Verification of allowable soil bearing capacity

[dewins]

Soil bearing capacity (say 200KPa) is always stated on design criteria, specification and drawings. Do we need to verify for each foundation, if not, what is standard reference for this?

We normally perform PBT for foundation of buildings. What test is applicable for series of isolated foundation with about 3x3meters in area?

 

[TLHS]

Someone should be verifying the assumptions. If they're low values and being used for an insignificant structure, that might just involve a qualified person coming out and looking at the bottom of the hole before you pour. If you're building a 200 story building you might have hundreds of bore holes, lab testing, a team of geotechsand foundation load tests to confirm everything.

That may or may not be your responsibility though. Even if it's not your job, it's good to flag it if you suspect nobody's doing it.

 

[civeng80]

Agree with TLHS.
A pocket penetrometer is always handy to have, or a simple shear vane test for the "low hazard to life" category structures.

 

[dewins]

TLHS, the EPC contractor based their allowable bearing capacity (design criteria) from the conducted soil investigation during planning stage.

Is there a code reference to require them to perform foundation load test?

 

[kirei17]

soil bearing capacity?
i get the impression that your design is shallow foundation.
shallow foundation is related heavily to the soil types below the designed area and the width and depth of foundation and groundwater level. i usually get troubled if it is multi-layered as it requires an extra attention. i usually consult with a senior geotechnical engineer for this.
it is simple to predict soil bearing capacity for shallow and small sized foundation, just as civeng80 say, but it's not easy to test it for large foundation with large loads. In fact, i don't know if there is a method to that.
For pile foundation though, you could just conduct pile load test with 200% design load.

 

[oldestguy]

While it usually is not necessary to double post on this WEB site, I think you might be interested in the comments from geotech engineers if you post under that area. In my experience those specializing only in structures do not venture into the geotech field much.

 

[JStephen]

dewins, it would depend to some extent on what you were building, the loads, and the spacing. If you had a number of small footings in the same area where the borings and recommendations were done, and similar loading and size to what was covered in the original soils report, it would be reasonable to use the same bearing. If they're scattered out across the county or completely different from what the soils report anticipated, that's different.

Most of the soils reports I see also have recommendations similar to the above items, to the effect that excavations be observed by the geotechnical firm prior to pouring.

I don't know if there's a limit as to how big/small something has to be before it would be exempt from those kinds of recommendations. The building codes used to have presumptive bearing capacities, fairly low, that could be used without a soils report, and I don't remember if that is still in there or not.