The mean joint spacings for all joint classes and
all weathering grades are shown in Table 3; standard
deviations give a sense of the range and shape of the
distribution. Vertical joint spacing in fresh granite is
wider by one-third than in weathered granite; horizontal
and dipping joint spacings are also wider but
by at least 100%. The large decreases in mean
horizontal and vertical joint spacing between fresh
and SW granite were unexpected because the main
difference between these two weathering grades is
the limited staining that occurs along the joints and
joint faces in SW granite; staining is absent in fresh granite. This may result from poor lighting in the
tunnels where fresh granite occurred; smaller joint
spacings may have been overlooked. The very close
joint spacing in MW granite was expected because
this grade represents the stage at which microcracks
begin to open, and decomposition has spread
throughout the rock material. The wide spacing in
CW granite could result from crystal disaggregation.
As the rock weathers and progressively disintegrates,
individual crystals expand to fill all available space,
including joints. As noted above, the distinctive linear
pattern of the joint traces is replaced by discontinuous
curvilinear line segments. It is likely that
relict joints are present.
The means for dipping and horizontal joint spacings
in fresh granite and weathered granite are statistically
significantly different; this comparison is
across weathering grades. Vertical joint spacing
means in fresh granite are significantly different
form those in weathered granite except for CW
granite. There are no significant differences among
the medians for the three joint types. The medians
are shown in Table 4.