Electrical Resistivity Tomography Survey of Some Failed Segments along Selected Major Highways in Cross River State, Southeastern Nigeria

Abstract

This study investigated some failed segments along Okuku – Okpoma and Abuochichie – Obanliku highways. Six (6) measurements employing electrical resistivity tomography (ERT) were conducted at the side of selected failed portions of the road and at the stable portions which served as controls. It was found that along Okuku – Okpoma road, the resistivity values of weak zones ranged from 25Ωm – 71Ωm at Okpoma and competent zones ranged from 840Ωm – 1376Ωm at Ugaga and 600Ω.m – 800Ωm at Ogbudu.  Along Abuochichie – Obanliku road, the resistivity values of weak zones ranged from 25Ωm – 35 Ωm at Ukwutia and 78 Ωm – 90Ωm at Bukumanya and competent zones from 828Ωm – 1021Ωm at Amunga. The results further indicated that the remote causes of road failure are as result of geologic factors such as clay/shale materials/highly weathered materials at Okpoma, Ukwutia and Bukumanya where they occurred. It was recommended that geophysical surveys should be conducted prior to the construction of roads. Also clay materials as well as highly weathered geologic materials existing beneath the pavement should be excavated and replaced with competent materials such as sandy clay, clayey sand, sandstones, granite during construction of roads before laying the asphalt especially at Okpoma, Ukwutia and Bukumanya.  Also there should be proper drainage system to prevent floods and washing of roads.