Geoscience Reference
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Table 5.6
Effect of aging (Skempton, 1988).
(N
o
)
60
/
D
r
Description
Age (years)
Laboratory tests
10
−
2
35
Recent fills
10
40
Natural deposits
10
2
55
>
•
Fills can therefore be considered medium dense with a corrected N value of 5,
while in a natural deposit, this value would be interpreted as a loose sand.
5.7 Effect of angularity and grading on strength
•
Inclusion of gradations and particle description on borelogs can influence strength
interpretation.
•
These two factors combined affect the friction angle almost as much as the density
itself as measured by the SPT N - value.
Table 5.7
Effect of angularity and grading on siliceous sand and gravel strength
BS 8002 (1994).
Particle description
Sub division
Angle increase
Angularity
Rounded
A
0
=
Sub - Angular
A
2
=
Angular
A
=
4
Grading
Uniform soil (D
60
/D
10
2)
B
0
<
=
Moderate grading (2
D
60
/D
10
6)
B
2
≤
≤
=
Well graded (D
60
/D
10
6)
B
4
>
=
Figure 5.1
Indicative variation of sand friction angle with gradation, size and density.
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