Seminar - James Schneider - Analysis of soil classification using normalized piezocone parameters

Wednesday 30 July 2008, 1.10 - 1.55 pm
Civil Engineering Lecture Theatre 3

Abstract:

The number of variables which influence cone tip resistance, penetration pore pressures, and CPT sleeve friction typically exceed the range of variables covered by databases of sites used for calibration of correlations for soil classification charts. Therefore, it is important to understand the mechanisms which influence piezocone parameters during the development of design recommendations. Studies have shown that soil strength, and piezocone resistance, are primarily controlled by
(i) initial soil state;
(ii) critical state friction angle;
(iii) degree of consolidation during loading, as well as
(iv) soil stiffness.

To assess these effects on soil classification by piezocone, results of cavity expansion analyses, large strain finite element analyses, variable rate penetration tests in centrifuge clay and silty clay specimens, variable rate penetration tests in natural clay specimens, and a database of field tests sites are compared. This presentation focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter (Bq=Du2/qcnet). The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q-Du2/s'v0 space is superior to Q-Bq space when evaluating piezocone data for a range of soil types. Still, there are zones of overlap for silty soils and heavily overconsolidated clays, thus requiring that information supplementary to Q and Du2/s'v0 be obtained in unfamiliar geologies, including: variable rate penetration tests, dissipation tests, CPT friction ratio, or soil sampling.

About the presenter
James Schneider received his undergraduate and masters degrees from Georgia Tech, Atlanta, USA, in 1997/1999, respectively. The was followed by 4 years of full time geotechnical consulting in the US for Geosyntec Consultants in Atlanta, and Fugro in California. He arrived in Australia in October 2003 to perform a PhD with Civil Engineering / COFS at UWA, supervised by Prof. Barry Lehane. He will starting a teaching position at The University of Wisconsin-Madison on 15 August 2008.