CHARACTERIZATION OF COHESIVE SUBGRADE SOIL FOR FLEXIBLE PAVEMENT DESIGN (IN CASE OF WEZEKA-KONSO ROAD)

Abstract

Road transport has a vital contribution for a nation development. Road has to be designed in a way that it can function in all season of the year, this could be achieved if the road is paved and the structural elements of the pavement is well designed. In general pavements are classified as rigid and flexible pavements. In rigid pavement loads are carried by the concrete itself thus the design requirement is the flexural strength of the concrete whereas in flexible pavement, the intention of the design is to reduce the deformation of the subgrade under a certain loading condition. Thus, flexible Pavement design needs proper material characterization so that failures in structural as well as functional could be mitigated. The aim of this study is characterization of cohesive subgrade soil for flexible pavement design in case of Wezeka – Konso road, Ethiopia. Identification of the Physical properties and classification of the soil was done according to AASHTO criteria. Resilient modulus was predicted from unconfined compressive strength. Additionally, a method has been developed for prediction of resilient modulus from unconfined compressive strength and index properties of soil. For both prediction models Microsoft excel was used to conduct the statistical analysis. The soils used for this study were low to medium plastic fine-grained soils. According to AASHTO soil classification system the soils were group in A-4, A-5, A-6 and A-7-5 categories. Statistical analysis shows that the relation between resilient modulus and unconfined strength was linear correlation. For this correlation the coefficient of determination value of R2 = 0.83 was obtained. For the second model which is prediction of resilient modulus from unconfined compressive strength and index properties the correlation was multilinear with coefficient of determination R 2=0.87. Due to the inclusion of index properties in the second model a better correlation was observed.