Earth Sciences Malaysia (ESMY) 4(1) (2020) 51-60 Quick Response Code Access this article online Website: www.earthsciencesmalaysia.com DOI: 10.26480/esmy.01.2020.51.60 Cite the Article: Olumuyiwa Olusola Falowo, Adekunle Aliu (2020). Geoengineering Investigation Of An Erosion Induced Highway Structural Failure Along Ifon – Benin Highway, Southwestern Nigeria. Earth Sciences Malaysia, 4(1): 51-60. ISSN: 2521-5035 (Print) ISSN: 2521-5043 (Online) CODEN: ESMACU RESEARCH ARTICLE Earth Sciences Malaysia (ESMY) DOI: http://doi.org/10.26480/esmy.01.2020.51.60 GEOENGINEERING INVESTIGATION OF AN EROSION INDUCED HIGHWAY STRUCTURAL FAILURE ALONG IFON – BENIN HIGHWAY, SOUTHWESTERN NIGERIA Olumuyiwa Olusola Falowo*, Adekunle Aliu Department of Civil Engineering Technology, Faculty of Engineering Technology, Rufus Giwa Polytechnic, P.M.B 1019, Owo, Ondo State, Nigeria *Corresponding Author Email: oluwanifemi.adeboye@yahoo.com This is an open access article distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ARTICLE DETAILS ABSTRACT Article History: Received 12 June 2020 Accepted 15 July 2020 Available online 9 September 2020 Road infrastructural is one of the most important economic indices for development of a country. Therefore in-situ cone penetration test and laboratory soil analysis were performed at two failed segments along Ifon- Benin highway, with the aim of determining cause(s) and extent of the failure. The cone penetration test was carried out to a depth of about 20 m with a lateral spacing of 20 m along the roadway. The laboratory tests conducted were grain size analysis, Atterberg limit test, compaction test, California Bearing Ratio, and undrained unconfined triaxial test. The results revealed that all the soil parameters fell short of the federal ministry of works and housing specification of Nigeria, with plasticity index (>20%), % fines (>35%), CBR values (<80%) recommended, angle of friction and cohesion are less than minimum standard of 30° and 50 Kpa respectively. The CPT revealed predominant sandy silt to clayey silt topsoil and clay substratum with compressive strength of 20 – 40 KN/m 2 . The water level is higher than 3 m, consequently far below the road foundation baseline. Findings showed that the upper 6 m of the failed segments has been seriously affected by erosion and flooding. Subsequently the process resulted into excessive settlement of the silt/clayey- subgrade soil underneath the pavement structure. This makes the highway to settle largely under traffic load. In addition, incessant heavy flooding around the embankment/shoulder of the highway might have induced the failure, leading to looseness, and less-cohesion of the layers which invariably reduces subgrade support and weakens various pavement layers. KEYWORDS Bearing capacity, Erosion, Geologic section, Highway, Penetrative resistance. 1. INTRODUCTION Road transportation is an important element in the physical development of any society as it controls the direction and extent of development (Daramola et al., 2018). Necessity of highway infrastructure development has been one of the most important indices in measuring growth of nation’s economy. Consequently it must be given all attention it deserves (Falowo and Dahunsi, 2020). A country’s economic status depends upon how well served the country is, by its roads, railways, air ports, ports, pipelines and shipping (Obaje, 2017; Ilori, 2015; Ajani, 2006; Aghamelu and Okogbue, 2011). The rate at which a country’s economy grows is very closely linked to the rate at which the transport sector grows (Kadyali and Lal, 2008). Transport minimizes the time for the movement of people and goods, thus transport gives utility to economic activities and facilitates quick economic development. Road structure consists of number of layers (subgrade, subbase, base course, wearing surface), each of which has a particular function. The wearing surface of a modern road consists bituminous bound aggregate or a concrete slab, although a bituminous surfacing may overlie a concrete base. A concrete slab distributes the load that the road has to carry, whereas in a bituminous road, the load primarily is distributed by the base beneath. The base and sub-base are below the surface course and generally made of granular material, although in heavy-duty roads, the base may be treated with cement. The subgrade refers to the soil immediately beneath the sub-base. However much the load is distributed by the layers above, the subgrade has to carry the load of the road structure plus that of the traffic. Consequently, the top of the subgrade may have to be strengthened by compaction or stabilization (Hartley, 1974; Black and Lister, 1978). The strength of the subgrade, however, does not remain the same throughout its life. Changes in its strength are brought about by changes in its moisture content, by repeated wheel loading, and in some parts of the world by frost action. Although the soil in the subgrade exists above the water table and beneath a sealed surface, this does not stop the ingress of water. As a consequence, partially saturated or saturated conditions can exist in the soil. Also, road pavements are constructed at a level where the subgrade is affected by wetting and drying, which may lead to swelling and shrinkage, respectively, if the subgrade consists of expansive clay (US Army Corps of Engineer, 2004). The highway embankment is also important element of pavement structure must also have sufficient bearing capacity to prevent foundation failure and also be capable of preventing excess settlements due to the imposed load (FWHA, 2006; Hadjigeorgiou et al., 2006). It should be