Geophysical and Geotechnical Investigations of Failed Sections of Road Pavements in Parts of Northcentral Nigeria

Abstract

Ernest Orji Akudo*, Kizito Ojochenemi Musa, Fabian Apeh Akpah, Jamilu Bala Ahmed II, Simeon Idowu, Mary Shaibu

Due to the incessant failure of roads in Nigeria, geophysical and geotechnical studies were conducted along Crusher-Felele Road and Natako-Felele Road in Lokoja, Northcentral Nigeria to unravel the lithology, deformational features, underlying geology, and ultimately the causes of such failures. The geophysical methods involved electrical resistivity, while the geotechnical methods include Grain size analysis, Liquid limit (LL), Plastic limit (PL), Plasticity index (PI), Linear shrinkage (LS), Compaction, and California bearing ratio (CBR) tests respectively. From the 3geoelectric parameters retrieved by interpreting the VES soundings quantitatively, 3 to 4 geoelectric layers exist (topsoil/unweathered layered, weathered layer, partially weathered layer, and fresh basement layer) accordingly. The second layer possesses a low resistivity range (1.2-88.7 Ωm), revealing weak and saturated zones capable of jeopardizing the integrity and stability of the road pavement. The grain size analysis results show that the percentage of soils passing sieves No. 10, 40, and 200 falls within the range of 55-98.3%, 21-50.6%, and 2.0-8.2% respectively. The range of the result for the LL (21.1-38.6%,), PL (6-23.1%), PI (0.0-17.1%), LS (5.0-9.3%), Optimum moisture content (11-17%), Maximum dry density (1835-1980 kg/m³), unsoaked CBR (27-62%) and soaked CBR (15-35%) reveals the properties of the soils. Based on AASHTO classification, the soils are grouped as A-2-4, A-1-b, and A-2-6 representing silty sand, or silty gravelly, and clayey sand respectively. The soils are fairly good as pavement subgrade but poor as sub-base materials.