Engineering Rock Mechanics

Rock mechanics

74 interactions and rock

engineering systems

14.1 Interactions

When designing a structure to be built on or in a rock mass, it is

necessary not only to consider individual factors such as the intact rock,

fractures, rock stress, permeability, excavation and support, but also how

these all interact together. As a means of linking the rock mechanics

principles to the rock engineering applications, it is appropriate to

consider how such interactions can be characterized. For rock mechanics

modelling and rock engineering design for a specific project, we need

to be able to identify the relevant physical variables and the linking

mechanisms, and then consider their combined operation. Also, we

need to ensure that all the relevant factors and their interactions will be

taken into account.

For example, it may be determined that for a particular slope stability

study the influence of changes in rock stress on fracture aperture and

hence water flow does not need to be considered, and that the influence

of water pressure and open fractures on the rock stress is not significant

either. Thus, this aspect of hydro-mechanical coupling in the rock mass

would not be considered in the design. The key point is that we should be

aware that hydro-mechanical couplings and other interactions exist, and

make an appropriate decision about whether to consider them or not.

A systematic method for thinking about all the interactions is to list

them in a matrix. This is the basic device used by the rock engineering

systems (RES) approach (Hudson, 1992 Hudson and Jiao, 2000 2). The

principal factors considered relevant to the problem are listed along the

leading diagonal of a square matrix (top left to bottom right) and the in-

teractions between pairs of principal factors form the off-diagonal terms.

For example, in the case of just the two principal factors, Rock Stress

(X) and Water Flow (Y), there are two interactions.

'

' Hudson J. A. (1992) Rock Engineering Systems: Theory and Practice. Ellis-Horwood,

Hudson J. A. and Jiao Y. (2000) Analysis of Rock Engineering Projects. Imperial College

Chichester, 185pp.

Press, London (in preparation).