EFFECT OF VARIATION IN MOISTURE CONTENT ON THE DURABILITY OF SUBGRADE LAYER

The subgrade soil always suffers from variation in the level of moisture due to many factors such as capillary action, precipitation, flood, and change in groundwater table. So, it''s very important for the engineer to understand clearly the nature of relationship between the subgrade strength and variation in moisture. The main objective of this study is to investigate the changing in the strength and durability of subgrade soil due to the variation in water content. The natural samples tested with three percentages of moisture contents (11.5%, 13.5%, and 15.5%).Physical and chemical tests are carried out on the natural soil samples brought from Al-Sader city. The soil classified as lean clay with accordance to Unified Soil Classification System (USCS) while classified as (A-7-6) according to (AASHTO) classification system. After (28 days) period of leaching for the natural samples with different moisture contents and under surcharge load of (10 Ibs.) the results indicate that, the samples at the dry side give higher resistance to leaching strain as compared to the other samples. With the increasing of hydraulic gradient; the strength of soil will decrease.