Abstract
In situations where important structures are located over subsurface cavities, decision makers need a quantitative measure of the likelihood of subsidence occurring. A state-of-the-art sensor has been developed based on the principle of time domain reflectometry (TDR). It has been used to monitor stability of crown pillars over abandoned gold mines in Nova Scotia and Ontario as well as strata movements over abandoned coal mines in Illinois and Ohio. Coaxial cables are grouted into a rock mass which is expected to cave. Rock movement deforms the cable and produces changes in TDR pulse reflection signatures. This technology has been advanced such that it is possible to not only locate but also characterize and quantify rock mass displacements by analyzing changes in these signatures. The remote monitoring capability available with TDR provides many benefits including: 1) the ability to interrogate cables as frequently as desired which has minimized data loss prior to cable “failure”, and 2) data is acquired in digital form so it can be analyzed in real time. An example case is presented in which automated TDR monitoring was an integral part of the site selection process for a new school building.
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