SLOPE STABILITY EVALUATION OF NEWLY CONSTRUCTED RAILWAY EMBANKMENT ALONG LAGOS-IBADAN RAIL LINE, NIGERIA

Abstract

This research is aimed to evaluate stability of the slope of newly constructed railway embankment along Lagos-Ibadan rail line. Soils samples were collected from KM75+500, KM90+500, KM105+500 and KM116+500 at depths ranging from 0m to 5.5m and 5.5m to 10m and taken to laboratory for tests such as particle size analysis, Atterberg limits, standard Proctor and direct shear test. The slope stability assessment was done for the high filled embankments in KM75+500, KM90+500, KM105+500 and KM116+500. Geotechnical parameters were derived from the direct shear test as inputs for slope/W software used for the slope stability assessment. The results showed that the fill materials for the embankments from 0m to 5.5m was characterized as A-2-6 (clayey soil) 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 subgrade materials from 5.5m to 10m consisting of 51% sand and 49% fines is classified as A-6 (clay soil), 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. The factor of safety of the embankments according U.S. Army Corps of Engineers shows the slope is stable at KM75+500, KM90+500 and KM105+500 has factor of safety greater than 1.3 but slope at KM116+500 is unstable as the factor of safety is less than 1.3. It was also noticed that there was increases in factor of safety with decrease in embankment height. Slope protection and soil treatment be provided KM116+500 embankments.