Table 3.  Design Thicknesses for CBM Base for More than 80,000,000 ESALs

 11

The Danish Road Institute (Report 138) 

 

In 2004, the Danish Road Institute published a mechanistic design guide for semi-rigid 

pavements (Thogersen et al., 2004).  This mechanistic guide was developed as a result of a 

survey that showed the superior performance of pavements with CTB, especially on heavily 

trafficked pavement sections.  In order to understand the behavior of such pavements and 

establish a mechanistic design, a full-scale test on six semi-rigid pavements (three different types, 

each with two replications) was carried out.  A generalized incremental-recursive model based 

on tensile strain at the bottom of the CTB layer was chosen as the desired approach to verify the 

deterioration model (Thogersen et al., 2004).  The results were then compared to existing semi-

rigid pavements that had been in service for more than 20 years.  The comparison of these results 

showed that the deterioration model was accurate. 

 

 

The study focused on the failure of the semi-rigid structure in terms of fatigue of the rigid 

layer.  The determining factor in the fatigue damage was the longitudinal (tensile) strain at the 

bottom of the CTB layer.  The investigation concluded that for their semi-rigid pavement 

structure, at 75 percent confidence, the following deterministic design criterion should be used to 

prevent fatigue failure of the structure: 

 

 

 

( )

0.12

6

PERMISSIBLE

N

99 str

10

−

ε

= μ ×

(10)

 

 

where 

 

 

PERMISSIBLE

ε

 = maximum strain at bottom of CTB layer 

 

μstr 

= micro-strain (10

-6

 strain) 

 

N = number of load repetitions (passes) to failure. 

 

 

Once the mechanistic behavior of the semi-rigid structure was modeled, the criterion 

constants were utilized to provide designs for various traffic volumes (Thogersen et al., 2004).  

In the design table (Table 5), the load is represented as a dual-wheel load with 20 % dynamic 

load additions as used in the new Danish design standards. 

 

 12

Table 5.  Semi-rigid Pavement Design for the Danish Road Institute (Thogersen et al., 2004) 

tải về 1.81 Mb.

Chia sẻ với bạn bè của bạn: