The Effect of Soaking Period on The Strength of Sub-Base Material: In The Case of Dimtu-Bilate Military Training Center Road Project

Abstract

The subbase is an unbound material that helps reduce traffic stresses to acceptable levels in the subgrade. The aim of this research is to investigate the effect of soaking period on the strength of sub-base material. To achieve these objectives the sub-base material was sampled from two borrow sites located in Southern Nations, Nationalities and peoples region, Sodo Junction (Dimtu) – Bilate Military Training Center Road Project Ethiopia. The laboratory tests were conducted to determine the physical and mechanical properties of the sub-base material. The CBR tests were performed on samples for different soaking periods (0, 1, 2, 3, 4, 5,6 and 7 days). The results showed that the sub-base material is classified as well-graded gravel (GM) and poorly graded gravel with clay and sand (GC-GP) according to the Unified Soil Classification System (USCS), while A-2-4 with respect to AASHTO soil classification system. The maximum dry density and optimum moisture content were 1.93 g/cm3 by 12.80% for BS-1 and 1.89 g/cm3 by 14.50% for BS-2. The unsoaked CBR value was 61%, while the CBR values after 7 days of soaking were 55% for BS 1 and the unsoacked CBR value for BS-2 was 46% while the CBR values after 7 days of soaking were 30%. The findings indicate that the CBR value decreased as the soaking period increased specially for plastic soils than non-plastic soil, implying a reduction in the strength of the sub-base material. Therefore, it is recommended to consider the effect of soaking period when designing sub-base layers to ensure the long-term performance of the pavement structure.