A New Geotechnical Ring-Shear Device for the Investigation of Fault Zone Permeability: Design and Preliminary Results

M. Ben Clennell, Rob J. Knipe, and Alex J. Maltman

The ring-shear permeameter designed by Kevin M. Brown and others at the University of Birmingham demonstrated the feasibility of torsional shear methods for the investigation of the hydrogeological properties of fault zones. The new permeameter described here is based on the much larger Imperial College ring-shear device. While it operates at lower effective stresses (2 as opposed to 20 megapascals), the Leeds device has a larger sample chamber that enables sandy, as well as fine-grained sediments, to be tested. The sealed chamber is split into upper and lower halves, which rotate relative to one another, so that the sample fails along a horizontal mid-plane. This feature enables accurate shear strength determinations to be made, and also allows the measurement, or control, of mid-plane pore fluid pressure during tests. Preliminary results of peak strength, residual shear strength, volumetric history, pore-pressure and permeability evolution are reported for clays, sand-clay mixtures and remoulded samples of silty clay from Ocean Drilling Program Leg 146 (Cascadia accretionary wedge)

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California