Time domain reflectometry development for use in geotechnical engineering

This study extends the use of time domain reflectometry (TDR) in geotechnic al engineering, a technique originally developed to locate faults in transm ission lines. Different elements of the TDR technique are developed, includ ing design of TDR probes, probe installation/test methodology, and relation ships between TDR measured dielectric constant and water content of soil. A coaxial probe is developed that is used for measuring the dielectric const ant of soil prepared in a cylindrical cell or compaction mold. A multiple-r od 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 samp ling volume and spatial bias of the TDR measurement. The solution is extend ed to study the effect of soil disturbance and presence of air gaps due to probe insertion. Experimental results validate the solutions. New relations hips are proposed between dielectric constant and water content to eliminat e some of the limitations of the existing calibration relationships. Severa l possible applications of the developed probes, test methodology, and cali bration equations for measuring water content and density of soil are illus trated.