| Summary: | This thesis presents results of a study of the acoustic emission (AE) monitoring technique for detecting slope deformations. Laboratory studies carried out at Nottingham Trent University to develop and assess an acoustic emission monitoring system, including data processing and interpretation criteria, are described. Due to the low energy of soil generated AE and their high attenuation as they propagate through soil, a key element of the system is the wave guide used to transmit signals from depth within the deforming soil body to the sensor at ground level. This investigation is centred on assessing the performance of 'active' wave guides. A steel tube is located in a pre-drilled borehole with granular surround. Deformation of the host soil results in deformation of the wave guide/backfill system and generation of AE. Interpretation requires information on the location of generated AE along the length of the wave guide and on the relationship between AE and ground deformation rates. Each component of the wave guide system has been investigated to assess its influence on the generated and transmitted signal (i.e. wave guide diameter, connection type, sensor attachment details and backfill soil grading). The main findings from the study are: a) soil generated AE signals can be generated and transmitted by an active wave guide; b) high attenuation and signal dispersion can result from poor connections between wave guide lengths and this reduces the sensitivity of the system; c) AE levels emitted due to bending of the steel wave guide are negligible and need not be considered; d) the source of AE along the wave guide can be located using only one transducer by identifying different velocity signal wave modes (Lamb waves) that travel through thin walled pipes; e) sand backfill soil is responsive to faster deformation rates than gravel and AE amplitude increases with displacement; f) gravel backfill generates detectable AE even under extremely slow rate of deformation (10-4mm1min) and AE increases with displacement but with constant amplitude. This research demonstrates the ability of active wave guides to generate AE in response to very slow ground deformation rates, and hence its potential to provide an early warning of slope instability.
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