Integrated Approach of Geotechnical and Geophysical Investigations into Failed Segments of the Road Along Vwei (Mararaban Jama’a) - Mangu Road. North-Central Nigeria

Abstract

The aim of this study is to examine the subsurface structural disposition and provide
useful information on the soil properties with a view to proffer solution and avert
future road failure occurrences. A combined scientific approach of remote sensing,
geophysical and geotechnical investigations on the earth materials within and
around those failed segments have become a fundamental tool to discovering the
factors responsible for the insistent problems. Vertical Electrical Soundings (VES)
probe of the failed portions gave three (3) to four (4) layered earth interpreted to
contain clayey-sand and loose saturated sand units at the upper portion, highly
saturated weathered/fractured basement and fresh basement at the lower portion.
The resistivity values for the top soil is 139Ωm - 366Ωm, weathered layer is 20Ωm-
101Ωm, weathered/fractured layer is 30Ωm - 473Ωm and fresh basement is 284Ωm
- ∞Ωm. The thickness of the top soil is 0.6m - 1.9m, weathered layer is 5.4m to
39.1m, weathered/fractured layer is 2.0m - 25.8m and fresh basement 11.1m -
39.4m respectively. CBR result range from 23.40 – 36.40%, indicating percentage
reduction in strength with wetness of 43.7% - 50.8%. Liquid limit, linear shrinkage
and plastic limit index gave values in the range of 28.0 - 47.5%, 3.6 - 10.7%, 11.4 -
18.9% respectively. This study implies that integrated structural geology,
geophysical and geotechnical investigations offer very useful approach for
characterizing near surface earth and thus can help in preparation before
engineering structures are found on same.