Acoustic emission source studies of microcracking in rock.
Acoustic emissions (AEs) are generated as a result of the creation of, or movement on
microcracks in a rock mass. Hypocentres of AEs have been used as a very effective method
of visualising the extent (amount and location) of microcrack damage. Studies have used
AE locations to investigate both the behaviour of rock failure in laboratory experiments,
and to evaluate damage in the Excavation Disturbed Zone (EDZ) around underground
openings. The latter has particular significance for the safe storage of nuclear materials in
deep underground facilities.
Because AEs represent phenomena associated directly with the physical processes
occurring in microcracking, then they can also be used to evaluate the fundamental
mechanics of the failure. In this thesis a moment tensor (MT) inversion procedure is
developed for AEs. This utilises full-waveform records from an array of ultrasonic
piezoelectric transducers distributed around the rock mass. The procedure is tested using
synthetic amplitudes and is shown to be robust even with high amplitude uncertainties. The
inversion is particularly good at resolving the volumetric component in the source. The
procedure allows a precise and well-constrained analysis of the forces that are creating the
AEs, and, in some cases, that are actually creating the damage. The mechanics can then be
related to the stress field in the rock mass, or can be compared to results from dynamic
Three case studies are performed. Two of these investigate the fundamental
behaviour of microcracking in the laboratory. A series of laboratory tests are conducted
using polyaxial stress to study the mechanics of damage under realistic in situ stress paths.
The third case study investigates the mechanics of failure operating in the EDZ. AEs are
shown to be truly scaled earthquakes although with often-complex non-double-couple