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Geological Society, London, Special Publications; 2007; v. 270; p. 93-99;
DOI: 10.1144/GSL.SP.2007.270.01.07
© 2007 Geological Society of London

Geophysics

Laboratory measurements of acoustic emissions and wave velocities associated with the formation of fractures in sandstones

W. S. Pettitt1 & M. S. King2

1 Applied Seismology Consultants Ltd, 5 Swan Hill Court, Shrewsbury SY1 1NP, UK (e-mail: will{at}seismology.org)
2 Department of Earth Science & Engineering, Imperial College London, London SW7 2AZ, UK (e-mail: m.s.king{at}imperial.ac.uk)

Acoustic emission (AE), ultrasonic velocity and petrophysical property measurements are increasingly being used as tools to investigate mechanical, thermal and hydraulic changes in rock masses around underground excavations and in the exploration of oil and gas. In order to develop these measurements into an effective tool it is necessary to understand how they relate to changes in the fracture and fluid content under controlled laboratory conditions. A polyaxial (true triaxial) test system has been developed to perform high-resolution measurements of AE, ultrasonic velocities and fluid permeability characteristics in a cubic specimen under true-triaxial stress. The polyaxial system also allows the measurement of AEs using an array of small-diameter, high-frequency transducers. The measurements allow the AE source locations and mechanisms to be calculated, thus providing an analysis of the distribution, orientation and type of fracture growth in the specimens. Example results are given from an experiment, showing that AE mechanisms during crack initiation describe a dominant failure mode with a significant tensile component.