Page 111 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Zone 1: Zone 2: Zone 3:
Positive Curvature Reverse
curvature inflection curvature

Figure 44. Zones of a Deflection Bowl

Table 45. Behaviour States for Granular Base Pavements
Behaviour Traffic Range Maximum BLI MLI LLI
State (MESA) Deflection (mm) (mm) (mm)
(mm)
Very stiff 12 – 50 < 0.3 < 0.08 < 0.05 < 0.04
Stiff 3 – 8 0.3 – 0.5 0.08 – 0.25 0.05 – 0.15 0.04 – 0.08
Flexible 0.8 – 3 0.5 – 0.75 0.25 – 0.5 0.15 – 0.2 0.08 – 0.1
Very flexible < 0.8 > 0.75 > 0.5 > 0.2 > 0.1

Table 46. Deflection Bowl Parameter Structural Condition Rating Criteria
Pavement Structural Deflection Bowl Parameters
Base Type Condition
Rating Ymax RoC BLI (mm) MLI (mm) LLI (mm)
Sound < 500 > 100 < 200 < 100 < 50
Granular base Warning 500 – 750 50 – 100 200 – 400 100 – 200 50 – 100
Severe > 750 < 50 > 400 > 200 > 100
Sound < 200 > 150 < 100 < 50 < 40
Cementitious
base Warning 200 – 400 80 – 150 100 – 300 50 – 100 40 – 80
Severe > 400 < 80 > 300 > 100 > 80
Sound < 400 > 250 < 200 < 100 < 50
Bituminous
base Warning 400 – 600 100 – 250 200 – 400 100 – 150 50 – 80
Severe > 600 < 100 > 400 > 150 > 80

The following comments apply to the use of the deflection bowl analysis method:
• The method is an empirical method that was calibrated for South Africa pavements and conditions.
• The method allows for different pavement types.
• The method should therefore be used with caution as a rough indication of the remaining structural
capacity of pavements.
• The use of deflection bowl parameters allows for the assessment of the adequacy of at least three zones
within the pavement, from the upper layers to the subgrade.
• The method is based on the FWD, which is currently the preferred deflection test instrument at network and
project level.

Section 7: Structural Capacity Estimation: Flexible Pavements
Page 100