Understanding the influence of pore space characteristics on the hydraulic
conductivity and spectral induced polarization (SIP) response is
critical for establishing relationships between the electrical and
hydrological properties of surficial unconsolidated sedimentary deposits,
which host the bulk of the world's readily accessible groundwater
resources. Here, we present the results of laboratory SIP measurements
on industrial-grade, saturated quartz samples with granulometric
characteristics ranging from fine sand to fine gravel, which can
be regarded as proxies for widespread alluvial deposits. We altered
the pore space characteristics by changing (i) the grain size spectra,
(ii) the degree of compaction, and (iii) the level of sorting. We
then examined how these changes affect the SIP response, the hydraulic
conductivity, and the specific surface area of the considered samples.
In general, the results indicate a clear connection between the SIP
response and the granulometric as well as pore space characteristics.
In particular, we observe a systematic correlation between the hydraulic
conductivity and the relaxation time of the Cole-Cole model describing
the observed SIP effect for the entire range of considered grain
sizes. The results do, however, also indicate that the detailed nature
of these relations depends strongly on variations in the pore space
characteristics, such as, for example, the degree of compaction.
The results of this study underline the complexity of the origin
of the SIP signal as well as the difficulty to relate it to a single
structural factor of a studied sample, and hence raise some fundamental
questions with regard to the practical use of SIP measurements as
site- and/or sample-independent predictors of the hydraulic conductivity.