Motivation: In Civil and Geotechnical engineering, dry density of soil and water content of soil are two important parameters used for construction control

They are usually measured using a radiation source with a known particle emission rate and a sensor placed to intercept particles traveling through the soil. Although 90% of the US market uses this technology, it is costly and hazardous.

An alternate approach is to measure electrical properties (dielectric constant, conductivity, etc.) using Time Domain Reflectometry (TDR). The soil parameters of interest are then calculated from the electrical parameters.

TDR Measurement System

Time Domain Reflectometry for Soil Property Estimation and Construction ControlMembers: Qi Yang, Huayi Guo, Nathan van Eyk, Stephen Kaufman; Graduate mentors: Joon Young Kim, Alex Layton, Andrew Balmos; Prof. V.P. Drnevich, Prof. J. V. Krogmeier

What We Are Working On:

1. Establishing wireless connections between existing TDR device, which now use Ethernet cable or RS 232 serial cable, and also selecting and purchasing new hardware. – Subteam of Nathan and Stephen

2. Continuing Programming of algorithms in MATLAB to implement new theory, and converting them to Java for use in Android devices. – Subteam of Tom and Huayi

Future Goals: • Incorporate GPS to record field test

locations• Integrate Bluetooth or WI-FI technology

to transmit data wirelessly• Test the system in the field• Implement a soil temperature sensor into

the probe design

TDR Curve Measurements

Typical Voltage Trace for Clayey Soils

Values directly measured from the curve:• Vo: Initial reference voltage (red region)• Vin: Voltage in the 50 ohm coaxial cable (blue region)• V1: Potential difference between first reflection point and the

second reflection point• La: Distance wave propagates between two reflection points• V2: Potential difference between the inflection point after

maximum curvature and the trough voltage point.• Vf: Asymptotic value of the rising exponential fit to the end of

the curve (Final DC voltage)

Electrical parameters derived:• Ka: apparent dielectric constant of soil• ECb: DC electrical conductivity of the soil

Transmission Line Soil Measurement Concept