Engineering Rock Mechanics

Additional points 2 1 3

can be written in the form
SMR = RMR- Fg + Fe,
where Fg is a factor representing the geometry of the potential instability
present in a rock slope, and F, is a factor corresponding to the excavation
method. Geometries that are intrinsically more unstable have higher
values of Fg (and hence reduce SMR), and excavation methods that
induce little perturbation in the rock mass have high values of Fe (and
hence increase SMR).
Additional work on applying classification systems to slope stability
has been reported by Sonmez and Ulusay (1999)6. In this paper, it is
noted that the rock mass classification should refer not to the rock mass
in its undisturbed condition but to the excavation-disturbed rock mass

• which is the one that hosts the rock engineering structure. The authors
  suggest methods for assessing the excavation disturbance effect on rock
  mass classification values.

the rock mass quality can be assessed simply, rapidly and continu-

the classification values can be established by trained site personnel

(i.e. a high level of general engineering expertise is not required),

continuous rock mass assessment using logging sheets will alert con-

tractors and consulting engineers to significant changes in rock condi-

tions, and

engineering design is coherently based on previous experience.

The disadvantages of using a rock mass classification system are that

the systems currently in use are historical and idiosyncratic,

the algebra and ratings values of the systems have not been scientific-

they cannot be used for the full range of engineering objectives.

The advantages of using rock mass classification systems are that

ously,

ally considered, and

Sonmez H. and Ulusay R. (1999) Modifications to the geological strcngth index (GSI)

and their applicability to stability of Slopes. Int. J. Rock Mech. Min. Sci., 36, 743-760.