Estimates of the equivalent foundation modulus derived by Mayhew and
Harding are detailed in Table 8.2 for different subbase materials and subgrade
CBRs.
The slab thicknesses derived from Equations 8.5 and 8.6 are for concrete
pavements that, under fully trafficked conditions, have a 50% probability of
achieving the service life specified. A highway engineer may require a design
incorporating a higher probability of survival; 85% is considered generally
acceptable.
In order to increase the probability of survival, the slab thickness derived in
either of the above equations should be increased by the value indicated by the
graph in Fig. 8.10