Electromagnetic wave propagation model for differentiation of geotechnical disturbances along buried cables

The lumped-circuit, hybrid, finite-difference/FFT (fast Fourier transform) model described herein simulates effects of multiple discontinuities in a coaxial cable at variable distances on a time domain reflectometry (TDR) signature. This model is verified by comparison with measured reflections from perfectly defined, multiple deformities. Accurate simulation is an important component of TDR technology as it allows improved calculation of the amount of shearing at multiple locations along special cables grouted in a rock or soil mass. This paper is arranged in four sections. The introduction or background section presents the need for the model, nature of discontinuities, and the uses of long TDR cables. Design of the hybrid computer model is presented in the following section: Modeling of Coaxial Cable Response. Calculated and field-measured signatures are compared and methods of calibration are introduced in the section entitled: Calibration of Model and Comparison with Field Data. The paper closes with a summary and conclusions.