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Dilatancy characterization of sands using the resistivity cone penetration test Kokan, Matthew J.


The determination of in situ dilatancy in sands has been a difficult and elusive objective in site investigations. Difficulty with sampling, as well as problems with extrapolating laboratory results to field performance have caused geotechnical engineers to place increased reliance on in situ tests. One such test which is gaining acceptance in the geotechnical profession is the cone penetration test (CPT). As with other in situ tests, the CPT can be used to predict dilatancy behaviour of sands based on empirical correlations. As with most empirical methods, correlations are often site specific and sensitive to variables that are not readily measurable. A new, geophysically based, technique has been developed to determine dilatancy characteristics of sands in situ. The resistivity cone penetration test (RCPT) employs a standard 10 sq cm piezo cone, paired with a module which measures soil resisitivity at different electrode spacings. The resistivity is recorded in a semi—continuous manner along with regular CPT data. The resistivity measurements at different electrode spacings can be used to infer sand densities at different distances from the penetrating probe. By comparing the resistivity close to the probe with the resistivity further away from the probe, it is possible to observe the shear induced volume change caused by penetration of the probe. This approach is analytical and does not require water sampling, nor is it site specific. Data are presented to illustrate the effectiveness of this technique in determining in situ dilatancy of sands. The technique is compared to existing empirically based approaches for prediction of dilatancy. Finally, possible future applications of the RCPT are discussed.

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