Correlation between Dynamic Cone Penetrometer (n-Value) and Allowable Bearing Pressure of Shallow Foundation Using Model Footing

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An allowable bearing pressure is one of the most important basic parameters to be determined before the design and construction of foundations for civil engineering structures. The conventional methods of estimating this parameter is becoming relatively expensive and time consuming for small scale projects such as residential buildings. The DCP is a versatile equipment that may be applied to obtain the bearing capacity. However, currently, there are no reliable correlations between the DCP test results and the bearing capacity. This project was undertaken to develop a reliable correlation between the Dynamic Cone Penetrometer (DCP) n-value (blows/100mm) and the allowable bearing pressure qati (kN/m2) for shallow foundations using a model footing. In this work, compacted soil sample of different dry densities in a mould was loaded with a model footing until the sample yielded. On the same sample, DCP testing was performed at two locations to determine the average D- value (mm/blow). Triaxial samples were also taken for triaxial test. Results from the triaxial test were used to calculate ultimate bearing capacity using Terzaghi bearing equation. The measured DCP D-value (mm/blow) was processed into n-value (blows/100mm) which is the standard form of recording the DCP test results in the field. The results were analysed and a correlation qau=48n + 57, with a coefficient of correlation, R2=0.98 was obtained for the model footing. This correlation was similar to the correlation between the n-value and the allowable bearing pressure computed using the Terzaghi approach, except that the Model underestimated the allowable bearing pressure by a constant value of 165 kN/m2 for all values of n.
A Thesis submitted to the Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfilment of the requirements for the award of Master of Philosophy