The purpose of this paper is to describe two out of several unconventional instrumentation schemes which are useful for detecting the onset and monitoring the progression of slope instabilities. The devices concerned are the strip gauge and the long span displacement gauge and both were originally conceived for use in nuclear weapons testing programmes, to measure the gross dynamic soil and rock motions associated with such tests.
Both gauges are equally suitable for measuring the quasi-static creep motion of slopes which characteristically precede soil and rock slides, the initial parts of the actual slide motion itself and, if subsequently arrested, the time history of slope settlement and stabilisation.
Both gauges can be made to substantial lengths so that it becomes feasible to monitor the displacement trends of any medium along a line of expected motion in three mutually orthogonal axes. By arranging the gauges in a matrix, the motion of a large surface or plane can be monitored and, although not yet attempted, it is now possible to monitor the strains and motions of large volumes of suspect soil and rock. By comparison it would be prohibitively expensive to attempt the same measurement with individual, or discrete transducers.
The strip gauge was first used to measure the horizontal displacement occurring at various depths in a soil mass due to a large magnitude surface detonation. The blast effect produced a crater and several unexpected subterranean motions during its formation. These were recorded via the strain gauges on the strip