Geoscience Reference
In-Depth Information
•
Rockmodulus correlations and the above general relationship should be calibrated
with local conditions.
•
The Brisbane relationships are from laboratory measurements.
11.20 Rock mass modulus derived from the intact rock
modulus
•
Reduction factors needs to be applied to use the intact rock modulus in design.
•
When the Young's modulus of the in-situ rock
=
E
r
E
r
=
K
E
E
i
where E
i
=
Intact rock modulus.
Table 11.20
Modulus reduction ratio (after Bieniawski, 1984).
RQD (%)
Modulus reduction ratio, K
E
0-50
0.15
50-70
0.2
70-80
0.30
80-90
0.40
>
90
0.70
11.21 Modulus ratio based on open and closed joints
•
The modulus ratio (intact rock modulus/rock mass modulus) can be derived from
the RQD combined with the opening of the rock joints, if known.
•
Open joints have a higher reduction value at high RQD values.
Table 11.21
Estimation of the rock modulus based on the RQD values (after
Carter and Kulhawy, 1988).
RQD (%)
K
E
E
i
/E
r
=
Closed joints
Open joints
20
0.05
50
0.15
0.10
70
0.70
100
1.00
0.60
11.22 Rock modulus from rock mass ratings
•
The modulus values can be derived from rock mass ratings systems (described in
later sections).
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