Typical relationships for estimating
the angle of internal friction, f, are as follows:
Empirical values for f, of granular soils based on the standard penetration
number, (from Bowels, Foundation Analysis).
|
SPT
Penetration, N-Value (blows/
foot)
|
f (degrees)
|
|
0
|
25
- 30
|
|
4
|
27
- 32
|
|
10
|
30
- 35
|
|
30
|
35
- 40
|
|
50
|
38
- 43
|
Relationship between f, and standard penetration number for sands, (from Peck
1974, Foundation Engineering Handbook).
|
SPT
Penetration, N-Value (blows/
foot)
|
Density
of Sand
|
f (degrees)
|
|
<4
|
Very
loose
|
<29
|
|
4
- 10
|
Loose
|
29
- 30
|
|
10
- 30
|
Medium
|
30
- 36
|
|
30
- 50
|
Dense
|
36
- 41
|
|
>50
|
Very
dense
|
>41
|
Relationship between f, and standard penetration number for sands, (from Meyerhof
1956, Foundation Engineering Handbook).
|
SPT
Penetration, N-Value (blows/
foot)
|
Density
of Sand
|
f (degrees)
|
|
<4
|
Very
loose
|
<30
|
|
4
- 10
|
Loose
|
30
- 35
|
|
10
- 30
|
Medium
|
35
- 40
|
|
30
- 50
|
Dense
|
40
- 45
|
|
>50
|
Very
dense
|
>45
|
Correlation between SPT-N value, friction angle, and relative density
|
Correlation between SPT-N value
and friction angle and Relative density (Meyerhoff 1956)
|
|||
|
SPT N3
[Blows/0.3 m - 1 ft] |
Soi packing
|
Relative Density [%]
|
Friction angle
[°] |
|
< 4
|
Very loose
|
< 20
|
< 30
|
|
4 -10
|
Loose
|
20 - 40
|
30 - 35
|
|
10 - 30
|
Compact
|
40 - 60
|
35 - 40
|
|
30 - 50
|
Dense
|
60 - 80
|
40 - 45
|
|
> 50
|
Very Dense
|
> 80
|
> 45
|
Typical values of shear strength |
|
Undrained
shear strength
|
su (kPa)
|
|
|
Hard
soil
|
su > 150 kPa
|
|
|
Stiff
soil
|
su = 75 ~ 150 kPa
|
|
|
Firm
soil
|
su = 40 ~ 75 kPa
|
|
|
Soft
soil
|
su = 20 ~ 40kPa
|
|
|
Very
soft soil
|
su < 20 kPa
|
|
|
Drained
shear strength
|
c´ (kPa)
|
f´ (deg)
|
|
Compact
sands
|
0
|
35° -
45°
|
|
Loose
sands
|
0
|
30° -
35°
|
|
Unweathered
overconsolidated clay
|
||
|
critical
state
|
0
|
18° ~
25°
|
|
peak
state
|
10 ~
25 kPa
|
20° ~
28°
|
|
residual
|
0 ~ 5
kPa
|
8° ~
15°
|
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