Investigations of compacted soil-organics mixtures with spectral induced polarization

SUMMARY In this study, we present a new integrated experimental approach to investigate simultaneously the electrical spectral induced polarization (SIP), mechanical, hydraulic and chemical properties of synthetic clayey soil mixed with different types and quantities of organic matter. It addresses knowledge gaps that aim to advance SIP as a non-destructive analysis tool for soils. We used an inorganic clay as a proxy for clayey soil with a moderate cation exchange capacity to achieve more realistic test conditions since most studies use sand. Three organic matter (OM) types with contrasting properties, biosolids, peat and sugar cane residue, broaden the range of organic carbon materials that have been tested. Our study demonstrates a strong relationship between the imaginary part of the complex conductivity and the total organic carbon content of the soil–OM mixtures. It indicates that the relationships depend on the degree of aromaticity, with the slope angle increasing as the degree of aromaticity of the OM increases. Hence, the quantity of OM, as well as its chemical structure, plays a key role in SIP response. Interestingly, these relationships are independent of soil water saturation and bulk density. These findings are of paramount importance for enabling field-scale applications and confirm the potential of SIP as a non-invasive tool for monitoring and characterizing soil in situ.