Extracting some soil parameters and estimating elastic settlements from Direct shear box data for a granular C- Ø soil

Abstract

Direct shear box tests were carried out on some soil samples obtained from some locations around Uyo metropolis in Akwa-Ibom State, Southeastern Nigeria. The dominant geology is the Coastal Plain Sands. From the test results, the C-Ø properties of the soils were determined. These values were used to compute ultimate and allowable bearing capacities for the soil samples. Elastic, and shear modulus parameters were computed for the different shear values readings for each vertical loading scheme. Poisson ratio was also computed for the same loading scheme applying the elastic relationship between shear modulus and elastic modulus. These parameters were used to compute elastic settlement using the classical elastic theory equation. Two other modified equations of the elastic theory equation and a consolidation equation was also used to compute immediate and consolidation settlements respectively. The values of immediate settlement obtained for the classical elastic equation is less than those computed by the other two modified equations. This is attributed to the fact that the other two equations assumed a constant value of Poisson ratio for the different imposed loads for which computations were made. For the allowable load of 138.54 kPa the classical elastic theory gave an immediate settlement value of 1.02 cm; the other two modified forms of the theory gave values of 2.94 cm and 4.0 cm. Elastic modulus and Poisson ratio obtained from the Direct shear test for the load are 5662.86 kPa and 0.49. These values were used in the elastic equation. The same value of 5662.86 kPa was used in the other two modified elastic formulas, but Poisson ratio values of 0.15 and 0.2 were assumed for all loads. Direct shear box test provides a convenient, but plausible means of determining parameters required to compute immediate settlement for the type of soil investigated.