Correlation of vibracore rate of advance data with N blow counts
Correlation of vibracore rate of advance data with N blow counts
(OP)
I'm a geologist and an environmental engineer but not a geotech. I'm working a project where we're faced with enough cobble and trash to make a geoprobe unworkable, and enough running sands to frustrate a standard split spoon sampling drill rig. I'm after good samples and recovery but a geotech is going to need enough information to design sheetpile bulkheads along a river channel. Has enough research been done yet to be able to use the results of a vibracore rig to generate the standard blow count information a geotech would need for foundation engineering? Is there a publication out there more recent than an old early "80' ASCE document that addresses this?





RE: Correlation of vibracore rate of advance data with N blow counts
RE: Correlation of vibracore rate of advance data with N blow counts
The question to the community is whether there has been enough data developed on sonic (or vibracore) sampling so that geotechs can derive the design data they need from either the vibracore information, by slicing the recovered core and using field tools, or by sending in sections of the core to a lab to generate the design data needed.
RE: Correlation of vibracore rate of advance data with N blow counts
Are the cobbles too large for hollow-stemmed augers to get by? Can the driller use smaller augers, or rotary with casing, to get through the cobble zone? The geotech will probably want both "N" values and samples for grain size distrbution data.
Some of the more knowledgeable forum members like Focht3, SirAl, et al, may have info regarding the coorelation you seek. Wait to see if they post.
Good Luck.
RE: Correlation of vibracore rate of advance data with N blow counts
RE: Correlation of vibracore rate of advance data with N blow counts
You have a tough problem - but you need to understand a fundamental concept: good environmental boring equipment - and drilling techniques - make absolutely horrible geotechnical borings. Don't try to make your borings "dual use" - you're wasting the owner's money. Been there, done that.
I don't have any confidence in vibracore readings for this application - debris and cobbles are too variable. The correlation is tenuous at best, and you don't have a particularly "uniform" site -
The cobbles may be hell to get through regardless of the (conventional) equipment used. I spent three or four very long nights on the shoulder of SR 91 aka the Riverside Freeway east of L.A. trying to drill through a layer of cobbles near the maximum scour depth of the Santa Ana River. Got HSA stuck (Mobile 67) at about 95 feet; same thing for a CME 95 using wash rotary. We lost circulation for good at about that depth, too.
How deep do you think the cobbles and trash are? Proportion of each? Are the cobbles natural, or placed by man? You may have to remove some of it and replace it with clean sand in order to drill the borings.
Finally, sheet piles may not be practical for this site...
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.
RE: Correlation of vibracore rate of advance data with N blow counts
RE: Correlation of vibracore rate of advance data with N blow counts
RE: Correlation of vibracore rate of advance data with N blow counts
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.
RE: Correlation of vibracore rate of advance data with N blow counts
Sy and Campanella (1984) "Becker and Std Penetration Tests (BPT-SPT) Correlations with Consideration of Casing Friction," Can Geo Jour Vol 31, No. 3, pp 343 to 356.
Harder and Seed (1986) "determination of penetration resistance for coarse=grained soils using the Becker hammer drill," Report UCB/EERC-86/06, Earthquake Engineering Research Centre, University of California, Berkely, 126pp.