Comments on: Geologists at work http://oaklandgeology.wordpress.com/2009/08/31/geologists-at-work/ focused on, near and under Oakland, California Wed, 22 May 2013 03:36:30 +0000 hourly 1 http://wordpress.com/ By: Andrew http://oaklandgeology.wordpress.com/2009/08/31/geologists-at-work/#comment-914 Tue, 01 Sep 2009 16:23:57 +0000 http://oaklandgeology.wordpress.com/?p=542#comment-914 Thanks, Erik. That makes more sense than measuring raw power, which would always rise with depth. My linked page makes that clear (should have read it before writing this!).

]]> By: Erik http://oaklandgeology.wordpress.com/2009/08/31/geologists-at-work/#comment-913 Tue, 01 Sep 2009 14:16:54 +0000 http://oaklandgeology.wordpress.com/?p=542#comment-913 Actually they usually don’t measure power, but pressure on the cone tip and drag on a friction sleeve behind the cone tip as it penetrates, in addition to those other things. The ratio ratio of tip pressure and sleeve friction can tell you soil type, less than 1% is probably sand, 3-10% or greater is probably clayey.

They can also can have a geophone at the tip so you can do down-hole seismic velocity tests during penetration.

CPT gives a continuous profile (usually every couple of cm) of all the things it is measuring so it can be very good for finding thin soil layers that even a very careful driller might miss in a boring. It’s also very fast; you can easily push over 500 ft/day if you don’t have to stop for seismic testing. You do have to be careful in gravelly soils because the results can be very misleading, and if there is too much gravel or anything coarser then you can actually damage the cone tip.

]]> By: Naomi Schiff http://oaklandgeology.wordpress.com/2009/08/31/geologists-at-work/#comment-912 Tue, 01 Sep 2009 05:48:39 +0000 http://oaklandgeology.wordpress.com/?p=542#comment-912 Anyone who uses the word “ovipositor” in a nonbiological simile gets my vote to go anywhere he wants!

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