Mineralogical, geochemical and geotechnical analyses were carried out to evaluate the contributions of geological and geotechnical properties of subgrade soils to the incidence of failure of the Ipele–Isua road, south-western Nigeria. Field observations showed that the road is in a very poor state of disrepair as major portions of the road alignment have failed. The road alignment is underlain in places by Quartz Schist, Banded Gneiss and Granite Gneiss. The results of the laboratory tests revealed that the natural moisture content ranges from 6.5 to 23.3%, liquid limit from 20.1 to 55.1%, plasticity index 5.2 to 22.2%. The grain size analysis showed that the amount of fines ranges from 13 to 60.8%. Others are linear shrinkage between 2.9 and 11%, free swell between − 16.67 and 41.94%, maximum dry density from 1520 to 1792.1 kg/m³ and CBR between 2 and 17%. The specific gravity ranges from 2.51 to 2.63. The major clay minerals present are kaolinite and dickite with dominance in 50% of the samples. Major oxides present are SiO₂, Al₂O₃, Fe₂O₃, K₂O. Na₂O, MgO and CaO are generally less than 1%. Based on AASHTO classification, 19% of the samples are classified as A-2-4, 33% classified as A-2-6 while 44% classified as A-7. Dominance of low California bearing ratio, low maximum dry density, high linear shrinkage and A-7 soil group expectedly contributed to poor geotechnical properties of the subgrade. Absence of drainage is suspected to have worsened the failure as exhibited on the road.

中文翻译：

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尼日利亚西南部主要公路的过早故障：以伊佩勒伊苏阿高速公路为例

进行了矿物学，地球化学和岩土工程分析，以评估路基土壤的地质和岩土属性对尼日利亚西南部Ipele-Isua公路破坏的发生率的贡献。实地观察表明，由于道路调整的主要部分失败，道路处于非常糟糕的失修状态。Quartz Schist，Banded Gneiss和Granite Gneiss铺设了道路。实验室测试结果显示，天然水分含量为6.5至23.3％，液体极限为20.1至55.1％，可塑性指数为5.2至22.2％。粒度分析表明，细粉的量为13-60.8％。其他是线性收缩率在2.9％至11％之间，自由膨胀率在− 16.67至41.94％之间，最大干密度在1520至1792.1 kg / m之间³和CBR在2％和17％之间。比重为2.51至2.63。目前存在的主要粘土矿物是高岭石和重沸石，占样本的50％。主要氧化物本为SiO ₂，AL ₂ ö ₃，铁₂ ö ₃，K ₂ O.的Na ₂O，MgO和CaO通常小于1％。根据AASHTO分类，有19％的样品被分类为A-2-4，33％的样品被分类为A-2-6，而44％的样品被分类为A-7。较低的加利福尼亚承载比，较低的最大干密度，较高的线性收缩率和A-7土层的优势预计会导致路基的岩土性能较差。怀疑没有排水会加剧道路上的故障。