Up-hole time domain reflectometry (TDR) devices that interrogate passive mechanical transducers are advantageous for engineering monitoring in situ. This technology is based on transmitting an electromagnetic pulse through a coaxial cable connected to a sensing waveguide and watching for reflections of this transmission due to changes in characteristic impedance along the waveguide. Depending on the design of the waveguide and analysis method, the reflected signal can be used to "sense" various engineering parameters. When embedded in a geotechnical structure, TDR can be seen as a "geonerve" system. New design concepts and data reduction procedures for each type of sensing waveguide are introduced in this article. The versatility and merits of TDR are highlighted by a TDR slope monitoring system example composed of a single TDR device and multiple sensing waveguides.