Development of a Time Domain Reflectometry System to Monitor Landslide Activity: Final Report -- FHWA/CA/TL-96/09 June 1996

by
William F. Kane, Principal Investigator
wkane@compuserve.com
Hernan Perez
Neil O. Anderson
Department of Civil Engineering
University of the Pacific
Stockton, CA 95211

Prepared for
Timothy J. Beck, Project Manager
California Department of Transportation
Office of Structural Foundations
5900 Folsom Boulevard
P.O. Box 19128
Sacramento, CA 95819-0128

Table of Contents

EXECUTIVE SUMMARY

This report describes the results of a research project to investigate the use of time domain reflectometry (TDR) to monitor landslide movement. The use of coaxial cables and TDR to monitor earth movements is relatively new. The method uses the changes in the signature of a voltage pulse traveling along a coaxial cable grouted into a borehole. In this research, three coaxial cables (RG59/U) were grouted into boreholes in the Grapevine landslide, Kern County, California adjacent to Interstate Highway 5.

The following tasks were accomplished:

  1. TDR literature review and compilation of an extensive bibliography on the application of TDR in geotechnical engineering
  2. Procurement of computer, cable testers, and other equipment for remote data acquisition of TDR data
  3. Installation and verification of software programs and methodology to read TDR cables installed in landslides
  4. Installation of remote data acquisition equipment at the Grapevine Landslide including electronic hook-up and mobile phone connection
  5. Collection of TDR data by use of notebook computer
  6. Laboratory testing of RG59/U cable to determine tensile behavior and corresponding TDR signatures
  7. Writing data acquisition program and installing in datalogger
  8. Analysis of TDR data from Grapevine Landslide

TDR provides Caltrans with an alternative method to inclinometers in monitoring unstable slopes. It is an economical means of monitoring landslide movement that is safe and easy to use.

ACKNOWLEDGMENTS

The authors would like to thank several of the early investigators who used time domain reflectometry for geomechanics. Dr. Kevin O'Connor of GeoTDR, Minneapolis, Minnesota, and formerly of the U.S. Bureau of Mines Twin Cities Research Center, was a strong supporter of this project. Dr. O'Connor and the Bureau loaned the equipment and supplied much early technical support and training.

Dr. Cathy Aimone of New Mexico Technical Institute was invaluable in sharing information on cable properties and behavior. In addition, Dr. Aimone arranged a tour of the Waste Isolation Pilot Plant in Carlsbad, New Mexico, which allowed a first-hand glimpse of some important time domain reflectometry work.

Dr. Timothy Asten of the Canada Centre for Mineral and Energy Technology was extremely helpful in sharing information and techniques on his own slope stability and ground movement projects.

Special thanks are due to University of the Pacific students Elizabeth Freeman, Misti Gwinnup-Green, Larry Huang, and Jeremy White for careful proofreading and excellent suggestions.

Without these individuals, the successes and findings of this project would be greatly diminished. Any errors or omissions are strictly the responsibility of the authors.

LIST OF SYMBOLS AND ABBREVIATIONS

Caltrans California Department of Transportation
CANMET Canada Centre for Mineral and Energy Technology
ft feet
in inches
km kilometers
lbs pounds force
m meters
mi miles
mm millimeters
mp millirhos
N (kN) Pa (kPA)
TDR time domain reflectometry
USBM United States Bureau of Mines
Vp velocity of propagation
WIPP Waste Isolation Pilot Project

SI CONVERSIONS

Length Area Volume Mass/Weight Pressure
1 in = 25.4 mm 1 in2 = 645 mm2 1 ft3 = 0.03 m3 1 lbm = 0.5 kg 1 psi = 6.9 kPa
1 ft = 0.3 m 1 ft2 = 0.09 m2 1 yd3 = 20.6 m3 1 short ton = 907 kg 1 psf = 48 Pa
1 yd = 0.9m 1 mi2 = 2.6 km2 1 lbf = 4.5 N
1 mi = 2.6 km 1 acre = 0.4 ha 1 lb/ft3 = 0.15 kN/m3

Last modified 07-09-97

| Table of Contents | Executive Summary | Chapter 1. Introduction | Chapter 2. Laboratory Testing |
| Chapter 3. Installation and Results | Chapter 4. Discussion | Appendices | List of Figures and Tables