WATER CONTENT AND DENSITY OF SOIL INSITU BY THE PURDUE TDR METHOD

The Purdue TDR Method for water content and density, developed by Siddiqui and Drnevich in 1995, is a story of two “coaxial cables" of soil. Driving four metal “spikes” into the soil surface in a pattern that simulates a cable creates one of the “coaxial cables." The second “coaxial cable” consists of a metal compaction mold filled with soil and a metal rod driven into the center of the soil-filled mold for the center lead. The same probe head measures the “apparent dielectric constant” in both the field and mold. With the total density of the measured in the compaction mold, the gravimetric water content is calculated for the soil using the Siddiqui-Drnevich equation which accounts for soil type and density. Water contents determined by this method compare exceptionally well with those obtained by oven drying. If the soil in the compaction mold is the same soil and has the same water content as tested in the insitu “cable”, then the density of the soil insitu is determined from the Siddiqui-Drnevich Equation.

This paper will describe the above procedure in detail and will focus on newly developed algorithms for accurate wave reflection determination that are important for accurate "apparent length", water content, and insitu density determinations.

Vincent P. Drnevich
Professor, School of Civil Engineering
Purdue University
West Lafayette, Indiana

Safiqul Siddiqui
Project Engineer, Earth Exploration, Inc.,,
Indianapolis, Indiana

Janet Lovell
Laboratory Manager, School of Civil Engineering
Purdue University
West Lafayette, Indiana

Quanghee Yi
Graduate Research Assistant, School of Civil Engineering
Purdue University
West Lafayette, Indiana