4.3. Permanent deformation in base and subgrade
As previously mentioned, the customized potentiometer was
installed at the mid-height of base layer to measure the compressive
strain. It is assumed here that the compressive strain at the
mid-height represents the mean compressive strain of the whole
layer. As such, the overall deformation of the entire base layer was
determined by multiplying the measured compressive strain by the
thickness of base layer. In the subgrade layer, a customized LVDT
was mounted on a steel rod, which has an end fixed to the bottom
of the steel box. Therefore, the deformation measured by the LVDT
is the overall deformation of the entire subgrade layer. Fig. 5a and b
illustrates the development of base and subgrade permanent
deformation with number of EASLs. As can be seen from the figures,
for the control section (section 4), the subgrade layer makes more
significant contribution to the total permanent deformation, when
compared to the base layer. The use of geosynthetics resulted in
reducing the permanent deformations in both the base and subgrade
layers (sections 2, 3, and 5). However, when the geosynthetic
is placed at the baseesubgrade interface, significant reduction of
permanent deformation occurred in subgrade layer while only
small reduction of permanent deformation was observed in base
layer (section 3 and 5). This means that the geosynthetic at the