Rock RQD versus Alpha E Values
Rock RQD versus Alpha E Values
(OP)
Does anyone have the values correlating the RQD and Alpha E values for Soldier Piles in Rock Sockets. Any values would be appreciated. Thanks in Advance.
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Rock RQD versus Alpha E Values
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Rock RQD versus Alpha E ValuesRock RQD versus Alpha E Values(OP)
Does anyone have the values correlating the RQD and Alpha E values for Soldier Piles in Rock Sockets. Any values would be appreciated. Thanks in Advance.
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RE: Rock RQD versus Alpha E Values
AlphaE is a function of RQD = 0.0231*(RQD)-1.32 >= 0.15
The reference in HB-17 is (Gardner, 1987). A fuller citation is: Gardner, WS (1987). "Design of drilled piers in the Atlantic Piedmont." in 'Foundations & Excavations in Decomposed Rock of the Piedmont Province', GSP 9, ASCE
I have wanted to track down the derivation of AlphaE, especially as the limit of 0.15 is reached when RQD is less than or equal to about 64%, which limits the utility of the function dramatically.
I am sure that the Linda Hall Library could get you a copy of this paper.
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.
RE: Rock RQD versus Alpha E Values
RE: Rock RQD versus Alpha E Values
Thanks for the reference.
Jeff
RE: Rock RQD versus Alpha E Values
RE: Rock RQD versus Alpha E Values
I'm amazed you use the RQD system with such precision. It is after all an empirical parameter dependent upon a number of things but most importantly quality of the driller who obtained the core and of the person who logged the core. Whether RQD is 63% or 65% will make very little difference to your actual design. I am not too familiar with alpha e but if it is indeed related to RQD as suggested in the formula there is obviously even more room for error and thus as usual, engineering judgement is far more useful than simple number crunching.
RE: Rock RQD versus Alpha E Values
I have the ASCE Rock Foundations Book #16 by the US Army Corps of Engineers. In it on page 28 they relate the RQD value to the in-situ rock modulus of deformation. The RQD has been used for over 40 years. I have read where massive column footings have settled over 6 inches on rock because the frequency of the joints was unknown. I agree a few percentage points is not a big deal but you have to start somewhere. Thanks for the logging and drilling tip. Alpha E I believe is AASHTO's terminology.
RE: Rock RQD versus Alpha E Values
Happy Crunchin' !
RE: Rock RQD versus Alpha E Values
Thanks for the references guys!
RE: Rock RQD versus Alpha E Values
Apparently, the alphaE equation as presented above correlates well with the "best fit" Bienawski's Modulus Reduction Ratio - as shown in the LPILE Plus 5.0 documentation.
Anyone have a source for this figure showing best fit line and scatter data?
Jeff
RE: Rock RQD versus Alpha E Values
I have the 2001 softcover book by Reese and Van Impe called "Single Piles and Pile Groups Under Lateral Loading" and on page 104 it has all the scatter and best fit line.
RE: Rock RQD versus Alpha E Values
RE: Rock RQD versus Alpha E Values
I have a copy of that book - I should have thought to look there as IIRC, Ensoft is Reese's consultancy company. Doh!
Panars,
As usual, you're the goods!
Jeff
RE: Rock RQD versus Alpha E Values
Agree RQD is depndent on driller for good quality of work, but also his equipment. Are we talking E cores,AW, NX, BX, single tube or double tube or wire line?
Any one of these mentioned in those texts?
I'd guess thre might be as much as 50 percent error (or difference) between smaller and larger core diameters and methods.
RE: Rock RQD versus Alpha E Values
Regarding RQD, it is universally considered to be an "N" sized core measurement (i.e., 2-in diameter). I'm fairly sure that it is actually a two-times the diameter measurement, which for 2-in core would be the total length of 4-in or larger pieces, excluding drilling induced fractures. However for "A" sized core if you based it on 4-in pieces, you'd understate the RQD.
I hate to sound ignorent on the AlphaE matter, just don't have that stored in the grey matter. I do have a thesis that has lots of information on rock mass properties.
f-d
RE: Rock RQD versus Alpha E Values
I just finished a rock socket H Pile job with a RQD of 85 to 95%. My lab used a 2-1/8 inch NX core. I beleive AlphaE is based on the ratio's of rock field modulus over rock modulus for a perfect intact lab specimen. I use the Fred Kulhawy Chart to come up with the actual rock cohesion or residual shear value reductions with my actual RQD value. This lab counted the rock that remained in the hole for its RQD value as it was a very hard sound schist/gneiss with mica trace. Based on the grey water I saw coming up and out of the drilled holes it looked like the RQD was going to be very high anyway.
RE: Rock RQD versus Alpha E Values
One way we're getting into trouble with this discussion is an understanding of your ultimate goal. If it's end-bearing on an h-pile into rock you may just be looking at ultimate strength with a safety factor. If it's slope stability, tunneling or something else more detail in the assissment is warranted.
For a better understanding of these things, I'd start with the 1974 publication by Bieniawski and his "Geomechnics Classification".
Now that I've said all of this Kulhawy is a good reference also.
f-d
RE: Rock RQD versus Alpha E Values
I used 0.70 for a HP Soldier Pile/Timber Timber Lagging Design holding back 8 to 10 foot of Lean Clay approx 175 feet long. AASHTO provides a nice formula for the HP embedment depth based on the residual shear value. Thanks for the tip.