Geophysical and Geotechnical Investigation, and Lime Stabilizing Effect on Subgrade Failure Around a Section of Lagos-Abeokuta Highway

Abstract

An electrical resistivity survey and geotechnical investigations were employed to examine the factors responsible for incessant roadway failure along sections of the Lagos-Abeokuta highway in Southwestern Nigeria. A study on the efficacy of lime as a stabilizing agent on failed subgrade soil was also conducted. Electrical resistivity imaging and laboratory geotechnical tests with the aid of grain size analysis, Atterberg’s limits, the standard proctor compaction test, the CBR (unsoaked and soaked), and the compression test (UCS) were carried out for this study. The 2D resistivity images reveal incompetent subgrade layers with resistivity values ranging between 12– 88.3 Ω.m, and values ranging between 21.5 and 127.3 Ω.m at a depth of approximately 2 m for the VES investigation. The laboratory geotechnical tests’ results along the failed segments also reveal poor subgrade soils which are composed of clay, clayey sand, and sandy clay; with plasticity indices ranging between 29.4 and 31.5, and average values of 74.5 KN/m2 and 1.69 g/cm3 for the UCS and maximum density, respectively. However, with lime admixture to the soil samples in 2%, 4%, 6%, 8%, and 10% proportions, there was a progressive improvement in the shear strength of the clayey soil samples, owing to the reduction in the plasticity and increase in the MDD and UCS.