posted on 2012-11-12, 14:42authored byM.P. Spriggs
Acoustic emission (AE) is a natural phenomenon that occurs when a solid is
subjected to stress. These emissions are produced by all materials during pre
failure. In soil, AE results from the release of energy as particles undergo small
strains. If these emissions can be detected, then it becomes possible to develop an
early warning system to predict slope failure. International research has shown
that AE can be used to detect ground deformations earlier than traditional
techniques, and thus it has a role to play in reducing risk to humans, property and
in mitigating such risks.
This thesis researches the design of a system to quantify the AE and calculate the
distance to the deformation zone, and hence information on the mechanism of
movement.
The quantification of AE is derived from measuring the AE event rate, the output
of which takes the form of a displacement rate. This is accurate to an order of
magnitude, in line with current standards for classifying slope movements The
system also demonstrates great sensitivity to changes within the displacement rate
by an order of magnitude, making the technique suitable to remediation
monitoring.
Knowledge of the position of the shear surface is critical to the planning of cost
effective stabllisation measures. This thesis details the development of a single
sensor source location technique used to obtain the depth of a developing or
existing shear surface within a slope. The active waveguide is used to reduce
attenuation by taking advantage of the relatively low attenuation of metals such as
steel. A method of source location based on the analysis of Lamb wave mode
arrival times at a smgle sensor is summansed. An automatic approach to source
location is demonstrated to locate a regular AE source to within one metre. Overall consideration is also given to field trials and towards the production of
monitoring protocols for data analysis, and the implementation of necessary
emergency/remediation plans.