Pile Cropping
Debond, Debond, Debond!
An interesting loop hole/oversight, that we have come across on site. The main bars for the pile cage are de-bonded using foam down to cut off level.
The designer will never approve foam all the way down to cut off level in case of any drop in the reinforcing cages. (They allow 50-100mm). The piling subcontractor have a tolerance of cage level of -50mm and +150mm in accordance with the ICE Specification for Piling (SPERW). In this case, we have both extremes of +100mm and +150mm, which has resulted in 250mm of bonded concrete.
Normally, this would be easy using a pile cropper or diamond drilling company but not when it is bonded. Back to pneumatic picks by hand.
The drawings and tolerances were all checked by the piling subcontractor, principal contractor, designer and client’s representative. All failed to spot the issue, myself included. I would expect the piling subcontractor to be fully aware of the issue but again nothing was mentioned.
Contractually, nothing that we can do. The pilers are within these individual tolerances. Unfortunately, it falls on the next subcontractor to work through the issue. This means a lot of time and especially Hand Arm Vibration (HAV) as they work around the main bars.
The lesson here is even though the tolerances may appear acceptable in isolation. The sum of these tolerances have resulted in extra time, cost, and H&S risk.
Holdfast Training Services Trial Blog 
Andrew, we had similar issues with debonding the pile over-pours on my site. The contractor was trying to use a chemical pile breaking system which failed on a number of occasions. (See earlier blog post on Recepieux).
It seems pile cropping issues are a recurring issue. There are some mechanical and chemical options but aren’t always suitable due to pile diameter, access or code requirements. If Vibration is a concern there are remote breakers but they may struggle to access the centre of the pile.
Best of luck in finding a solution.
Andy,
I’d agree with Mark above, there are remote demolition robots which are used on my site as part of the demolition package, but they will struggle with the intricacy you require. For any elements which require hand breaking the demolition sub-contractor one of the Hilti breakers, which have lower HAV ratings, allowing longer daily use (up to 8hrs per day).
See https://www.hilti.co.uk/content/hilti/E1/GB/en/products/drilling-and-demolition/breakers/world-of-breakers/avr-for-breakers.html for more information
I continue to be amazed at our inability to achieve better tolerances. If we can get to within -50mm why not also +50mm? We can design this variation into the pile cap and so avoid any hand breaking. How much would it really take to deliver this as opposed to time spent breaking out?