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Side Friction in Limestone

Side Friction in Limestone

Side Friction in Limestone

Hi Everyone,

I've been trying to find the correct equations to use to determine side friction in Limestone in a Karstic Environment with a 30" dia. drilled shaft.

Initial tests show an RQD of 50% and qu = 5000 psi.

Any insight on the correct formulas to use would be great. I've referenced the FHWA manual and equations 13-18 and 13-19 seem to be what I'm looking for but I want to see what everyone's thoughts were.


RE: Side Friction in Limestone

While not directly addressing side support of pile in karst - you might want to look at a Geo-Strata article by Griffith, et.al., "A Probabilistic Approach to Karstic Foundation Variability". Can give some other insight other than "forumulas".

RE: Side Friction in Limestone

With an RQD of 50, I don't know how much I would want to rely on side friction. Is the qu value from a reassembled section of core, with the joints tacked back together? Or, does it represent the best piece in the run? I agree with BigH, insight other than formulas will serve you well on this.

RE: Side Friction in Limestone

the AASHTO LRFD Bridge Design Specs has equations for it but with an rqd of 50% you won't have much capacity. I'd suggest getting a geotech to give you a value. We will calculate something so we can do some prelim work but always end up getting a final value by the geotech. They always end up with a value much lower than what I come up with.

The soil guys understand it much better than just some equations in a book that anyone can plug and chug. After all they do the borings so they have the info they need.

RE: Side Friction in Limestone

Hi CJ, do a pile testing and I am sure you might get the right answer.

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