Local failure ( Edge punch failure) of tank foundation

[civilsnc]

I know that for tank foundation, to prevent the edge failure under load of roff and wall of tank at the circumference, thicken gravel ring or earth/concerte ring always put in. For concrete ring wall, it has reference in API 650, but any reference to calculate the thickness and size of the thicken gravel ring for gravel ring for punching shear?

Tony

 

[civilperson]

What you think you know is not universally true. Lots of tanks,(probably the majority), have just a gravel pad under the tank that is uniform thickness and extends five or so feet out beyond the wall. The wall has a steel base plate under it to spread the roof/wall load.

 

[BigH]

civilperson has expoused what I have been trying to get across for several years now. CivilSNC - for interest, you might look up Bjerrum's paper on edge failure of an Norweigan Oil tank (London ISSMFE Conf, 1957). Very interesting.

 

[oldestguy]

Not fully sure of your question. However, if the site is such that an undercut of poor material is required, to be replaced by compacted gravel, be aware of the influence that the load of the tank has out beyond the tank wall.

I once investigated a grain bin of about 80 feet diameter and pretty high which failed due to the edge settling.

The preparation of the site, with removal of the poor material and replacement with good compacted fill stopped at the outside diameter limit of the bin. There even was a sizable thickened edge of the slab.

You can imagine the mess when the bin full of corn ripped open. It even knocked a railroad train off the tracks.

The moral, do the fixing out to a goodly distance outside the tank. I'd not stop until beyond equal to depth of the fix, measured at the base of the hole.