Geology Reference
In-Depth Information
Figure 3.46
Sheeting joints in
granite, Mount
Bukansan, near
Climbers show the
scale.
movements within the weak mass rather than by initiating a new
tensile fracture (Vidal Romani & Twidale, 1999). Therefore, where
sheeting joints are found in highly fractured rock masses, it is likely
that they predate the gradual development of the other joints, as
mechanical fractures during unloading and weathering (Hencher,
2006; Hencher & Knipe, 2007).
Figure 3.47
shows the stereographic
representation of sheeting joints at a site in Hong Kong, together with
cross joints, perpendicular to the sheeting joints and at right angles to
the azimuth of dip, which indicates their likely tensile origin.
The shape of discontinuity surfaces is important to rock engineering,
not least because of its in
uence on shear strength, and this is dealt
Figure 3.47
Stereonet showing
sheeting joints and
cross joints at 90
degrees. Tuen Mun
Highway, Hong
Kong (after
Hencher et al.,
2011).
North
Sheeting
joints
East
West
Cross joints
Note lack of
any set
orthogonal to
cross joints
Sheeting joints
South
Direction of dip of
sheeting joints
