Time Domain Reflectometry Development for Use in Geotechnical Engineering

TLDR

Time domain reflectometry, originally used to locate faults in transmission lines, is being extended to geotechnical engineering. The study develops TDR probes, installation and testing methods, and new dielectric‑constant–to‑water‑content relationships for soil. Coaxial and modified multiple‑rod probes were built, and analytical solutions were derived to quantify sampling volume, spatial bias, soil disturbance, and air‑gap effects during in‑situ dielectric measurements. Experimental validation confirmed the solutions, new calibration equations improved water‑content estimation, and the probes and methods were shown to be applicable for measuring soil water content and density.

Abstract

Abstract This study extends the use of time domain reflectometry (TDR) in geotechnical engineering, a technique originally developed to locate faults in transmission lines. Different elements of the TDR technique are developed, including design of TDR probes, probe installation/test methodology, and relationships between TDR measured dielectric constant and water content of soil. A coaxial probe is developed that is used for measuring the dielectric constant of soil prepared in a cylindrical cell or compaction mold. A multiple-rod field probe is developed that modifies previously developed multiple-rod probes and extends their capability for measuring the in-place dielectric constant of soil. An analytical solution is developed to determine the sampling volume and spatial bias of the TDR measurement. The solution is extended to study the effect of soil disturbance and presence of air gaps due to probe insertion. Experimental results validate the solutions. New relationships are proposed between dielectric constant and water content to eliminate some of the limitations of the existing calibration relationships. Several possible applications of the developed probes, test methodology, and calibration equations for measuring water content and density of soil are illustrated.