Farhad Salour Doctoral Thesis

7.
 
Summary of the Papers 
7.1.
 
Paper I and II 
The appended papers present environmental data measurements, analyses and findings 
from the field studies carried out in the Torpsbruk test site along county road 126 in 
southern Sweden (Figure 17). The pavement structure consists of a 100 mm thick HMA 
layer (dense graded mix, 16 mm maximum grain size and 160/220 bituminous binder 
penetration grade) with 160 mm crushed gravel base and 300 mm natural sandy gravel 
subbase layers. The subgrade soil at the test section is classified as sandy silt material 
with more than 25% fines content resting on bedrock layer at 3.0 to 3.5 m depth. 
Pavement environmental factor data collection mainly consisted of groundwater level 
sensors (six groundwater rods with automatic data logger in the transverse direction of 
the road), subsurface volumetric moisture content sensors (four moistures rods each 
consisting of four sensors with automatic data logger) and temperature sensors (one 
frost rod). A schematic overview of the test site instrumentation is illustrated in Figure 
18. The structural response of the pavement was measured using a trailer-mounted 
KUAB FWD device with multilevel loads. 
FIGURE 17. 
Location of the Torpsbruk test site along county road 126 in southern 
Sweden.
 

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FIGURE 18.
 
Schematic overview of the pavement instrumentations (GW: groundwater 
probes, MC: Moisture content probes). 
Paper
I
mainly focuses on investigating the structural behaviour of the pavement 
system during the spring-thaw period in 2010 (Figure 19). During the study period, the 
pavement profile subsurface temperature and moisture content were measured and the 
structural behaviour of the pavement was assessed using frequent FWD measurements. 
Figure 20 shows the deflection basin variations during the thawing and the recovery 
periods in 2010. As thaw penetrated the pavement structure, the moisture that was 
accumulated in the pavement structure during the freezing period in the form of ice 
lenses converted back into the liquid phase. Thaw penetration broke down the particle 
ice-bonds which also releases excess moisture into the pavement system. This resulted 
in a considerable decrease in the overall stiffness of the pavement system (Figure 20, 
left). As the excess moisture was further drained out from the pavement structure, the 
unbound layers regained their pre-freezing stiffness and the pavement recovered (Figure 
20, right). 

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