Geology Reference
In-Depth Information
The left-hand column classi
cation is used in several textbooks and standards for foundation design
(e.g., BS 8004, 1986; Tomlinson, 2001). The changes in the amended BS 5930 (right-hand column)
are inconsistent; note in particular the very different de
nitions of the termweak. Care must be taken
when interpreting boreholes to check the governing standard at the time of the works. Other terms
are used in different standards in different countries
(Table C5)
.
BS 5930: 1999; GCO (1988)
BS EN ISO 14689-1:2003; ISRM (1981);
amended BS 5930: 1999 (2010)
Term &
UCS
(MPa)
Identi
cation
Identi
cation
Term &
UCS
(MPa)
Easily crumbled by hand; indented
deeply by thumbnail.
Extremely
weak <0.5
Extremely
weak <1.0
Crumbled with dif
culty;
scratched easily by thumbnail;
peeled easily by pocket knife.
Indented by thumbnail.
Very weak
0.5
-
1.25
Broken into pieces by hand;
scratched by thumbnail; peeled by
pocket knife; deep indentations (to
5mm) by point of geological pick;
hand-held specimen easily broken
by single light hammer blow.
Crumbles under
firm blows with
point of geological hammer, can
be peeled with pocket knife.
Weak
1.25
Very weak
1
-
5
-
5
Broken with dif
culty in two
hands; scratched with dif
culty by
thumbnail; dif
cult to peel but
easily scratched by pocket knife;
shallow indentations easily made
by point of pick; hand-held
specimen usually broken by single
light hammer blow. Point load
strength (PLS) 0.2
Can be peeled by a pocket knife
with dif
Moderately
weak
5
culty, shallow
indentations made by a
Weak
5
rm
blow of geological hammer.
-
25
-
12.5
-
0.5 MPa.
Scratched by pocket knife;
shallow indentations made by
Cannot be scraped or peeled with
a pocket knife, specimen can be
fractured with single
firm blow with point of pick;
hand-held specimen usually
broken by single
Moderately
strong
12.5
Medium
strong
25
firm blow of
rm
hammer blow. Point load
strength (PLS) 0.5
-
50
-
50
geological hammer.
-
2 MPa.
Firmblows with point of pick cause
only super
cial surface damage;
hand-held specimen requires more
than one
Specimen requires more than one
blow of geological hammer to
fracture it.
Strong
50
Strong
50
-
100
-
100
firm hammer blow to
break. PLS 2
-
4MPa.
Very
strong
100
Very strong
100
Many hammer blows required to
break specimen. PLS 4
Specimen requires many blows of
geological hammer to fracture it.
-
200
-
8 MPa.
-
250
Extremely
strong
>250
Extremely
strong >200
Specimen only chipped by
hammer blows. PLS > 8 MPa.
Specimen can only be chipped
with geological hammer.
