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The determination of in situ properties of sand has proven to be a difficult objective, especially when it includes assessing volume change characteristics like dilatancy. Difficulty in obtaining representative undisturbed specimens as well as problems with extrapolating laboratory test results to the field has caused many to place increased reliance on in situ testing. One such test that is continuing to gain acceptance is the piezocone penetration test (CPTU). While the CPTU is particularly good for stratigraphic detailing and evaluating many geotechnical parameters, the assessment of volume change characteristics is, as yet, not well defined.
A new approach has been developed which uses the measurement of bulk soil resistivity, a geophysical technique, to evaluate in situ dilatancy characteristics of sand. The method makes use of a module mounted behind a standard piezocone to measure resistivity. The interpretation is based on the resistivity contrast between remolded sand at constant volume conditions and relatively undisturbed sand. These measurements are recorded continually along with the usual CPTU data and are therefore logging the dilatancy characteristics at high-depth resolution. A discussion of the method of analysis, assumptions, and limitations is given, and typical results are presented and compared. To date the results suggest that the method developed does not require groundwater sampling or laboratory testing, an obvious advantage. Thus, a dilatancy parameter is measured in combination with the CPTU identified soil stratigraphy and geotechnical properties, and all data are obtained at the same speed and reliability.
Professor, The University of British Columbia, Vancouver, BC
Staff engineer, Conetec Investigations, Ltd., Vancouver, BC
Stock #: GTJ10288J