Complex conductivity porosimetry during unconfined soil compression

Abstract

The unconfined compressive strength (UCS) test is one of the most utilized geotechnical soil analysis techniques for soil stability evaluation. Understanding soil pore size changes during a UCS test is important for estimating soil saturation changes and can help in real-time estimation of soil mechanical state (from liquid to a plastic, to a semisolid, and to a solid state). Here, we performed a UCS test on a synthetic soil mixture of silica sand (98%) and fine kaolin powder (2%) which was saturated below its liquid limit (Sw = 68%). Concurrently, we measured complex conductivity signals of the soil associated with pore size distribution changes resulting from compression. Our results show that soil deformation and failure during a UCS test have measurable impacts on complex conductivity signals of the soil. The pore size distribution of the soil was estimated from a Debye decomposition inversion performed on the measured complex conductivity spectra. On average, an order of magnitude reduction in the dominant pore size of the soil was estimated from complex conductivity measurements. Our findings show that complex conductivity measurements might be used in conjunction with geotechnical measurements for estimating soil porosity and pore size distribution changes.