Geophysical and Geotechnical Approaches in investigating causes of road failure along Zone 8 - Crusher Road, Lokoja, Kogi State.

Abstract

Roads are an important engineering structure that are crucial in international trade and transportation because they connect cities, states, and nations, respectively. A good number of variables, such as poor construction methods, lack of maintenance, and poor subsurface soil conditions, are major contributors to road instability globally. This study aims to investigate the causes of road failures in Lokoja and its environs, Nigeria. The study employs an integrated approach using 2D Electrical Resistivity Tomography (ERT), Very Low Frequency Electromagnetic (VLF-EM) surveys, sieve analysis, and Atterberg limit tests to investigate the causes of failure along the Zone 8-Crusher road. Eight (8) locations were examined, and soil samples were collected for analysis. The ERT and VLF-EM results revealed three distinct resistivity zones: low, intermediate, and high. The low and intermediate resistivity zones, particularly in the road’s failed sections, are likely associated with water-saturated weathered materials. Sieve analysis showed that the percentage of soil passing through sieve number 200 (0.075mm) ranged from 0.1% to 0.3%, indicating a lack of clay content, which suggests that clay was not a contributing factor to road failure in this investigated site. The Atterberg limits revealed liquid limits between 29.1% and 33.5%, plastic limits between 14.15% and 18.35%, plasticity indices between 14.95 and 15.15, and moisture content values between 8.2% and 16.8%. These results indicate low plasticity, falling within the acceptable range for soils used in road construction, thereby ruling out poor soil plasticity as a cause of the road's instability in this investigation. Therefore, the study concluded that the failures are due water water-saturated units of the topsoil and shallow weathered zone of the affected area. It may also be due to poor construction materials and a lack of road maintenance