CHAPTER 5 CONCRETE PAVEMENTS - TU Delft

Subgrade k0 (N/mm 3 )
Well graded gravel and gravel/sand-mixtures, hardly any fine material
Poor graded gravel, hardly any fine material
Gravel/sand/clay-mixtures
Well graded sand and sand with gravel, hardly any fine material
Poor graded sand, hardly any fine material
Sand/clay-mixtures
Very fine sand, sand with loam
Vast clay
Weak clay and peat
Table 5.2: Rough k0-values for various types of subgrade (2).
0.08 – 0.13
0.08 – 0.13
0.05 – 0.13
0.05 – 0.10
0.04 – 0.10
0.03 – 0.08
0.03 – 0.05
0.01 – 0.03
0.00 – 0.01
When the CBR-value of the subgrade is known, then an indication of the ko-value can
also be obtained by means of figure 5.6.
Figure 5.6: Rough relationship between ko and CBR for various types of subgrade (2)
As already mentioned in paragraph 5.2, generally a sub-base and/or a base are
constructed over the subgrade. The effect of these layers can be estimated by means
of figure 5.7.
The k-value at the top of a layer is found from the k-value at the top of the underlying
layer and the thickness hf (mm) and the dynamic modulus of elasticity Ef (N/mm²)
(table 5.3) of the layer under consideration. This procedure has to be repeated for
each (sub-)base layer, so at the end the ‘modulus of substructure reaction’ k on top
of the substructure, i.e. directly beneath the concrete top layer, is found.
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