Engineering Rock Mechanics

Testing techniques

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11.1 Rock properties

The term ’rock properties’ refers here to those intact rock or rock

mass properties that are needed for engineering design purposes. For

example, the rock properties may be used to

obtain a general impression of the mechanical nature of the rock

mass, e.g. the rock is strong because it has a compressive strength of

300 MPa,

compare the rock properties with a previous project where the rock

properties were also obtained, e.g. this rock is stronger than the one

we had at the Golconda Mine,

0 generate a rock mass classification scheme value, e.g. the RQD is

needed for the Rock Mass Rating (RMR) scheme, see Chapter 12, or

support numerical modelling, e.g. the shear stiffness of fractures is

required for a distinct element numerical code.

Many of the required rock properties can be categorized according to the

subjects of the earlier chapters, as shown in Table 11.1.

Strictly speaking, in situ stress is a site property rather than a rock

property, but testing techniques are required to determine the in situ

stress and so it is one of the categories below. The ’permeability’ could

be included as a separate item under each of the ’intact rock’, ’fractures’

and ’rock mass’, but we prefer to consider the property in a separate

category because the subject involves the connectivity of the rock mass

fractures. In each case, there should be information about any variation

in these properties across the site, which was the theme of Chapter 10.

Table 11.1 Examples of rock properties measured in a site investigation programme

In situ stress Intact rock Fractures Rock mass Permeability

Magnitudes and Deformation, Geometrical Deformation, Nature of any
directions of the strength and occurrence and strength and flow through
three principal failure mechanical failure the intact rock
stresses properties properties properties and rock mass