Deriving SPT N-Values from DCP Test Results: The Case of Foundation Design in a Tropical Environment

Abstract

A portable standard dynamic cone penetrometer (DCP) was used to overcome the challenge encountered in generating SPT N-values for the design of the foundation of power transmission towers traversing a tropical forest, large parts of which was inaccessible to motorized transport. However, this required the correlation of the DCP against the SPT N-values in order to be able to properly interpret the DCP test results. For this, side-by-side SPT and DCP tests were conducted at six different locations that were accessible to motorized transport, in different soil groups and under different groundwater conditions. The pair data generated was separated into four categories consisting of coarse-grained soils and fine-grained soils above ground water level and coarse-grained soils and fine-grained soils below groundwater level. Correlation equations with relatively high coefficient of determination values varying between 0.71 and 0.85 were then developed separately for each soil type under each groundwater condition. The equations were subsequently successfully applied to predict the SPT N-values for the sites that were inaccessible to motorized transport.