Abstract
This article presents the results of a study carried out to relate the frequency of pavement failures, the engineering indices of the subgrade materials and the underlying geology. The results show a high variability in the indices such as the liquid limit, LL, the plasticity index, PI, the maximum dry density, MDD, the optimum moisture content, OMC, compressibility and the California Bearing Ratio, CBR, between the different geologic units. Engineering indices having significant correlation with CBR (the major criteria for assessing the quality of subgrade materials), are used to develop a scheme for evaluating the materials at different failure points along the Calabar-Itu Highway in Nigeria. The evaluation shows that locations exhibiting high failure rates are underlain by shaly or marly subgrade whereas locations characterised by low failure rates are underlain by weathered basement or sandy unit as subgrade. It is recommended that maintenance and provision of drainage facilities will go a long way to reducing the rate of failure.Keywords: engineering indices, failure, road pavement, subgrade, NigeriaGlobal Journal of Geological Sciences Vol. 3(2) 2005: 99-108
Highlights
This article presents the results of a study carried out to relate the frequency of pavement failures, the engineering indices of the ? .')grade materials and the underlying geology
This study focused on the l~nderlying geology of the highway
In all cases the number of sampling points was determined by the frequenty of failure points
Summary
The study site is located In a humla tropical cl~mate The area experiences two major seasons, the wet and the dry Meteorological data for the period 1990-2000 show that the temperature varies between 21.3 and 34.3"C and 21.? a i ~ d 35.2" C for the wet and dry seasons, respectively. The study site is located In a humla tropical cl~mate The area experiences two major seasons, the wet and the dry Meteorological data for the period 1990-2000 show that the temperature varies between 21.3 and 34.3"C and 21.? The area comprises numerous lithologic sequences ranging in age from Precambrian to Tertiary. The rnajor geologic formations include the Precambrian Oban massif (gneiss, schist, granite, pegmatite etc), the Aptian-Albian Awi Sandstone (sandstone, siltstone), the Albian Mfamosing Limestone (various types of limestone), the Late AlbiarlTuronian Ekenkpon Shale (organic shale, calcerous mudstone). Coniancian #Jew Netim Marl (marl with minor calcerous siltstone beds), the Late Campanian-Maastrichtian Nkporo Shale (carbonaceous shale with rnudstone and gypsum beds), and the Tertiary Coastal Plain Sands (iravel, sand, silt, clay), as shown on Fig. 1 and In Table 1 (Ekb~ue~ne et al 1995)
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