3.2. Pavement layer materials
3.2.1. Subgrade
The subgrade soil consisted of a high plasticity clay, having a
liquid limit of 88 and a plastic index of 53 with 96.6% passing # 200
and organic content of 9.2%. It is classified as CH per Unified Soil
Classification System (USCS) or A-7-6 according to the American
Association of State Highway and Transportation Officials
(AASHTO) classification system. The clay has an optimum moisture
content of 35% and a maximum dry density of 1250 kg/m3 according
to the standard Proctor test. To simulate weak subgrade
condition (CBR ¼ 0.5), the target moisture content and dry density
of subgrade were set as 48% and 1114 kg/m3, respectively, during
construction