Recurrent Flood-Washed Flexible Pavement Failures in Wilberforce Island, Nigeria: Proposed Solutions

Apart from flooding homes and making several persons homeless for weeks, the 2022 Flood in Nigeria destroyed the only major road into the Wilberforce Islands, just as it occurred in 2012. The three major damaged portions of this lone road that connects the State University and the Bayelsa Cargo Airport with the State Capital in Yenagoa were at Coordinates N4o 58’ 48”, 6o 12’0”E (Airport Junction), N4o 59’ 9”, 6o 8’ 48”E about 4.5 km from the University town and at N4o 59’ 26”, 6o 7’ 51” close to Ogobiri, where some staff and students also reside. All the failures had similar pattern and root cause of piping through the heaped sand that serves as the sub-grade and base course to the asphalt-finished flexible pavement. The critical locations are flood plains and zone in the predominantly below sea level mangrove region of the Delta. Previous geophysical survey studies, using Abem Terrameter (SAS 1000) for the Vertical Electrical Sounding (VES) by Schlumberger configuration was carried out. Maximum current electrodes spread of 1000m and and potential electrodes of 40.0m were adopted. The resistivity data obtained was interpreted using computer software programme, RESIT. The three flood-washed locations were within the five VES stations investigated in order to evaluate the depth affected. It was observed that the depth below the subsoil, 4.0m to about 30.0m, has remarkable low resistivity between 18 Ωm and 154.2 Ωm, Within this depth, lies the section mainly affected by the flood-washed. The results from the geo-electric layers and lithology showed that the plains have rich deposit of silts and Clay beneath the sediments transported during flooding and serving as a seal that prevents seepage into the aquifers in the plain. Practical and permanent solution to this cyclic pavement failure requires grade separated rigid pavements (bridges or flyovers) in the identified sections, if necessary. Diversion of the flood water into the aquifer beneath the alluvial Clayey soil, as a way of conserving fresh water is also necessary in the study area. The modification of the pavement design around the frequently breached locations, using the information from this research about the depth of Clay and fine Sand along this road, should also be given consideration