Page 95 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

The resilient properties (elastic moduli) for cemented materials are shown in Table 34, along with recommended
material properties for the damage models. The damage models for crush initiation, advanced crushing and effective
fatigue are given in Equations (25) and (26) in Table 35. The relationship to account for layer thickness and the time
for crack propagation, used with the effective fatigue transfer function, is also given in Equation (27) in Table 35.
Note that C1 and C2 cemented layers are not commonly used anymore, as the high cement content results in
significant cracking and consequent reflection cracking.

Table 34. Elastic Moduli and Material Properties for Cemented Materials in 1996 SAMDM
Initial Class Modulus Strain-at- UCS Equivalent Modulus
(MPa) Break (ε b ) (kPa) Granular Class (MPa)
C3 2 000 125 2250 EG4 300
C4 1 500 145 1125 EG5 200

Table 35. Transfer Functions for Cemented Materials

Crush Initiation and Advanced Crushing

σ v
�
a�1− b UCS (25)
N = 10
ci/ca

= Standard axles to crack initiation or advanced crushing
where N ci/ca
σ v = Vertical compressive stress at top of layer
UCS = Unconfined compressive strength (kPa), recommended values in
Table 34
a, b = Constants, given below
Effective Fatigue

ε
c�1− � (26)
N eff = SF •10 d ε b

= Effective fatigue life
where N eff
ε = Horizontal tensile strain at bottom of layer (microstrain)
= Strain-at-break, recommended values in in Table 34
ε b
c, d = Constants, given below
SF = Shift Factor for crack propagation (see below)
t = Layer thickness
Shift Factor (SF) to Account for Layer Thickness (t)
Thickness Shift Factor
< 102 mm 1
102 mm to 319 mm 10 (0.00285t – 0.293) (27)
> 419 mm 8
Constants
Reliability Level Crush Initiation Advanced Crushing Effective Fatigue
a b a b c d
50% (Category D) 8.216 1.21 8.894 1.31 7.06 7.86
80% (Category C) 7.706 1.31 8.384 1.23 6.87 7.66
90% (Category B) 7.506 1.10 8.184 1.20 6.84 7.63
95% (Category A) 7.386 1.09 8.064 1.19 6.72 7.49

(ii) SAPDM
Recent research by Theyse has suggested new input parameters for cement stabilized materials. These input
parameters are used with the existing transfer functions (Equation (20) in Table 30 and Equation (26) in Table 35).
Refer to Theyse (2008b), for further information. These new inputs are not yet commonly used.

Section 7: Structural Capacity Estimation: Flexible Pavements
Page 84