Abstract
The high global numbers of road accidents due to bad roads and the failure of other engineering structures have necessitated this study, particularly as road transport accounts for a higher percentage of cargo movement in African countries. The geophysical investigation was carried out on six failed and two stable sections along the Ibadan-Iwo-Osogbo highway to examine the geological factors responsible for highway failure in the area. A Landsat ETM+ (Enhanced Thematic Mapper Plus) imagery of the study area and its environs was acquired and processed for lineaments analyses. Magnetic, Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity methods involving Schlumberger Vertical Electrical Sounding (VES) and 2-D imaging using a dipole- dipole array were utilized. Lineaments were identified across failed localities. Lateral magnetic variations in the near-surface geological materials characterized the study area. The 2-D VLF-EM models generated showed conductive zones corresponding to fractured zones of conductive clay materials within the basement rocks. Subgrade soils below the highway pavement along the failed sections are typical of incompetent clayey and sandy clay/clayey sand formations with resistivity values between 20–475 Ω∙m. In comparison, the subgrade soil beneath the stable sections has moderate to high resistivity values of 196–616 Ω∙m. 2-D resistivity structures across the failed segments identified low resistivity water-absorbing clay and lithological contacts. Water absorbing, clay enriched subgrade soils and the identified near-surface linear conductive features are the major geologic factors, and poor drainage network resulted in the highway failure. Remote sensing and geophysical investigations of the geological sequence and structures underlying the highway should be carried out before construction to effectively complement the routine geotechnical studies to ensure the sustainability of road nfrastructure.
Highlights
Road transport is the most commonly used means of transportation in Africa
Site investigation using geophysical methods is more beneficial since it provides detailed information about the subsurface, which in turn determines how feasible an area would be in terms of the erection of structures that will stand the test of time (Oluwafemi 2012)
Land satellite imagery and integrated geophysical methods have been used in establishing that geological factors have contributed to the continuous failure of the highway
Summary
Road transport is the most commonly used means of transportation in Africa. the rate at which these roads, including highways, have failed has increased tremendously in recent times, and this calls for immediate attention. Remote sensing and integrated geophysical data will provide an effective way of assessing the causes of the continuous failure of the road transportation infrastructure network in the Africa region. This is because these developing countries have lost precious infrastructure worth billions of dollars through road pavement failures. This research attempts to find out the cause(s) of persistent pavement failure along Ibadan-Iwo-Osogbo Highway by integrating satellite imagery of the study area and its environs with geophysical investigation This serves as a post-construction study to establish a geological basis and any other reasons for the instability of the road pavement and proffering lasting remediation measures
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