The Delft Sand, Clay & Rock Cutting Model, 2019a

Basic Soil Mechanics.
46
Friction angle versus SPT value.
44
Angle of internal friction in degrees
42
40
38
36
34
32
30
28
26
0 10 20 30 40 50 60 70 80 90 100
SPT value in blows/305 mm
Original Fitting Fitting+3 Fitting-3
Figure 2-23: Friction angle versus SPT value (Miedema (1995).
With the aim of curve-fitting, the relation between the SPT value reduced to 10 m water depth and the angle of
internal friction can be summarized to:
0.01753 SPT
51.5 25.9 e 10
(2-25)
2.4.6. The Angle of External Friction.
The external friction angle, , or friction between a soil medium and a material such as the composition from a
retaining wall or pile may be expressed in degrees as the following:
Table 2-10: External friction angle φ values.
20º steel piles (NAVFAC)
0.67·φ-0.83·φ
USACE
20º steel (Broms)
3/4·φ
concrete (Broms)
2/3·φ
timber (Broms)
2/3·φ
Lindeburg
2/3·φ
for concrete walls (Coulomb)
The external friction angle can be estimated as 1/3·φ for smooth retaining walls like sheet piles or concrete surfaces
against timber formwork, or as 1/2·φ to 2/3·φ for rough surfaces. In the absence of detailed information the
assumption of 2/3·φ is commonly made.
Copyright © Dr.ir. S.A. Miedema TOC Page 31 of 454