The Bromhead ring shear apparatus is based on the original
design developed by Bromhead (1979) and is manufactured by
Wykeham-Farrance Engineering Limited. The ring shear specimen
is annular with an inside diameter of 7 cm and an outside
diameter of 10 cm. Drainage is provided by two bronze porous
stones screwed to the bottom of the specimen container and to
the top loading platen.
The specimen is confined radially by the specimen container.
which is 0.5 cm deep. As a result of the confinement. wall friction
is applied to the inner and outer circumferences of the specimen.
The magnitude of wall friction increases with the depth of the
specimen, and thus the plane of least wall friction, or shear
resistance, occurs at or near the soil/top porous stone interface.
This results in the failure plane occurring at or near the knurled
surface of the top porous stone. This type of failure condition is
often referred to as a "smear" condition (Bromhcad 1986).