GEOLOGICAL AND GEOTECHNICAL INVESTIGATION OF ROAD FAILURES IN NIGERIA: A CASE STUDY OF PARTS OF IMO- ABIA STATES, SOUTHEASTERN NIGERIA

Abstract

Bad conditions of roads and their negative effects on environment and National development necessitated this research on road failures in parts of Imo and Abia States, Southeastern Nigeria, using integrated geological mapping, electrical resistivity measurements and geotechnical analyses, to determine geological factors causing road failures in these areas and proffer sustainable solutions to them. Results reveal the most complex deformations occurred in the Asu River Groups, Eze-Aku, Bende Ameki and Imo Shale formations. These formations consist of alternating sequences of incompetent rocks like clays, shales and mudstones, with resistivity range of 3.5 Ωm-22.0 Ωm, occurring down to depths of 50.0 m in places. The in-situ moisture content ranges from 5.0-21.5 %, with mean of 13.25 %. Sieve analysis shows the lithology consists average fines >80%, sand 15%, gravel<3%, are poorly graded and texturally immature. The drainage system is poor; the water table is shallow with low permeability, causing periodic swelling and shrinkage, which aggravate environmental deformation and road failure. In the northern parts of the area, the NNE-SSW trending faults and folded Okigwe-Abakaliki escarpment zone increases frequency of road failures. In the southern parts Aba, Owerri, Umuahia and Orlu failures are mainly due to unconsolidation, topography/slope instability, erosion and poor engineering practice. For effective performance and durability, pre-construction site investigation and materials standardization involving geologists, engineers and government is necessary. Improvement by surface / subsurface pumping techniques, suitable drainage systems, excavation, filling and stabilization with appropriate geo-textiles are suggested.