iGEM Book Review
GeoMeasurements by Pulsing Cables and Probes
by O'Connor, K.M. & Dowding, C.H. (1999)
CRC Press, 424 pp, $ 69.95,
This book examines Time Domain Reflectometry research and provides practical information on its use in geomaterials. Time Domain Reflectometry (TDR) is an electromagnetic technique originally developed to detect faults along power transmission lines. It is an emerging technology in the field of geotechnical instrumentation. A cable tester, connected at one end of a cable, sends a step voltage pulse along the line and records the travel time of any voltage reflections resulting from cable discontinuities. Knowing the pulse propagation velocity, the time records can be converted to distance measurements. In addition, the reflection amplitude can be directly related to the magnitude of cable deformation.
In geotechnical engineering, TDR technology has proven effective and is currently used in a number of projects to measure rock mass deformation along joint interfaces and soil shear zones. Other existing geotechnical uses of TDR include measuring soil moisture and ground water level monitoring.
The authors’ stated intent was to crystallize the commonalities among the seemingly divergent specialties employing TDR technology in geomaterials. To achieve this goal, discussion of principles is separated from that of case histories of application for soil moisture and rock and soil deformation throughout the book. Each chapter focuses on separate areas of application and starts with a short introductory paragraph and outline of topics follows to more fully describe the contents.
Chapter 2 describes the basic physics of signal generation, transmission, attenuation, and reflection along the coaxial cable. Chapter 3 discusses monitoring of soil moisture in unsaturated geomaterials, probe design and procedures for their calibration as well as the variation in probe responses to changes in water content and soil mineralogy. The validity of TDR to measure water content of soils must be assessed by comparison with other techniques commonly used. Chapter 4 presents such comparative studies with lysimeters, Bowen ratio, neutron probes, and nuclear density gauges.
Monitoring deformation with TDR developed from the original purpose of this technology, namely, identification of cable faults or deformations along telephone and power cables. The next four chapters are devoted to TDR deformation monitoring. Chapter 5 presents variations in waveform characteristics associated with cable deformation, cable calibration, and installation techniques for metallic cables in rock. Field experience and verification of rock measurement form the focus of Chapter 6 which includes a number of case histories that illustrate the variety of environments wherein TDR rock deformation monitoring has been successfully employed. In addition to developing the rationale for the use of compliant TDR cable/grout system to monitor soil deformation, Chapter 7 presents several cases that demonstrate use of TDR cables in soil as well as weathered and soft rock. Chapter 8 discusses the use of both metallic cable and optical fiber to monitor internal and external deformation response of structures.
Chapter 9 develops the background necessary for TDR measurement of fluid levels and discrimination of fluid types. TDR methods are compared with other approaches to measure pore water pressure near critical structures such as dams, as well as changes in ground water table elevation. The two final chapters discuss electronics, including sensor/transducer components and connections from the sensors to the TDR pulser/sampler, and system control methods (Chapter 10), and available software for transmission and analysis of TDR signatures (Chapter 11).
Rapidly changing and most useful information is included in appendices such as contact information for vendors, as well as cable and grout properties. Exhaustive references, lists of symbols, author index and subject index are also attached at the end of the book. The book is clearly written and the text, figures, and tables are produced to a high quality.
Geo Measurements by Pulsing TDR Cables and Probes deftly and elegantly brings together timely and in-depth information on an emerging technology for monitoring of geo-structures. The book is written by authors with long standing research and consulting experience in TDR geo-monitoring design and installation. It discusses in great detail not only “how to do it” but also “how it was done” based on a variety of case histories many of them comparing TDR technology with other commonly used instruments. A plus of the book is that it is supported extensively on the Internet through a TDR clearinghouse, an annotated bibliography, and several list servers maintained by the authors.
Because of the broad spectrum of measurement possible with TDR, this book is of interest to a wide variety of scientists, engineers, and contractors in geotechnical, environmental, mining and agricultural engineering. It represents a significant contribution to the challenging field of geo-monitoring and should be recommended as a reference for university libraries, research corporations, and engineering consulting firms.
Professor Mihail Popescu
Illinois Institute of Technology
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