Shaft Coring Experience

[mehr27]

We are planning to core through existing 60" drilled shafts and insert smaller 30" shafts. The original lengths are not long enough. I'm looking for any feedback with this procedure - positive or negative experiences, risk of drill bits breaking, anything at all. We have investigated other options and am trying to put together a solid argument to push this method as our remedy.

This is similar to thread274-233058.

 

[TDAA]

Your looking to do 30" cores through how far?

How old is the concrete?

I guess what I am wondering is why was a 60" pile used, when a 30" will apparently work? It also seems that perhaps abandoning the 60 in-place and offsetting, or using a group and pile cap would be a quicker fix. Just wondering, since you seem to have a reason to go this way.

 

[PEinc]

Also, it might be cheaper and easier to replace or supplement the caissons with micropiles - either adjacent to or through the caissons.

http://www.PeirceEngineering.com

 

[mehr27]

The core depths are around 20 feet each. The existing 60" shafts were built six years ago and estimated for future use. We looked into offsetting the footing but there are some negative impacts that led us away from that method (ROW, traffic control). Have heard from others as well that micropiles sound like a good option. Any other thoughts about the cored shaft idea?

 

[emmgjld]

I was involved in a remedial job which required coring a 6"-8" hole through a 18' long 18" diameter pier so a micropile could be installed.
Not terribly difficult & went without a hitch.

Actually the micropile could have, and should have, been drilled without the coring and would have saved time & money. The Structural and the Architect had virtually no previous experience with this sort of thing and complicated the entire operation. Experience Counts.

 

[Zambo]

emmgkl,

you mean just drill through the existing shaft with a rock bit and then continue drilling through the soil beneath and when reaching the required depth install the micropile?


mehr27,

so the piles (shafts, casissons..) are only 20' long, not very deep. I would prefer to look at removing them and starting again with a completely new foundation.

 

[FixedEarth]

You have a robust pier with a lot of capacity. What is the reason for the remedial work? Have you verified capacity through load testing prior to this repair?

 

[Ron]

FixedEarth...that was my thought as well. From the description, it sounds like it might be a drilled shaft for a traffic control device or sign.

20 feet is a bit short for a 60" diameter shaft. Proportions seem a bit off.

As for remediation, if you are going to attempt drilling down the center, you could as easily drill immediately adjacent to the shaft for micropiles and still keep your footprint at about 84 inches.