Farhad Salour Doctoral Thesis

1.2.
 
Objective and scope of the research 
The aim of this study was to improve knowledge about the impact of moisture content 
and its seasonal variation on the structural response of pavement structures. More 
precisely, the in situ and laboratory response of pavement unbound layers and silty sand 
subgrade soils with respect to change in the moisture content were of interest. In the 
laboratory-based studies in particular, an attempt was made to take into account the 
unsaturated condition of the soil (i.e. incorporating soil suctions) in mechanical 
response modelling of the material. The specific objectives at different stages of the 
research project within the overall vision of the study were as follows: 
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Monitoring short term and long term seasonal variations in groundwater level, 
pavement profile temperature and moisture content through field 
instrumentation. 
–
Investigating the influence of environmental factors on pavement layers 
mechanical response and overall stiffness based on field measurements. 
–
Examining the efficiency of the subsurface drainage system in removing the 
excess moisture from the pavement structure for possible improvement 
considerations. 

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Analysing the moisture sensitivity and stress dependency of the granular base 
and subbase material and subgrade soil through backcalculation of the surface 
deflection data. 
–
Studying the feasibility of backcalculating material behaviour model parameters 
from multilevel loads FWD measurements. 
–
Understanding the effect of soil suction on the resilient behaviour of silty sand 
(SM) subgrade soils with high fines content. 
–
Investigating several laboratory based suction-resilient modulus predictive 
models and implementing the modified models for silty sand (SM) subgrade 
materials. 
–
Evaluating the laboratory based suction-resilient modulus models with field 
measurements and FWD data. 
–
Feasibility study of using multistage RLT tests for permanent deformation 
characterization and modelling of fine-grained subgrade materials.
–
Investigating the effect of moisture content variation on the permanent 
deformation characteristics of silty sand subgrade soils. 
To achieve the objectives of the study, both field and laboratory based studies have been 
carried out. In the following, a summary based on the six appended journal papers are 
presented. 

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