Environmental Engineering Reference
In-Depth Information
TABLE 5.20
Suggested Hardness Classification for Intact Rock
a
Class
Hardness
Field test
Strength
b
tsf
I
Extremely hard
Many blows with geologic hammer
2000
required to break intact specimen
II
Very hard to hard
Hand-held specimen breaks with
2000-700
hammer end of pick under more
700-250
than one blow
III
Moderate
Cannot be scraped or peeled with knife,
250-100
hand-held specimen can lie broken with
single moderate blow with pick
IV
Soft
Can just be scraped or peeled with
100-30
knife. Indentations 1-3 mm deep shown
in specimen with moderate blow of pick
V
Very soft
Material crumbles under moderate
30-10
blow with sharp end of pick and can be
peeled with a knife, but is too hard to
hand-trim for triaxial test specimen
a
After ISRM Working Party,
Int. Sec. Rock Mech
., Lisbon, 1975.
b
Uniaxial compressive strength (Core Logging Comm.,
Bull. Assoc. Eng. Geol
., XV, 295-328, 1978.
TABLE 5.21
Suggested Classification for Weathered Igneous and Metamorphic Rock
a
Grade
Symbol
Diagnostic Features
Fresh
F
No visible sign of decomposition or
discoloration. Rings under hammer impact
Slightly weathered
WS
Slight discoloration inward from open fractures,
otherwise similar to F
Moderately weathered
WM
Discoloration throughout. Weaker minerals such
as feldspar decomposed. Strength somewhat less
than fresh rock, but cores cannot be broken by
hand or scraped by knife. Texture preserved
Highly weathered
WH
Most minerals to some extent decomposed.
Specimens can be broken by hand with effort or
shaved with knife. Core stones present in rock
mass. Texture becoming indistinct but fabric
preserved
Completely weathered
WC
Minerals decomposed to soil but fabric and
structure preserved (saprolite). Specimens easily
crumbled or penetrated
Residual soil
RS
Advanced state of decomposition resulting in
plastic soils. Rock fabric and structure
completely destroyed. Large volume change
a
After ISRM Working Party,
Int. Soc. Rock Mech
., Lisbon, 1975.
provide information equivalent to that obtained by field examination of large exposures,
although ideal situations combine core recovery with exposure examinations.
Building Codes
Many codes classify rock in terms of hardness using nomenclature such as sound, hard,
medium hard, and soft, but without defining the significance of the terms. The New York
