placing concrete in wet shaft - how to account for material separation?

[mikeCTE]

a contractor we're doing work for recently placed concrete in a 10ft deep, 3ft diameter shaft for a timber pole foundation. the intent of the concrete is to increase the passive bearing area to the diameter of the shaft instead of just the diameter of the pole, so we're not super concerned with compressive strength of the concrete.

however, the contractor apparently placed the concrete while the shaft was partially filled with water and simply dropped the concrete in from the truck instead of funneling it or tremie-ing it. now, the site inspector is calling the concrete no-good and we're hoping to validate that it is not an issue.

for similar projects we work on (temporary projects), we used CDF all the time to increase passive bearing area. CDF is typically 50-300 PSI material. the concrete used by our contractor here was 2500 PSI material. my thought is that even with some washing of the cement from the aggregate, there's still more than necessary to get the final product to behave like a lean concrete or CDF. however, i will need to justify this, not just claim "engineering judgment". d

does anyone know where i can start? or have a reference for a situation like this? thanks

 

[SlideRuleEra]

The contractor apparently placed the concrete while the shaft was partially filled with water...

The key question is the depth of the water. If it was a few inches or perhaps a foot... maybe two feet, IMHO, you might be able to offer reasonable justification. If it was more water than that... I'd agree with the inspector.

Another question that could (should) come up: Was the pole reasonably centered in the shaft?

If the only person who can answer these questions is the Contractor... I would stop there... who knows what really happened.

Of course an answer can be obtained by coring the "concrete" for it's full ten foot depth and testing the cores. Most likely this is not worth the money and will prove the inspector is right.

There may be a "long shot" way to present reasonable justification, determine if the shaft backfilled with just loose concrete aggregate (no cement) will provide adequate bearing area.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Teguci]

FHWA - Drilled Shaft Manual - Should be able to download it for free.

https://www.fhwa.dot.gov/engineering/geotech/library_listing.cfm

9.3.1.2 - Discusses dry placement with an allowance of 3" water at bottom with low infill flow of additional water. Notes that tremie alone may not be appropriate

 

[oldestguy]

What do the specifications state? Have you checked the earth pressure resistance you actually need? Can the loose stuff down there be compacted, as with Vibroflottion? Cost of replacement may need to be evaluated against other things, such as surrounding with more concrete.