Pavement behaviour evaluation during spring thaw based on the falling weight deflectometer method

University essay from KTH/Transportvetenskap


The bearing capacity of a road decreases greatly during spring

thaw, when the previously frozen road begins to thaw. The extent of this

decrease can be evaluated by making Falling Weight Deflectomter (FWD)

measurements on the road, measuring the deflection of the road when an

impact load is applied to it. The bearing capacity of the road can then be

evaluated by backcalculating the layer modules with backcalculation

programs, or through more simple calculations based on the deflection basin

indices. Both analyses were carried out in this thesis with data from FWD

measurements which were carried out on county road Lv 126 in Southern

Sweden during the year 2010. The temperature and moisture content of the

road were monitored during the same time. The aim with the thesis was to

compare the two ways of analyses, and to find out if there is some relationship

between them and the measured environmental data. The results showed that

the base course layer and subbase decreased in stiffness during spring thaw

about 50% while the decrease in the subgrade was 20%, compared to the

backcalculated summer and autumn value. The results of the simple

calculations from the deflection basin indices were well comparable to the

backcalculation results. By comparing the backcalculated stiffness values to

the moisture content measurements it was stated that the stiffness decreased

as the moisture content increased.


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