4. Results
The types of rock mass structures controlling the stability of slopes
include primary rock fabric (e.g. sedimentary stratification and
metamorphic foliation), and secondary tectonic and weathering structures
(Stead and Wolter, 2015). The dominant structural type in the diorite
and granite rock mass in the WL region is tectonic (Townend et al.,
2004). Overall a total of 2322 structures were measured including 537,
510, 560, 417 and 298 structures at sites 1 to 5 respectively (Fig. 4).
Based on the results, 5 predominant joint sets were identified in the
study area. Joint sets J1 and J2, whose dips are greater than 56°, are
conjugate joint sets created probably due to tectonism under a condition
of vertical maximum principal stress. The two joint sets are most
commonly and clearly exposed in the areas between sites 1 to 4. At site
5 and areas beyond that, joint sets J1 and J2 are few, with J1 absent in
some places. Joint set J3 appears to represent unloading/stress-relief
structures that parallel the slope surface and are exposed between sites
1 to 5. The dip of joint set J4 mainly exposed at sites 1 to 5 is less
than 41°. Joint set J4 also represents unloading structures created
during denudation of the diorites and granite. Joint set J5 whose mean
dip is about 40° is mainly found at site 5 and areas beyond site 5. It
should be noted that the dip/dip direction of the joint sets at the
first four sites have very similar characteristics. In contrast, the
dip/dip direction of the joints recorded at site 5 show significantly
different characteristics including the disappearance of joint set, J1,
and the appearance of joint set, J5 (Fig. 3 and Fig. 8).