Tank Settlement Vs. SBC from Shear 1

[marcploks]

Hello!!

I would just like to ask..

is it ok if Tank Load is greater than allowable soil bearing capacity (ex. Tank Load = 18ton/sq.m, SBC = 14 ton/sq.m) as long as it passes allowable settlement criteria?

Thanks in advance!!

 

[motorbiketocrank]

No, it's not ok to exceed the allowable bearing capacity. The bearing capacity is based upon shear failure and settlement criteria, both of which should be met. Having said that, usually the bearing capacity of a tank would be based upon settlement criteria (because shear failure is usually not a problem for a large tank bearing area). So my point is that you need to make sure a geotech has provided the bearing capacity based upon an analysis of the specific loading condition and the soil. (i.e. bearing capacity is not just a function of the soil.....a normal footing and a large tank sitting on the same soil would have different bearing capacities).

 

[marcploks]

Thanks a lot!
This helps a lot!

 

[BigH]

I'm late with a response, but geogdg's response which is correct points out the care in using terminology. We have had a number of threads on this in various geotechnical engineering forums.

It is my view that

1. Any time you use the word "capacity" you are basing your premise on shear strength. Ultimate bearing capacity is as the formulas (whichever one you use) give you - the allowable bearing capacity is the ultimate divided by a factor of safety (usually 3).

2. When one uses, as a premise, settlement or distortion, it should be referred to as "allowable bearing pressure" - usually "net". This clearly defines that the given or quoted value is settlement or distortion driven.

I don't use the term SBC (Safe bearing capacity) - mainly because of the two points above. In most soils, it is the settlement and/or distortion criteria that govern the applied loads.