Comparison between USCS and USDA shows that while 10% each of CL samples as per USCS classified as Silty Clay (SIC) and Clay Loam (CL), the remaining 80% classified as Clay (C) based on USDA. The results also show that whereas 100% of the Lean Clay (CL) samples as per USCS, classified as Clay of Intermediate Plasticity (CI) in BSCS, 67% and 33% of the CL samples classified as A-7-5 and A-6 respectively in AASHTO. The analysis shows that 80% of samples that were classified as Fat Clay (CH) on the basis of USCS, classified as Clay of High Plasticity (CH) in BSCS, while 20% classified as Clay of Very High Plasticity (CV). Correlation between the classification schemes was determined by analysing the consistency with which sample groups in the BSCS, AASHTO and USDA matched the corresponding sample group in the USCS.

Generally, the upper sections of the boreholes (< 10m depth) were dominated by fine (clay and silt) sediments, while the proportion of coarser (sand and gravel) geomaterials increased with depth. The soil samples were also classified according to procedures stipulated by the other 3 classification schemes. From the results, 6 samples each were of the Fat Clay (CH) and Lean Clay (CL) categories, 10 samples were classified as Clayey (SC) or Silty (SM) Sand, while 4 samples each were Poorly Graded Sand with Silt (SP-SM) and Poorly Graded Sand (SP) respectively based on USCS. The Unified Soil Classification System (USCS), British Soil Classification System (BSCS), American Association of State Highway and Transportation Officials (AASHTO) and the United State Department of Agriculture (USDA) classification systems were used in the analysis. In this study, laboratory testing of thirty disturbed soil samples obtained from eight boreholes in the project area was carried out to classify the soils and determine the correlation between the classification schemes.

Aashto a1 a2 a3 soil