244 Rock mechanics interactions and rock engineering systemsment or providing drains, will be appropriate to other circumstances
depending on the system being studied.
This type of instability inhibition through identification and mitigation
of the key mechanisms in potential positive feedback loops in the sys-
tem structure will be effective in reducing engineering hazards. However,
a complete study of all the positive feedback effects requires an under-
standing of the operation of the complete system. The off-diagonal terms
in the interaction matrices presented so far represent the structure of the
system, i.e. the interactions in isolation before the system is 'switched on'.
For a linear system, it is possible to establish the coupled interactions (Jiao
and Hudson, 1998 6), i.e. the interaction between two principal factors or
variables when all interactions are operating and influencing one another.
These coupled interactions are not the same as the isolated interactions.
14.3 Additional points
Once the variables and mechanisms required to capture the essence
of a problem have been identified, modelling procedures, potential
numerical codes available for use, and rock engineering designs can
be technically audited for their content. Note that there can be no
standardized modelling procedures, nor standardized site investigation
and designs, because both will depend on the modelling and design
objectives. Indeed the very essence of good modelling and design is to
be flexible and adapt to the project circumstances. The result is that all
projects are different and it is by no means clear in many cases that all
the factors have been adequately taken into account in the design.
Thus, the implementation of technical auditing for all these purposes
is to establish whether a model, particular numerical code, or design has
incorporated the required variables and mechanisms needed to model
the project circumstances. The principles of technical auditing are as
follows (Hudson, 1999 7).
(1) Technical Auditing (TA) is the process of establishing whether
rock engineering measurements, statements and conclusions can be
considered to be valid.
(2) There is a requirement for a TA if there is a need to establish
the reliability and credibility of information, or if there is a public
interest dimension requiring public accountability.
(3) TA differs from Quality Assurance (QA) because QA per se is only
concerned with following pre-determined procedures, regardless
of whether the procedures are right or wrong. TA checks that
the technical content is adequate for the purpose and hence is a
pre-cursor to establishing the appropriate QA procedures.6The methodology used for this technique is described in Jiao Y. and Hudson J. A.
(1998) Identifying the critical mechanisms for rock engineering design. Gotechnique, 48,' Hudson J. A. (1999) Keynote lecture: technical auditing of rock mechanics modelling
and rock engineering design, in Proc. 37th US Rock Mechanics Symposium held at Vail, CO,
1999 (B. Amadei, R. L. Kranz, G. A. Scott and P. H. Smeallie, Eds). Balkema, Rotterdam,3,319-335.pp. 3-12.