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.Applied Science, Faculty ofCivil Engineering, Department ofGraduat
