Geology Reference
In-Depth Information
Outcrop
Length of
Line Sections >0.1m
Total Length of Scan Line
RQD =
x 100
0.11 + 0.2 + 0.15 + 0.28
1.00
x 100%
RQD =
RQD = 74%
11
20
7
15
95
28
5
Total length of line scan = 1.0 m
Figure 10.13 Estimating the Rock Quality Designation (RQD) from outcrop.
Measure a horizontal distance across the rock face (for example, 1.0m) and sum
the number of discontinuity intersections of spacing greater than 0.1m (high-
lighted red). Then divide by 1.0 and multiply by 100 to get %RQD.
step of the process involves calculating two Hoek Brown parameters m and s .To
do this, look at Table 10.3. It is a list of equations that together tell you all you
need to know about the key mechanical and geotechnical properties of a rock
mass including cohesion and friction angle. The example below (Figure 10.14)
shows how to calculate the numerical values of s and m in the field with the
help of a calculator (or even better a laptop and spreadsheet). Values for the
intact compressive strength (
c ) and the Hoek Brown variable m i are given in
Table 10.4. The entire process is summarised in Figure 10.15.
To gain a comprehensive overview of the rock mass condition and charac-
teristics, the RMR can be calculated both horizontally and vertically for each
segment of the rock mass under investigation. The horizontal and vertical RMR
σ
 
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