Farhad Salour Doctoral Thesis

Figure 3
. Factors contributing to the moisture regime and its variation in pavement 
systems. 
With respect to the moisture content, the pavement structure profile can be divided into 
several sections. Assuming that groundwater table exist at a certain depth below the 
structure, the pavement profile can be divided into two distinct zones. Above the 
groundwater table is the vadose zone in which the unbound materials are in unsaturated 
state. Below the groundwater table is the saturated zone in which all the pores are 
completely filled with water. The moisture content profile within the vadose zone varies 
from the saturated state at its base to the natural material moisture state at the upper 
extent and can be divided into three sub-zones: the capillary zone, the intermediate 
vadose zone and the surface water zone (Erlingsson et al., 2009b). In the capillary zone 
or the capillary fringe, the water from the groundwater table is pulled upwards due to 
the capillary forces. Water is almost filling all of the voids and the air phase is 
discontinuous and therefore the pore-water pressure is less than the atmospheric 
pressure. Depending on the grain size distribution and the material properties, the 
thickness of the capillary zone can vary from few centimetres up to few metres. In the 
intermediate vadose zone, the remaining of the drained water is held, also due to the 
capillary forces. In this zone both the air and the water phases are continuous. In the 

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surface water zone, air is filling most of the voids and the water phase is discontinuous 
mainly holding in form of water packs. The water content of the intermediate vadose 
zone and the surface zone can considerably vary throughout the year as water may 
infiltrate into the pavement structure during wet raining seasons and spring-thaw 
periods (Erlingsson et al., 2009b). A conceptual schematic of different regions of water 
in a pavement structure is shown in Figure 4. 
Variation in the moisture content in pavement layers, can affect the mechanical 
properties of the material through different mechanisms. In coarse-grained materials, 
increase in moisture content can reduce the inter-particle friction and contact forces due 
to water lubrication effects between the contact area of the particles. In unbound 
materials with high fines content (e.g. subgrade soils), moisture variation can 
additionally affect the state of stress of the material through pore suction and pore 
pressure effects.