Cleaning Belled Piers 1

[Qrs]

How are the bells in belled piers cleaned out? I saw a patent for a belling tool that collects and removes the dirt as it drills. Is this typical? Or is the loose dirt removed by hand? (people and buckets?) I'm new to belled piers and want to learn what the typical practice is.

 

[oldestguy]

Nobody likes to go down there. However, for a belled caisson, I'd never do it. There is a good chance for the sides to cave in on the "inspector". So, we try to examine the bottom from the surface. One excuse I have heard (and have had to accept) is assume that a certain percentage of the bottom is a pile of loose earth that the cleaning tool can't get. My experience is limited to perhaps 10 jobs, so those that have more experience may come up with a good way to approve what is done before concreting. I usually would be the first to go down (inside a casing) to set the procedure for the production inspector. Of course all sorts of safety procedures are needed in case of CO2 and of course passing out. Hand clearing is the best, but there are some contractors that do not do that.

The best person to learn from is Clyde Baker who wrote this manual:

http://www.browntechnical.org/products/Drilled-Shaft-Inspector's-Manual.html

 

[JAE]

We usually rely on the belled tool that the drillers use. I don't believe that OSHA lets workers into shafts unless they are cased.
The leftover scrap soil at the bottom gets "tamped" by the weight of the wet concrete eventually to some extent.

 

[Rockmynci]

As previous posts say, inspection of belled piles (also called under-reamed piles in UK) is carried out from surface now. A couple of companies over here have developed specific tools to visually inspect the base of the pile using a camera. One also allows you to recover U100 samples from the base so any softening can be seen. See

http://www.nce.co.uk/less-is-more/541244.article

 

[BigH]

One of my first jobs was a large belled caisson in Southern Ontario - in tills - so they stood up with no problem. The shaft was cased. We used to spend time there as it was really cold up on top! Times have changed.

 

[hokie66]

On a sunny day, I use a mirror to reflect the sun's rays to the bottom of the hole. Much better than any type of artificial light.

 

[JedClampett]

I thought that a video camera and lights were used to avoid sending someone into a grave.

 

[GeoPaveTraffic]

I have inspected numorous belled piers over the last 25 years, never felt the least bit of concern for my safety. As others have pointed out, current US rules make it difficult but not impossible to peform downhole inspections/cleaning. Nothing beats a laborer using a shovel and bucket to clean the bottom of a shaft, belled or straight. When I prepare foundation recommendations, I provide two options. One with hand cleaning and one for machined cleaned. Needless to say the hand cleaned shafts get a higher allowable pressure.

On a side note, the largest bell I every inspected was 12.5 feet off a 6 foot shaft in shale.

Mike Lambert

 

[BigH]

Mike - mine was 15 ft bells - about 15 to 20 ft down in good Southern Ontario Glacial Till. We found that after cleaning, within several minutes, the upper couple of inches would "soften". As a result, we would clean and get out and place the concrete with some speed.

 

[GeoPaveTraffic]

BigH - 15 feet is impressive! We didn't have any issues with these in the shale. Good material no significant water inflow, you and half-a-dozen of your closest friends could have lunch in these things. Biggest problem was not going too deep into the unit as the target material was underlain by a poorer shale. If you missed the target the shafts would have to extend to limestone bedrock another 40 feet or so down.

Mike Lambert

 

[oldestguy]

One tip I learned a while back. For the mirror and sun technique, use the mirror your wife used for magnifying her make-up. It sheds a strong light with some width. I find it is helpful for the guy down there also.

 

[darthsoilsguy2]

i use a RIGID color see-snake. i tie it to a long rebar with a 90 bend at the head to control it