Blow counts for SPT Value 4

[ONENGINEER]

Text books describe SPT testing by penetration readings for three 6" intervals and counting the blow counts for the last 12 inches. i.e. ignoring the reading for the first 6".

Some drillers and software have readings for four 6" penetrations, a total of 24 inches. E.g. blow counts of 12-23-36-40. In the later case what would be the SPT value? 59 or 76 or 61.

 

[fattdad]

haha BigH! Did a job in Panama about 10 years ago (in my pre-DOT days). Dude had a donut hammer, hand auger, tripod and a cathead on a Briggs and Stratton (sp). Dude also had one arm!

He made hole; however. Had a few helpers too!

Life's a bit different outside the USA! That said, when I did work in Seattle (I-95, c. 1979), we had no choice but to drill at that spot! So, we packed in a tripod and did a wash bore. Dude also had a donut for that boring.

Now anybody packed in a Winkie!

f-d

ípapß gordo ainÆt no madre flaca!

 

[aeoliantexan]

Since the post is already hijacked, let me join the club. I had a summer job with Corps of Engineers, Alaska District, many years ago. Helped a Corps geologist drill test borings in a bay southeast of Juneau using a tripod, gas-driven cathead, 2" pump, A-rods, 3" casing. and pipe wrenches. We set up on a 12' by 16' raft and drilled in the bay for a dock, dealing with 15-foot tides every day. The only hammer we could get was a 300-pound casing hammer. The geologist could pick it up!

Heck of an adventure for an Iowa farm boy!

 

[oldestguy]

Here goes OG with a photo from US Bureau of Reclamation manual 1963. Hand auger borings to 55 feet. guide ring set at 30 feet in borrow area, 4" diam samples.

 

[geomane]

OG, is that you in that photo?

 

[Ron]

Nice tripod! Ours wasn't that cool! Had to use forked branches of a large oak tree to stack rod on one job! Ours was more like what f-d described....cathead on a Briggs and Stratton with donut hammer.

 

[pelelo]

In my area, drillers take 24-in samples for environmental purposes.

SPT-N values are computed as usual: the sum of the 2nd and 3rd blowcounts.

 

[mikeofBelAir]

Having drilled and run a few hundred SPT, and observed hundreds more, I think the best advance in SPT is the nearly universal use of the automatic hammers. Anybody else watch a driller with 3 wraps on the cathead, and already pulling up before the hammer hits? How consistent was the energy applied to the drill string? How useful were the blow counts? Drillers got paid for FOOTAGE; --the sampling and SPT were a nuisance. The only SPT blow counts done with a cathead that I ever trusted were those I did myself.