Geology Reference
In-Depth Information
latest move in this sad story is that Eurocode 7 has reverted to a mass
scheme for classi
cation, which is essentially the same as the ISRMbut
with different zone numbers and even poorer de
nitions
(Table C9)
.
For most countries, this is relatively unimportant, but where the engi-
neering geologist
finds himself dealing with severely weathered rock,
he will probably
find it useful to adopt the approaches used in Hong
Kong and in Singapore (refer to GCO (1988), Anon (1995), BS
5930:1999 and CP3 (2004)).
Other schemes are used in different countries; many of these have
been prepared from agricultural or soil science perspectives and some
are discussed by Selby (1993). In Japan and Korea, distinctions
are made between hard rock, soft rock and weathered rock. In
China, a pragmatic classi
cation is used based on the ability to cut
material with a shovel
(Table C10)
.
As discussed at length in Anon (1995) and adopted by BS5930: 1999
and Eurocode 7, weathering in limestone needs special consideration,
as do rocks that weather in a relatively uniformway, such as chalk and
some mudstones. Norbury
(2010)
discusses
these
schemes
comprehensively.
Classi
cation is essentially a practical mass scheme, which does not deal with weathered rock masses
that develop as corestone-rich pro
les. Not applicable for core logging in boreholes.
TERM
DESCRIPTION (SIMPLIFIED
FROM ORIGINAL)
COMMENT
RESIDUAL SOIL
Structure fully destroyed. Easily dug
with shovel.
Actually, many residual soils are quite
strong, cemented with iron especially,
so can be quite dif
cult to dig.
FULLY
WEATHERED
Structure basically destroyed but still
recognisable. Residual structural
strength existing. May be dug with
shovel.
HIGHLY
WEATHERED
Majority of structural planes
destroyed. May be dug with shovel.
From experience inHong Kong, highly
decomposed (weathered) rock often
shows the highest degree of fracturing
-
they become healed by the comple-
tely weathered and residual soil stages
(Hencher &Martin, 1982).
MODERATELY
WEATHERED
Structure partially destroyed; sec-
ondary minerals along joints;
weathered
fissures developed. Hard
to cut with shovel.
NON-WEATHERED
Structure basically unchanged.
