Page 91 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

the percentage passing the 0.425 sieve. Coarse subbase materials showed a significant reduction in friction angle
under wet conditions when the product of the BLS and the -0.425 fraction exceeds 170.

The updated transfer function still looks at the shear behaviour of the granular layer, but uses the stress ratio rather
than the safety factor. The stress ratio is conceptually the inverse of the safety factor. The model provides for
subgrade deformation levels from 1 to 20 mm. Details of the models, and how they are implemented, are provided
in Theyse et al, 2011. The formulation of these models may change for the final SAPDM, expected in 2013.

Table 31. Revised Shear Strength Properties for Unbound Granular Materials (2008b)

Shear Strength Parameters
1
Application Material Code Saturation Level
Cohesion (kPa) Friction Angle (°)
Dry 90 – 130 53 – 57
G1 Moderate 75 – 100 51 – 55
Wet 50 – 75 50 – 53
Dry 100 – 125 54
G2 Moderate 50 52
Wet 45 50
Base
Dry 75 51
G3 Moderate 40 51
Wet 20 50
Dry 75 51
G4 Moderate 40 47
Wet 20 45
Dry 100 – 125 45 – 49
G5/6
Subbase (BLS425 < 170) Moderate 50 – 100 41 – 45
2
Coarse Materials Wet 10 – 50 39 – 42
GM: 1.7 – 2.3 Dry 225 – 275 45 – 49
Max size: 28 – 37.5 G5/6 Moderate 50 – 100 41 – 44
(BLS425 > 170)
Wet 25 – 35 31 – 33
Subbase Dry 125 – 250 43 – 45
Fine material G5/6 Moderate 40 – 50 43 – 45
GM: 1.5 – 1.6 (BLS425 < 100)
Max size: < 14 Wet 10 – 25 40 – 43
Dry 75 – 100 43 – 45
G7 Moderate 0 41 – 43
Ferricrete
0
Selected Subgrade Wet 75 – 100 40 – 41
Dry
35 – 37
G7 Moderate 0 37 – 40
Sand
Wet 0 35 – 37
Dry 75 45
G10 Moderate 0 37
Ferricrete
Wet – –
Dry 80 – 100 30 – 35
In Situ Subgrade Silt Moderate 0 30 – 35
Wet 0 30 – 35
Dry > 250 20 – 30
Clay Moderate 25 – 50 15 – 25
Wet 5 – 25 10 – 15
Notes:
1. Dry = 20% Moisture
Moderate = 50% Moisture
Wet = 80% Moisture
2. BLS425 = Product of the bar linear shrinkage and percentage passing the 0.425 mm sieve

Section 7: Structural Capacity Estimation: Flexible Pavements
Page 80