Geology Reference
In-Depth Information
emplaced and, again, such features need to be interpreted correctly,
both in terms of understanding the geological situation and because
they will affect geotechnical properties.
3.4.13.2 Tension fractures
The
first major work on fracture morphology was by Woodworth
(1896). He observed and illustrated what are now considered classic
expressions of fractures propagating from a
flaw, with typical features
including feather markings and arrest or hackle marks (
Figure 3.49).
Most researchers consider that most such markings involve extension
(tension), although other features probably involve some shear. They
are recognised in all rocks and even drying sediments. They are also
commonly observed in drill core, and distinguishing natural from
induced fractures is an important task for those logging the recovered
rock (Kulander et al., 1990). Such features are signi
cant in their own
right geotechnically but are also important for the interpretation of the
geological history of a site.
Figure 3.49
Shallow bedding
plane with ripple
marks. Near-
vertical surface
with typical arrest
and hackle marks
associated with
tensile fracture
Ling landslide,
Taiwan.
