Farhad Salour Doctoral Thesis

Figure 16.
M
R
-Moisture model proposed in MEPDG (ARA, 2004). 
Full-scale accelerated pavement testing
 
Erlingsson (2010) conducted a study based on Accelerated Pavement Testing (APT) of 
an instrumented thin flexible pavement to investigate the influence of the moisture 
content on the performance of the pavement structure. In this study 1000,000 wheel 
load passages were applied using a Heavy Vehicle Simulator (HVS) on a typical flexible 
pavement structure in which 500,000 of the load passages were conducted while the 
pavement structure was in its natural moisture condition and 500,000 load passages 
were conducted after the groundwater table was raised to 30 cm below the top of the 
subbase. From the measurements and the numerical analyses of the data it was 
observed that introducing the water to the system resulted in larger permanent and 
resilient strains in all the unbound layers. In similar studies by Saevarsdottir and 
Erlingsson (2013a and 2013b), it was also observed that all the unbound layers showed 
increased permanent and resilient deformations as the moisture content increased, with 
the most dramatic increase in the subgrade layer. 
6.2.
 
Field-based investigation and measurements 
The considerable influence of environmental factors on the performance of pavement 
structures has led to significant effort in in situ measurement of these parameters. 
Several highway agencies around the world have initiated seasonal monitoring data 
collection as part of their Long-Term Pavement Performance (LTPP) programs to 

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determine climatic factor effects on performance of pavement systems. These data 
bases can consist of weather stations data, pavement moisture content and temperature 
profile monitoring as well as frost penetration and frost-heave measurements (Jong et 
al., 1998; Janoo and Shepherd, 2000; Erlingsson et al., 2002; Savard et al., 2005; Zapata 
et al., 2009). 
In an 18-month field survey on three instrumented highways in the state of Wisconsin, 
Jong et al. (1998) monitored the pavement moduli changes caused by seasonal climatic 
variations. They reported up to 4 and 12 times increase in the subgrade and base layer 
moduli, respectively, as frost penetrated into the pavement structure. They observed a 
clear correlation between the in situ moisture content and the stiffness of unbound 
layers. The base and subgrade layer moduli were decreased by 35 and 65 percent, 
respectively, due to an increase in the moisture content at the end of the thawing period 
compared to the pre-freezing measurements. 
Janoo and Shepherd (2000) analysed the subsurface moisture and temperature data as 
well as the surface deflection measurements collected from ten sites across the state of 
Montana to measure in situ subgrade moduli and their seasonal variation. Significant 
variation in unbound layer moisture content and layer moduli was observed from the 
field measurements. Using the deflection data, they recommended a model that could 
predict the subgrade stiffness as a function of temperature and volumetric moisture 
content to be used in future mechanistic design practices. They also suggested critical 
load-restriction time periods during spring-thaw weakening based on the temperature 
and moisture measurements. 
In a field study conducted by Erlingsson et al. (2002), temperature and moisture 
variability of three road sections in south-west Iceland were monitored during a three 
year period. A significant long and short term volumetric moisture content variation 
was observed due to the freeze-thaw conditions and the precipitation. The layer moduli 
backcalculation from the FWD showed a strong correlation with the measured moisture 
content. 

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