Page 124 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

(ii) Support Stiffness
The first step in determining the stiffness of the support layers is to identify the type of subbase and subgrade, and
the subbase thickness. Recommended stiffness values for the materials types are given in Table 51. To determine
the equivalent support stiffness from subgrade and subbase, the nomograph in Figure 50 is used.

Table 51. Stiffness Moduli for Support Layers
Material and Stiffness Value (MPa)
Material Class
PCC 30 000 to 50 000
Asphalt 1 500 to 5 000
Cemented 1 500 to 15 000
1
G1 250 to 750 (400)
G3 150 to 400 (200)
Granular G5 100 to 250 (130 for subgrades)
G7 50 to 160 (90 for subgrades)
G9 30 to 80 (50 for subgrades)
Note
1. Recommended value in parenthesis

Figure 50. Nomograph for Determining Equivalent Stiffness

Section 7: Structural Capacity Estimation: Concrete Pavements
Page 113