Characterization and Establishing Treatment Requirements for a New Railway Subgrade along Lagos-Ibadan Route, Nigeria

Abstract

Subgrade is a critical component of railway systems as it provides a stable platform for the track substructure. This paper describes an effort to characterize and evaluate subgrade treatment needs for a new railway from KM75+500 to KM116+500 along Lagos-Ibadan rail line. Samples were collected from KM75+500 KM90+500, KM105+500 and KM116+500 at depths of 0.6m, 2.5m and 4.0m and taken to laboratory for tests such as particle size analysis, Atterberg limits, standard Proctor. The results showed that the selected locations were made up of two different layers of subgrade soil. The top subgrade bed characterized as A-2-6 subgroup in AASHTO classification system comprises of 78% of sand and 17% of fine particles and is considered as average soil according to International Union of Railways specifications. The lower layer consisting of 51% sand and 49% fines is classified as A-6, with high liquid limit of 41% and plastic index of 19% at KM116+500, and is regarded as poor soil according to railway specifications that requires stabilization. Consequently, an additional stabilized subgrade layer prepared by mixing 70% clayey sand soil with 30% graded gravel needs to be provided above this layer. More so, soil reinforcement such as non-woven geotextile layer should be provided at KM116+500 having A-6 class of soil before placing the prepared subgrade.