Abstract
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
Highlights
The failure of flexible highway pavements is a common phenomenon which manifests by the development of minor potholes, road settlement, rutting and unevenness
Laboratory tests, including moisture content, Atterberg limits, particle size distribution by wet and dry sieve analyses and the density-moisture relationship using modified American Association of State Highway Officials (AASHO) compaction were performed according to procedures specified by BS 1377 (1990)
Unsoaked California Bearing Ratio (CBR) tests were performed on the natural soil samples using the optimum moisture content (OMC) obtained from the compaction test
Summary
The failure of flexible highway pavements is a common phenomenon which manifests by the development of minor potholes, road settlement, rutting and unevenness. While a number of contributory causes have been identified, such as misuse, overuse or poor construction (Ajayi 1982), the majority of the road failure in the tropics has been attributed to geotechnical factors (Adeyemi and Oyeyemi 1992). The East-West road (Fig. 1) in southern Nigeria runs across the Niger Delta, a wetland which has peculiar environment, geomorphology and soil characteristics. Engineering design of the East-West road provides for an alignment that crosses almost 60 water bodies requiring bridges and extensive removal of the natural soils due to high silt and clay content, poor geotechnical properties and very poor quality as subgrade materials
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