Questions 7,1-7.10:
fractures
and hemispherical
projection
Q7. I The overall XQD for 134 m of borehole core was found to be 58%.
(a) Compute estimates for the total number of pieces of core, and the
total length of those pieces of core that could be expected to be greater
than 0.1 m long.
(b) How many pieces of core could be expected to have a length
greater than 0.2 m, and what is their mean length?
47.2 Based on a sample of 128 fracture spacing values which gave a
mean spacing of 0.215 m, estimate the range of the population mean
fracture spacing and frequency at the 80% confidence level. How many
fractures should be in the sample for an error of f10% at the 90% and
95% confidence levels?
47.3 The mean fracture frequency in a vertical direction in a sandstone
rock mass is 1.22 m-l, and a total of 500 vertical 3-m-long rockbolts are
to be installed to stabilize the roof of an underground excavation in this
rock mass. How many rockbolts would you expect to:
intersect no fractures;
intersect less than 3 fractures; and,
intersect more than 4 fractures?
What length should the rockbolts be if 95% of them are required to
intersect at least 3 fractures, i.e. extend to the fourth rock block back into
the rock mass?
47.4 A fault plane with orientation 234/56 has been discovered during
a site investigation. Closer inspection shows that it has surface lineations
which have a pitch of 78" measured from the northwest strike line. What
is the trend and plunge of these lineations?
47.5 The line of intersection between two planes trends approximately
northwest and plunges at 38". The orientation of one of the planes is