How to determine the position, size and length of existing piles!? 1

[markomarko]

We have recently done the design for the new three storey extension to a small single storey building, assuming that the existing footings are simple strip footings (as indicated by the trial pit survey). To our surprise, once exposed, these turned out to be ground beams to piled foundations! We have attempted to search the council archives to obtain information about the original building but with no success.

Is there any geophysics or similar method method to determine the position, diameter and length of the existing piles, so that we can determine their capacity!?

The site is located in south London, so if anyone here can do this, you are more than welcome to take on the job!

 

[msucog]

markomarko, there are ways to try to identify the details you need. however, it will NOT be perfect so you should understand the uncertainty involved on the front end. one approach would be to expose the top/side of select piles then perform Pile Integrity Testing (PIT) or maybe even parallel seismic. since the tip is fixed, this makes the methods more difficult to perform. PIT can give you an idea of the length and continuity of the piles. since it's exposed, measure it for diameter. if parallel seismic is employed, you could end up gathering some data about the subsurface materials when the hole is drilled. parallel seismic would help confirm both soil parameters and pile toe elevation as well as tip bearing coniditions. there's also some other methods you can employ to try and map the foundation. i've done this for similar situations and selected a few locations depending on the project budget. with limited data, we leaned toward the conservative side and fully disclosed to the owner that there is risk with doing this because of the uncertainty with our assumptions unless we expose every single pile or simply tear the building down and start fresh. either way, to map the foundation will not be cheap but it'll likely much cheaper than tearing it all down.

feel free to ask questions and i'll reply as i can. if you need a few specific details, email me at my g-mail dot com account. my user name is my email.