Abstract
Tropical red soils which occur in the dry flatlands and plains of the eastern Niger Delta Nigeria were evaluated using combined conventional engineering geological investigation with major oxide geochemistry to determine their properties and evaluate their engineering performance in road construction. Laboratory test results indicate that the brownish materials are uniformly graded, silty clayey sandy soils. The silica to sesquoxide ratio values of 3 to 4.37 indicate that they are non-lateritic tropically weathered soils. The average values of the specific gravity, liquid limit, plasticity index and shrinkage limits are 2.67, 37%, 10% and 7.6% respectively. They are soils of low to medium plasticity. The unsoaked and soaked CBR values range from 14-38% and 3-9% respectively whereas the average undrained shear strength is 172kN/m2. Maximum dry density and optimum moisture content values fall between 1680 to 1880kN/m2 and 13-16% respectively. Generally the soils classify as A-7-6 to A-2-4 subgroups of the AASHO classification. The overall implication of these composite engineering properties is that the non-lateritic soils rate as poor to fair subgrade materials.
Highlights
The Niger Delta wetland area in Nigeria consists of three geomorphologic zones including the coastal or Lower delta zone, Transition or Mangrove zone and the Upper deltaic plain or freshwater zone
The freshwater zone consists of dry flatlands and plains (Akpokodje 1989 and Teme 2002) and its subsurface soil profile consists of a top lateritic clay layer underlain by silty clays and sands which are in turn succeeded by poorly graded sand and gravel
Lateritic soils which give optimum moisture content (OMC) between 8-10% and above 10% are rated by Philips (1952) as average to poor respectively for use under bituminous surfacing
Summary
The Niger Delta wetland area in Nigeria consists of three geomorphologic zones including the coastal or Lower delta zone, Transition or Mangrove zone and the Upper deltaic plain or freshwater zone. The coastal and mangrove zones contain nearly 70% of the numerous marshes and back swamps that occupy as much as 50% by area of the entire delta region. The relatively less “wet” conditions in the freshwater zone coincide with the occurrence of lateritic or tropical red solids These deltaic lateritic soils differ markedly from the other lateritic soils because of some mode of formation related peculiarities (Omotosho, 2015). Alabo et al (1984) studied these soils in Port Harcourt area and its environs which belong to the freshwater zone They referred to the soils as ‘deltaic red soils’ on the basis of their colour, one of the several identifying criteria for laterites and lateritic soils. Due to the abundance of these soils and ready availability, they have been widely used in the construction of foundations, roads, airfields, low-cost housing, jgg.ccsenet.org
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