Acoustic emission monitoring of slope instability: development of an active waveguide system

This paper introduces the concept of using active waveguides as part of an acoustic emission monitoring system for assessing the stability of soil slopes. In soil, acoustic emissions are generated by inter-particle friction, and hence the detection of acoustic emission is an indication of straining. The components of a field monitoring system are introduced, and the factors controlling design and performance of waveguides are discussed. It is proposed that active waveguides (i.e. those that generate acoustic emission when deformed by the host soil) can be used as an efficient method of obtaining signals from depth within a deforming soil body. The results of laboratory tests conducted to validate the active waveguide model are presented. The role played by the soil surrounding the steel tube waveguide is highlighted. Results from two full-scale field trials that involved monitoring unstable slopes provide evidence for the relationship between detected acoustic emission and slope deformation rate. It is shown that active waveguides in conjunction with relevant signal processing methods can be used to provide an early indication of slope instability.