No abstract

Sediment deposition has increased at a meander section of Mbaa river resulting in a drastic reduction of water storage. It has necessitated calls for sand-mining or periodic dredging which could have far-reaching impacts on the aquatic ecosystem, depending on the texture and chemical compositions of the sediment. Therefore, surficial sediments samples were analyzed for textural characteristics, mineralogy and chemical compositions. Grain sizes and mineralogical analysis showed that the sediments were moderately sorted, mesokurtic, near symmetrical - slightly positive skewed, subangular – subrounded medium grained-sands, and consist of about 2.5% feldspar, 2.7% rock fragments, 5.4% hematite and 89% quartz. Mean TOC and pH were 0.39 wt% and 6.48 respectively. Atomic Absorption Spectrophotometer (AAS) analysis results showed general low concentrations of metal elements: mean values of alkali/alkali earth metals ranged from 1.33 - 3.72ppm, transition metals ranged from 0.12 - 23.07ppm; while Pb (a poor metal) was not detected. General low concentrations of metals and TOC; and non-detection of Pb suggest lack of mineralization zones and minimal anthropogenic impacts in the upstream areas.  Textural and chemical characteristics and moderate energy of river water flow suggest that human resuspension of the sediment deposit will result in minimal lateral dispersion of sediment in the water column, except during heavy rainfall. Therefore, periodic dredging or sand mining will cause minimal impact on the aquatic ecosystem, especially in the distant downstream areas, whereas within the meander section and nearby areas of the river, it is expected that there will be a significant change in water quality parameters due to the increase in the concentrations of suspended and dissolved compounds.

The incessant failed spots in the road pavement along the 27.61km Mbaitolu-Ikeduru-Ahiara Mbaise highway in Imo state, southeastern Nigeria, has necessitated this geotechnical study to evaluate the impact of the subgrade material quality on the road pavement failure. The study entailed both physical and geological assessment of the predominantly sandy to clayey silt Benin Formation underlying the area, as well as field and laboratory engineering tests on the subgrade materials underlying the road alignment. The engineering tests carried out included the grain size distribution, specific gravity, natural moisture content, Atterberg (liquid and plastic) limits, compaction (to determine maximum dry density and optimum moisture content), California bearing ratio (CBR), and shear strength (to determine cohesion and angle of internal friction). The engineering test results indicate that the natural moisture content values range between 10.4 and 18.9%, liquid limit between 36.0 and 48.6%, plastic limit ranges from 26.1 to 31.6, with corresponding plasticity index values that range from 9.2 to 17.0%. The grain size distribution test results connote the predominance of sand, with number of fines-sized particles that ranges from 22 to 38% and amount coarse to medium sand-sized particles ranging from 62 to 78%.Maximum dry density ranges from 1.29to 1.93 kg/m3. (CBR) ranges from 3.7 and 91.9%. Specific gravity ranges between 2.56and 2.61, while cohesion and angle of internal friction range from 39 to 42 kPa, and 14 to 20°, respectively. Some failed portion especially in Inyishi area were likely due to moisture fluctuation in the subgrade due to closeness of the water table. Proper compaction, chemical stabilization, and appropriate drainage would likely boost the efficiency of the subgrade material and the durability of the road pavement.