interpreting skin friction graph from geotech
interpreting skin friction graph from geotech
(OP)
I usually just get one value of skin friction from geotech that I multiply with pile circumference and length.
This time I got a graph instead.
Am I right that for every feet there are abrupt changes in skin friction values.
Say at around 25 feet, I'll multiply 1 feet of the 25 feet by 600 psf and another 1 feet by 250 psf, and so on then add them?
This looks like simple math but I'm surprised with the abrupt changes in skin friction per feet.

This time I got a graph instead.
Am I right that for every feet there are abrupt changes in skin friction values.
Say at around 25 feet, I'll multiply 1 feet of the 25 feet by 600 psf and another 1 feet by 250 psf, and so on then add them?
This looks like simple math but I'm surprised with the abrupt changes in skin friction per feet.







RE: interpreting skin friction graph from geotech
RE: interpreting skin friction graph from geotech
But, maybe they really did test the heck out of it.. or they took a bore exactly where you plan to put your one pile.
RE: interpreting skin friction graph from geotech
RE: interpreting skin friction graph from geotech
RE: interpreting skin friction graph from geotech
As for what to use for design, depends on what you are designing and how much settlement/movement you can handle. Only you and the geotechnical engineer working together can determine that.
Mike Lambert
RE: interpreting skin friction graph from geotech
but can i use this data though instead of the "average"? it's not complicated to assign a skin friction value per feet or 2 feet from this graph?
RE: interpreting skin friction graph from geotech
delagina - Sit down with geotech (per GeoPaveTraffic's comment). Find out all the details of the soil at the 18' to 25' depth. If my hunch is right, you may be able to get point bearing on some lightly loaded short piles.
Note: I'm not saying that this will work... I am saying that a meaningful discussion with the geotech is well worth the effort.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: interpreting skin friction graph from geotech
I have seen this by others for footings and even for end bearing on piles and that gets even more weird. For spread footings at 1.5 m you can have 325 kPa bearing, but at 1.7 m you can have only 250 kPa, yet at 1.9, it is back up to 350 kPa. I doubt very seriously that they took into account zone of influence.
RE: interpreting skin friction graph from geotech
RE: interpreting skin friction graph from geotech
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: interpreting skin friction graph from geotech
BA
RE: interpreting skin friction graph from geotech
RE: interpreting skin friction graph from geotech
He cites FHWA - HIF-07-03 which I couldn't find. I did find HIF-07-039 but that doesn't relate to geotech reports (its for augered pile design)
FHWA NHI-10-016 is for LRFD Design of Drilled Shafts and does have info regarding the geo report (and I highly recommend it as a free resource for anyone who designs drilled pier foundations):
"Once the data from the field investigation and laboratory testing program have been obtained, the
geotechnical engineer is responsible for reduction and interpretation of these data,..." - pg 2-3
"A geotechnical design report, also called a foundation report, typically provides an assessment of existing
subsurface conditions at the project site, presents geotechnical analyses, and provides appropriate
recommendations for design and construction..." - pg 2-24
"For each geomaterial layer established in Step 11-1 and for each limit state identified in Step 11-2,
assign the appropriate geomaterial properties needed for evaluation of axial resistances." - pg 13-4
If you haven't reviewed this guide before, I suggest you give it a glance through before completing a deep foundation design.
http://www.fhwa.dot.gov/engineering/geotech/librar...