Journal of Earth Sciences and Geotechnical Engineering

The Influence of Soil Mineralogy on the Failure of the A123 Ilorin – Lokoja highway, Nigeria

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• Abstract

  
  

  Due to incessant highway failures, the mineralogy, geological and geotechnical properties and behavior of the subgrades were investigated. Methods involved field sampling, geotechnical laboratory and x-ray diffraction analysis. Results show a complex mineral assemblage consisting of varying proportions of several clay and non-clay minerals with a general prevalence in kaolinite (0.9 – 57.3%) and quartz (3.4 - 87.3%). One-fifth of the soils contain 2:1 expansive clay minerals of the smectite (Na-montmorillonite) group, with at least 20% of each sample recording 10 – 30% of the expansive clay minerals in the failed highway sections. The maximum range of the 2:1 expansive clay was 14.0 – 22.0cts with a mean range of 7.2 – 9.7cts and standard deviation varying from 7.0 to 7.9 across the different rock terrains. The 2:1 expansive clay mineral of smectite group depicted weak and low bearing strength characteristics (CBR range of 1. 09–3.0%) natural bulk density of 720 kg/m3 – 1010kg/m3, maximum dry density (MDD) ranging from 670 kg/m3 – 890kg/m3 and optimum moisture content (OMC) varying from 7.75 – 18.75% and classifying as A6/7 AASHTO materials. Other clay minerals were identified and XRD analysis with mineralogical intensities range from 10cts – >15cts showed CBR strength as high as 12.28% and classifying as A-4 (silts) and A-2 AASHTO materials in stable highway sections.

  
  

  Keywords: Clay minerals, Engineering properties, composite and permeable pavement.