Questions and answers: fractures and hemispherical projection 1 09This shows how, by adopting the larger RQD threshold, we have almost
doubled the range of RQD in the rock mass. As a result of using this new
threshold value, RQD would be a much more discriminatory measure of
anisotropy than when the customary threshold is used.
With the discontinuity sets given, the complete variation in frequency
in all directions in three dimensions is as shown on the hemispherical
projection below. This shows that the global minimum frequency is
1.42 m-’ and the global maximum frequency is 12.48 m-l, and these
results indicate a threshold value of t* = 0.39 m.
Extreme values
0 Localminimum
0 Global minimum: 1.42
o Local maximum
+ Global maximum: 12.48Contour values
1 1 .oo
9.00
7.00
5.00
3.00-. -.. -.. -.. -. .-
......
- -.
Set normals
+ with set number3-D variation of fracture frequency.The two hemispherical projection plots below show how RQD varies
with a threshold value of 0.1 m and a threshold value of 0.39 m. For the
threshold value of 0.1 m, the global range is about 35%, whereas with a
threshold value of 0.39 m the range is about 85%; an increase of nearly
two and a half times. The contours in these plots show how the use of
the higher threshold value has increased the discrimination of RQD in
the region of the global frequency minimum.
Extreme values
0 Localminimum
0 Global minimum: 64.52
o Local maximum
+ Global maximum: 99.08
Contour values
80.00
60.00
40.00
20.00........-.
__ - - - - - - - -Set normals
+ with set number3-D variation of RQD for threshold of 0.10 m.