Can I design the pile foundation as normal for other civil structures or is there still a risk of edge failure? Is pad foundation feasible in this condition? The base of the largest tank is 1.25 mbgl.
Can I design the pile foundation as normal for other civil structures or is there still a risk of edge failure? Is pad foundation feasible in this condition? The base of the largest tank is 1.25 mbgl.





RE: Foundation for waste tank
I would go for a tank pad foundation of granular - say 3 m or so larger than the diameter of your tank. If the soft made ground is fill and poorly placed, I would dig it out and replace with a compacted river sand - then the foundation pad above ground for 2 to 2.5 m or so.
There is always a risk of edge failure - especially if the clay has a bit of a desiccated crust (while you don't show it with your undrained shear strength profile, it might) But you design to mitigate such risk - in this case, check out Bjerrum's paper in the 1956 London ISSMFE conference. He talks specifically about a tank edge failure.
40 kPa is about 800 psf - I remember several storage tanks we did in years gone by with approximately this Su value. Youi might want to put in wick drains to speed up the settlement (and increase the Su values) - you can take advantage of initial water test loading - load in stages. Would work fine. . .
Don't forget to have flexible connections - you will get long term consolidation settlements (and secondary)
RE: Foundation for waste tank
If I have to replace the fill with compacted sand, we are talking of excavation to about 4m depth with gwl at gl. Although that means founding on Su = 70kPa. The cost of excavation and excavation in dry ground may suggest using piles. Using pile means small and regular settlement which should prevent any differential settlement and damage to tank..
RE: Foundation for waste tank
RE: Foundation for waste tank
The question is do I still need to check for edge failure? Does anyone have a copy of the work by D'Orazio and Doncan? Please pass it to me.