AbstractIn BS 5930:1981 both the state of weathering of rock
material and a scale of weathering grades for the rock mass
are included in a Code for the first time. The schemes
proposed are largely derivative from those proposed by
Working Parties of the Engineering Group, which in turn
benefited from earlier studies in Hong Kong and Australia.The descriptive terms used for rock material: fresh,
discoloured, decomposed, disintegrated, are defined, and the
stages of weathering subdivided using qualifying terms, for
example 'partially discoloured'. These descriptive qualifying
terms may be quantified if necessary, but no indication is
given as to how this should be done.Following recent Australian practice, the scale of
weathering grades of the rock mass is described in the terms
applied to the rock material. Except in the case of Grade 1,
Fresh, discontinuities and other defects of the rock mass are
not mentioned. This implies, and it needs emphasizing, that
the descriptive terms for the degree of weathering should
provide a reliable indication of the effects of weathering on
the engineering properties or engineering behaviour of the
rock mass. The material and the defects, such as
discontinuities in the rock mass, therefore need to be
described separately.A descriptive scheme is proposed for the simple definition
of weathering classes of rock material, and application of
these classes to the description of the rock mass is also
considered.The effect of scale, particularly the spacing of discontinuities
and thickness of highly weathered zones, is
important in assessing the engineering properties of the rock
mass. This can be dealt with effectively in the descriptive
logging of drill core and rock exposures.