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RE: Downdrag on cast in place drilled piers (caissons)[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Downdrag on cast in place drilled piers (caissons)
- From: "Sprague, Harold O." <spragueho(--nospam--at)bv.com>
- Date: Mon, 22 Sep 2003 16:15:40 -0500
You are correct. I failed to mention the overdrilling, and placement sequence. It has been a while since I did this, and bentonite drilling fluid was not considered a hazardous material at that time. In our application, we did not pull the sleeve. It was just left in place. In any case, the formed surface is relatively smooth, and the coefficient of friction is very small.
I have been EOR of projects where a bentonite slurry for drilling fluid was used due to problems with caving soils. However, the bentonite drilling fluid is now considered hazardous waste in California, it must be collected and hauled off site for proper disposal. As you can imagine this is no longer a cost effective alternative for drilling contractors. What is used now is a polymer drilling fluid that does not have the hazardous waste issue of bentonite. If I remember correctly the polymer fluid is mixed with Clorox after coming out of the hole which through chemical reaction makes the mixture benign enough to go into the storm drain.
While you did not mention it in your example, you must drill an oversize hole, install a smaller diameter sleeve, reinf. and pour concrete then pull the sleeve. This is how I visualize having a void around the caisson shaft for placement of the bentonite slurry.
This is an interesting idea, I'll have to look into the coefficient of friction between a drilling fluid left in place and the concrete surface...and of course convince the soils engineer.
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