In the UK, deflection histories for highways have been derived from the monitoring of deflection for flexible pavements. Research Report 833 (Kennedy
et al., 1978a) developed performance charts relating deflection to cumulative
traffic for three different types of roadbase: granular, cement bound and bituminous. The relationships had been found to be valid for subgrade CBR ranging
from 2.5 to 15. Each illustrates deflection trends from its construction to the
onset of structurally critical conditions, referred to above as the investigatory
phase, and contains four envelope curves relating to different probabilities that
the critical life of the pavement will be attained (the point at which strengthening will be required to prolong its useful life)