A simple TDR waveform analysis for estimating volumetric water content in marine clays

Abstract

In electrically conductive media such as marine clays, the strong attenuation of electromagnetic (EM) wave energy significantly complicates the determination of travel time, limiting the applicability of traditional time domain reflectometry (TDR) methods for estimating volumetric water content. This study presents an alternative approach that utilizes characteristic voltages in TDR waveforms-specifically, the normalized voltage ratio (V-f/V-0)-to estimate the volumetric water content (theta(v)) and electrical conductivity of marine clays; this approach can be applied even when travel time cannot be determined. Laboratory experiments were conducted on kaolin and bentonite clays with theta(v) between 26.9 and 86.8%, saturated with a 0.5 M NaCl solution. The results show that, for both clay types, V-f/V-0 was highly sensitive to changes in theta(v) and strongly correlated with bulk electrical conductivity, regardless of their mineralogical differences. Empirical relationships were developed to estimate theta(v) for each clay, and a generalized model applicable to tested clays with theta(v) > 50% was proposed, achieving a mean absolute percentage error of 2.5%. This study demonstrates that waveform-based analysis using characteristic voltages can serve as a reliable alternative to traditional travel time-based TDR techniques, thereby expanding the applicability of TDR in highly conductive saline environments such as marine clays.