Farhad Salour Doctoral Thesis

Paper
II
the moisture content of the pavement unbound layers was deliberately 
changed by increasing the groundwater level through manipulation of the drainage 
system (Figure 23). Figure 24 represents the moisture measurement in the unbound 
layers during the drainage clogging and the maximum FWD deflections corresponding 
to a 50 kN load level.
 
In this study, in addition to evaluating the effect of groundwater level and unbound 
layer moisture content on the mechanical response of the pavement structure, the stress 
sensitivity of the material was also investigated. The FWD tests during this study were 
conducted at three different load levels (30, 50 and 65 kN). A backcalculation algorithm, 
illustrated in Figure 25, was proposed that could determine stiffness model parameters 
of the unbound materials from multilevel loads FWD test data. 
Figure 23. 
Groundwater level variation due to drainage clogging (registered by 6 
groundwater probes across the road). 

---

40 
Figure 24. 
Subsurface volumetric moisture content variation in unbound layers due to 
drainage clogging and maximum 50 kN FWD deflections.
 
Figure 25. 
Backcalculation algorithm. 

---

41 
The moisture sensitivity and the stress dependency of the unbound materials were 
investigated from in situ surface deflection tests. The backcalculated granular layer and 
subgrade stiffness from the multilevel load deflection data and their corresponding 
moisture measurements are presented in Figures 26 and 27. Through the approach used 
in this case study the impact of moisture content on the material stiffness as well as its 
stress dependency could simultaneously be observed. Moisture increase in the pavement 
structure resulted in 38% and 37% reduction in the stiffness for the granular layer and 
the subgrade, respectively.