Farhad Salour Doctoral Thesis

Figure 15.
Schematic demonstration of the time-hardening concept (Erlingsson and 
Rahman, 2013). 
If the time-hardening concept is applied to the generalized single stage permanent 
deformation model (given in Equation 6), the following generalized equation for 
multistage RLT tests is obtained: 
 
)
,
,
(
)
(
ˆ
2
1
1
i
r
i
i
eq
i
i
pi
q
p
f
N
N
N
f
N






[7] 
In this approach, the data from a multistage RLT test on a single specimen can be used 
to obtain the optimized set of material parameters for the selected permanent 
deformation model. 

---

31 
6.
 
Moisture Effects on Unbound Materials and Subgrade Soils 
Unbound granular materials and subgrade soils significantly contribute to the overall 
bearing capacity of pavement structures. The material characteristics of unbound layers 
and subgrade soils are therefore of great importance in the performance of pavement 
systems. Although pavement systems are ideally designed to remain as drained as 
possible, moisture is usually present in pavement structures and the unbound layers are 
often in a partially saturated state. Even pavement structures with good drainage 
systems can experience periods with excess moisture presence such as (e.g. heavy rain 
events and a spring-thaw period in cold regions). 
The significant detrimental effects of moisture content on the behaviour of unbound 
materials are well-known (Cary and Zapata, 2010; Erlingssson, 2010; Saevarsdottir and 
Erlingsson, 2013a). In coarse-grained granular materials an increase in moisture content 
can result in reduction in the resilient modulus due to decreased contact friction and