Geotechnical and Mineralogical Evaluation of Soils Underlying a Failed Highway Section in South Eastern Nigeria

Abstract

Abstract:The Port Harcourt Enugu expressway is part of a national road grid that links parts of southern and northern Nigeria. The severe pavement failure between Umuahia and Okigwe section of the expressway covering a distance of about 30 km was investigated by geotechnical and mineralogical assessment of disturbed and undisturbed samples of the underlying soils. Also vertical electrical sounding was performed at the failed sections. Results indicate that the section is underlain by shales of the Imo Formation, and soils are composed of 27% and 74% sand and fines respectively. The Atterberg limit values are moderate to high, with liquid limit in the range of 49-54%, plasticity index 11.1-24.4% and linear shrinkage 17.86-23.57% respectively. Abrasion test results of 0.58 to 16% indicate shales of low durability. The 24 hour free swell tests results range from 33-70% implying soils of moderate to high hydro-affinity and volume change. These data corroborate the X-ray diffraction analyses results which show montmorillonite and kaolinite as the main clay minerals present in the soils. Undrained cohesion range from 9 to 54 kPa and frictional angle from 13° to 29°. High settlement amounts and field observation of intense failure correlated well with the engineering properties and the clay minerals. The soils indicate mainly MI-MH and A-7-5 soils on the USC and AASHTO classification system respectively, implying poor quality soils as subgrade materials. The engineering properties may be modified and upgraded by stabilisation. Result of the study will be useful in remedial works on the failed sections of the road and future pavement design in areas underlain by the shales.

Geotechnical, Geochemical and Mineralogical Evaluation of Mine Spoils of the Jos- Bukuru Tin Field, Central Nigeria: Implications for Utilization as Road Construction Material.

“…In investigating the potential reasons of road collapse of the Onitsha-Enugu expressway, Onuoha et al, (2014), collected and analyzed residual soil samples and concluded that the soils do not meet up with stipulated standards set by the Federal Ministry of Works and Housing. Tse and Efobo (2016) outlined potential causes for the frequent failure of the Port Harcourt -Enugu expressway to include utilization of substandard soils as the sub-grade, presence of shales of low permeability as well as the presence of signi cant amount of montmorillonite in the soil. Furthermore, Oyem et al (2020), Daramola et al (2018), identi ed poor drainage and high percentage nes and utilization of soils of high plasticity as some of the causative factors of road failure along the Sagamu-Papalanto highway in Southwestern Nigeria.…”