water in borehole

[Hutten]

We are inspecting 18" diameter boreholes for a concrete pour for a pier. There is some standing water at the bottom of the hole. Can someone direct me to a specification for allowable depth of water without a tremmie. They are just pouring down the hole with a chute.

 

[Ron]

Concrete should never be placed in water without a tremie. Even a few inches of water will add gallons to the concrete, thus reducing its strength quite a bit at the bottom and causing segregation.

 

[dik]

Yup... the concrete should be placed into the 'mass' of the existing concrete so that just the exterior concrete surface is exposed to free water...

 

[Hutten]

Yes. Thanks. Drilling contractor indicated there was a spec that I didn't have...

 

[oldestguy]

Look up a paper by Clyde Baker of STS Consultants, Chicago. He studied this condition in Chicago caissons. He determined that anything more than an inch or two will drastically reduce the end bearing capabilities.

I don't recall where it was published but try ASCE first.

 

[Drumchaser]

Hutten

(from FHWA)

If the shaft excavation is not completely dry and the concrete is placed by free fall, then there will be
mixing of the concrete with the water which is present at the base of the shaft. The result would be a
concrete mix with excessive water or perhaps even a zone of washed aggregate if a substantial amount of
water is present. The contractor can often pump out water so that an unobjectionable small (less than 3
inches) depth remains, and this method is sufficient so long as there is not a substantial inflow of water.
In general, a flow into the excavation producing more than 12 inches of water per hour (1 inch per 5
minutes) is considered excessive.