Geoscience Reference
In-Depth Information
Rock strength parameters from
classification and testing
6.1 Rock strength
There are many definitions of strengths.
The value depends on the extent of confinement and mode of failure.
Table 6.1 Rock strength descriptors.
Rock strength
Description
Intact strength
Intact specimen without
any defects
Rock mass strength
Depends on intact strength factored
for its defects
Tensile strength
5% to 25% UCS - use 10% UCS
Flexural strength
2
×
tensile strength
Point load index strengths
UCS/20 but varies considerably.
A tensile test
Brazilian strengths
A tensile test
Schmidt Hammer strengths
Rebound value. A hardness test
Unconfined compressive strengths
A compression test strength under
uniaxial load in an unconfined state
UCS or q u
Soft rock
UCS
10 MPa
<
Medium rock
UCS
10 to 20 MPa
=
Hard rock, typical concrete strength
UCS
20 MPa
6.2 Typical refusal levels of drilling rig
The penetration rate, the type of drilling bit used and the type and size of drilling
rig are useful indicators into the strength of material.
Typical materials and strengths in south east Queensland is shown in the table.
 
 
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