Journal of Earth Sciences and Geotechnical Engineering
An Assessment of the Geotechnical Aspects of Njaba River Sediments in the Eastern Niger Delta Basin, Southeastern Nigeria
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Abstract
Some geotechnical characteristics of sediments in the Njaba River watershed were assessed to highlight their potentials as good construction materials. The studied sections at the river bank is comprised from top to bottom lateritic top soil, fine-medium grained yellowish sand, coarse grained whitish sand and gravel. This succession displays a fining-upward sequence typical of point bar deposits. The obtained values of Plasticity Index (PI), Plastic and Liquid Limits (PL and LL) using standard equipment were 7.10, 16.90 and 24.00 % respectively. The observed low Plasticity Index is indicative of the absence of very active clays such as montmorrilonite that cause damages to structures as a result of slaking. Results of Direct Shear Strength, Optimum Moisture Content, Optimum Density, Bulk Density and Dry Density of analyzed laterite samples were 101.20KN/m2, 12.00 %, 2.11, 2.24 and 1.97 Mg/m3 respectively, while the California Bearing Ratio (CBR) for soaked and unsoaked laterite samples were 22 and 72 % respectively. The calculated values of Coefficient of Curvature and Coefficient of Uniformity for the laterite, fine-medium grained sand, coarse grained sand and gravelly samples indicate that the sediments are fairly well-graded. The mean values of bulk density, specific gravity, water of absorption, Average Crushing Value (ACV) and Los Angeles Average Value (LAAV) for the gravel samples were 2.31Mg/m3, 1.95, 1.88, 25.53 and 24.90 % respectively. Although the bulk density and LAAV values of gravel samples in the study area did not conform to the BS (1973) Standard, the specific gravity, water of absorption and ACV values were in conformity to the standard. The bulk density and LAAV values indicate that the Njaba River gravels are too soft to be used as wearing surfaces (aggregates) for highway pavements. However, the gravel can be used for the construction of civil structures such as buildings and culverts. The laterites are suitable for use as base and sub-base courses for road construction based on their CBR, direct shear and bulk density values. The sands can be used to make blocks and for the construction of culverts, drainage facilities and buildings.
