Dear Wilf,
Not at all surprising and very common in heavily overconsoliadted clays with
filter in shoulder position. We have many examples in the UK. I see Paul M
beat me to a response and his list of references are a good source. If you'd
like to discuss and compare UK data then get back to me.
John
John J M Powell
Centre for Ground Engineering
BRE
PS an example for Gault clay appears in - Lunne, T, Robertson, P.K . and
Powell, J.J.M. (1997):"CPT in geotechnical practice". Spon Press, London.
-----Original Message-----
From: Wilfred Wrigley [mailto:[log in to unmask]]
Sent: 20 April 2001 21:12
To: [log in to unmask]
Subject: CPTU Dissipation Tests
I have carried out electronic piezocone pore pressure dissipation tests on
several sites in the UK. I have observed that during some tests, usually in
overconsolidated clays, there is an initial period of pore pressure build up
which can last anywhere from a few seconds to 200 minutes, followed by a
dissipation phase.
Has anyone else observed this type of response and does anyone have an
explanation? I have noticed that where a number of tests has been carried
out in one profile some of the the tests do not show the initial pressure
build up phase and hence the response is unlikely to be due to desaturation
of the porous element or system felxibility. I have not seen any
publications describing the phenomenon or any published analyses to explain
it.
I would be greatful for any comments or references.
Wilf
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