DRILLED PIERS INSPECTION 4

[Robert222]

Can anybody explain me how to inspect drilled piers reinforcement before concrete placement?
Spread footing foundation inspection is pretty straight forward, but how can i see and check rebars inside the drilled hole?
Thanks.

 

[hokie66]

Inspect the cages before they are lowered into the hole. Then, provided you have a sunny day, use a mirror to reflect the sunlight into the hole.

 

[Robert222]

So should I request to remove the cages from the holes if they are already lowered? On the plans is specified to call for inspection before concrete placement which is fulfilled...the contractor will kill me if i will request to remove all 30 cages...
The piers are 18ft deep....

 

[JAE]

I've usually verified the following:

1. That they used the correct number and size of vertical bars.

2. That the hooping or ties are as specified.

3. That the vertical bars extend out of the pier top the required distance to properly lap with the future upper reinforcement.

4. That the vertical bar cage is provided with the required clear distance from the hole face (usually 3").

5. That the bottom of the pier is clear of excessive debris, loose dirt, etc. (i.e. it should be cleaned out well.

6. If required - verify the base of the pier is on the expected soil strata - this can vary greatly from site to site - read the geotechnical report. Sometimes piers are simply founded at a set depth (your 18 feet), or based X distance into a particular type of material (such as 3 feet into blue shale).

Usually with items 1, 2, 3, 4, and 5 you can do this with a mirror (per above suggestion) or a very high powered flashlight. Item 6 is usually performed during drilling - and many times the geotechnical engineer is hired to validate the pier depth.

 

[hokie66]

Yes, I didn't mean to force the contractor to take out cages already in the holes. But there are probably some more which you can inspect while they are horizontal, and as JAE say, you can check the bar sizes, hoops, and spacers from the top.

 

[henri2]

JAE has pretty much summarized the main points for you. If you want further information check the following:

1. ACI 336.1-01: Specification for the Construction of Drilled Piers

2. DOT Drilled Pier Inspection Manuals. Example:

http://www.ncdot.org/doh/preconstruct/highway/geotech/formprovdet/BodyandFAQ.pdf

In some jurisdictions, if the cage has been lowered prior to the inspector's arrival, the contractor is required to take the cage out so the inspector can perform a visual inspection.

 

[JAE]

Just a humorous side note - some years ago I worked down in south Texas for a firm that had been instrumental in the development of belled pier designs - working with "the man" Terzaghi. They had an old photograph of a foursome of men sitting at a card table, playing cards, drinks on the table, smirks on their faces, etc.

The whole group was situated at the bottom of what looked to be a huge belled pier bottom - shaft perhaps 10 feet and bell much larger. I wonder if the photo is out there on the net somewhere. I'd love to get a copy.

I don't think they were inspecting the pier - but perhaps already had done so and were taking advantage of the cool air and shade.

 

[BigH]

JAE - one of my first jobs was to inspect installation of belled caissons being placed for uplift of very high high-voltage power transmission lines. It was cold . . . inside the caisson it was warm. Guess where we spend a good portion of the time making sure all the "loosened" material was removed from the base . . . (and on a tension caisson, too!).
Unless you go down into the caisson, it will be very difficult to tell if you have "muck" on the bottom - or not. There are, of course, methods to determine this - or perhaps the design "ignores" the base loading (not usually with bells).
Today - we have gone into caissons before lowering cages (if required) - but you'll have to make sure you follow confined space protocols.

 

[msucog]

geotech should check foundation/bottom and/or construction operations during drilling depending on foundation type. check rebar before lowering (or in place if you are able to effectively inspect). what building code does the project fall under? if it's IBC, then foundation soils, rebar and concrete should all most likely be checked/tested/signed off on. good luck

Ryan Coggins, P.E., S.I.

http://www.linkedin.com/in/ryancoggins