Stabilization of dredged spoils for pavement construction in the Niger Delta, Nigeria
Natural soils underlying the East-West road are mainly clay and silt of poor quality as subgrade and subbase materials. However, dredged fine grained sandy soils stockpiled at river banks along the road as wastes may be modified for strength gain to replace the excavated natural soil during road construction. The optimum stabilization conditions of the dredged soils were determined in this study to evaluate the strength improvement for beneficial use as road construction materials in view of their large quantity and nearness to the point of use. The laboratory tests carried out on the dredged soils included particle size distribution, compaction and California Bearing Ratio. Cement stabilization was performed on the dredged spoil. Results of the particle size distribution analysis showed that about 80 % of the natural soils, but less than 2 % of the dredged spoil particles are finer than 0.075mm. The moisture content and plasticity indices of the natural soils are 37 to 57 % and 21 to 33 % respectively. They are A-7-6 to A-6-7 soils which indicate poor quality as subgrade materials. Tests on the dredged sand revealed the following range of geotechnical properties: coefficient of uniformity, 2.21 - 2.89; coefficient of gradation, 1.11 - 1.28; maximum dry density, 1.79-1.84 g/cm3; optimum moisture content, 14-15 %; and CBR of 17-20 %. To improve the engineering properties and hence suitability in pavement construction of the spoils, 4 to 7 % addition of cement for stabilization resulted in significant strength increase, with optimum results obtained on addition of 6 % cement. The natural soils constitute very poor pavement construction materials based on their index properties. They may be excavated and replaced with the dredge spoils which must be stabilized before use.
Keywords: Stabilization, dredge spoil, pavement, Niger Delta, cement