GEOPHYSICAL INVESTIGATION INTO THE REMOTE CAUSES OF ROAD FAILURE ALONG FARIN GADA- ZABOLO ROAD, JOS, NORTH CENTRAL

Abstract

Detailed geophysical investigation for road failure using Schlumberger and the Werner Array
geophysical investigation was carried out. These investigations were done with the aim of
revealing the horizontal and the vertical geological discontinuities using their electrical resistivity,
intrinsic property of the materials, probable zones of untimely failure along the road. The VES
readings of the Schlumberger array method showed that the failed sections of the road had low
resistivity values that ranges from 19.3Ωm (ohm-meter) to 80.5Ωm (ohm-meter) while the unfailed
sections of the road had resistivity values that ranged from 210.5Ωm (ohm-meter) to 491.2 Ωm
(ohm-meter). The failed sections of the road from interpretation had high content of clay in them
which is responsible for the failure while the unfailed section is made up of sand mainly. For the
Werner array survey, investigation revealed that only the soils around Horizontal Electrical profile
2 (HEP2) were competent because of their high resistivity ranges from 343.06Ωm (ohm-meter) to
2092.30Ωm(ohm-meter) while soils in profiles HEP1 and HEP3 were made up of soils that are
incompetent because of their relative low resistivity values ranging from 40.80Ωm(ohm-meter) to
543.80Ωm(ohm-meter). VES readings obtained at locations 9,11,13,14 and 15 had soils that were
competent because of their high resistivity values that ranged from19.3Ωm (ohm-meter) to
197.4Ωm (ohm-meter) and were collected from the undamaged sections of the road while locations
1,2,3,4,5,6,7,8,10,12,16,17,18,19,20,21,22,23,24 and 25 had low resistivity values that ranged
from 205.3Ωm(ohm-meter) to 1049.8Ωm(ohm-meter) and were collected from the damaged
sections of the road. The causes of the road failure in the study area were found mainly to be as a
result of clayey top soil/ sub grade soils due to the nature of the geology of the area which is mainly
granitic in nature that contain a lot of feldspars which upon weathering gives rise to clay (kaolin).
The continuous decomposition into clay (kaolin), poses a great threat to the road due to expansion and contraction of the clay. The coarse grained type of the Biotite Granites are more resistant to
weathering and have lesser amount of feldspars in them and upon weathering gives birth to
laterites, gravels and sand which have high resistivity values as seen in the undamaged sections of
the road while the medium to fined grain type of Biotite Granites have a very high amount of
feldspar content in them and upon weathering gives rise to clay which have low resistivity values
as seen in the damaged sections of the road. The presence of thin pavements which are unable to
withstand pressure exerted on the road was also another cause of the road failure. Hence, the result
of this research will form the tools for which the causes of the road failure can be identified and
how they can be remedied within the study area using appropriate measures.