GEOPHYSICAL INVESTIGATION OF ROAD FAILURE USING ELECTRICAL RESISTIVITY IMAGING METHOD, A CASE STUDY OF UHIELE – OPOJI ROAD EDO STATE
ABSTRACT
A shallow geophysical investigation for road surface failure using 2D electrical resistivity imaging profiling was conducted to produce an approximate model of the subsurface resistivity. This study was done with the aim of revealing the horizontal and vertical geological discontinuities using electrical resistivity, an intrinsic property of all materials. Probable zones of untimely failure along the road are then investigated by variation in resistivity. Four traverses were established on the road with one parallel to the road segment. The Electrical Resistivity Imaging (ERI) Profiling involving the Wenner array 2D Imaging was adopted for the resistivity survey. The Pseudosection results revealed that the road structure is founded on a near homogeneous substratum indicating that the road is situated on a better geology than those from previous studies done in this geologic environment. The apparent resistivity values for all the profiles ranged from 273.94 Ωm – 3566.7 Ωm for profile I; 1561.2 Ωm – 4062.4 Ωm for profile II; 714.36 Ωm – 3856.4 Ωm for profile III and 700.06 Ωm – 3994.65 Ωm for profile IV. Apparent Resistivity values of Area Studied ranged from 273.94Ωm to 4062.4Ωm with an average of 2168.17Ωm which characteristically placed the studied area in a sedimentary basin with the presence of clay- sandstone inrtercalation. The low apparent resistivity values between 273.93 Ωm to 979.64 Ωm were obtained alternately with high apparent resistivity values along all the profiles investigated and were also obtained where there were major cracks, accentuated by water ingress. Geotechnically, it was inferred that highly resistive soils, usually at most times correlate with competent zones and the low resistive zones correlate to the incompetent soils. The engineering properties of soils using Weaver’s rippability rating chart (seismic velocity and hardness) of soils, showed that the low resistive soils were incompetent for engineering structures like road pavement etc. The causes of road pavement failure on the studied road was found to be majorly as a result of a combination of clayey topsoil/sub grade soils, water-logged sands due to ingress with characteristically low resistivity values and thin pavement thereby unable to withstand pressure exerted on the road.