Quantification of slope displacement rates using acoustic emission monitoring

In soil slopes, developing shear surfaces generate acoustic emission (AE). The Authors have previously proposed the use of active waveguides for monitoring the stability of such slopes. Active waveguides comprise of a steel tube installed in a preformed borehole through a slope with coarse grained soil backfill placed in the annulus around the tube. Deformation of the host soil generates AE in the active waveguide. Field trials of this system reported previously have shown that AE rates are linked to slope deformation rates. This paper extends the study by detailing a method for quantifying slope movement rates using an active waveguide. A series of laboratory experiments are presented and used to define the relationship between AE event count rate and displacement rate. The method was shown to differentiate rates within an order of magnitude, which is consistent with standard landslide movement classification (i.e. 1 to 0.001 mm per minute), using a relationship derived between the gradient of the event count rate with time and deformation rate. In addition, it was possible to detect a change in displacement rate within two minutes of it occurring even at very slow rates (i.e. 0.0018mm/min). Knowledge of changes in displacement rate is important in situations where slope movements are suddenly triggered or displacements accelerate in response to a destabilising event. Field trials of a realtime AE monitoring system are currently in progress to compare performance against traditional instrumentation.