SPT-CPT Correlation in Southeast Queensland, Australia

SPT-CPT Correlation in Southeast Queensland, Australia

Among the most popular in situ investigation techniques for identifying subsurface strata, cone penetrometer testing (CPT) and standard penetrometer testing (SPT) are employed in geotechnical engineering. In fact, both tests are adopted to correlate a wide range of geotechnical parameters in various design applications. The cost associated with conducting both in situ tests at the same locations often results in one method being chosen over the other. Hence, engineers have to corelate one of the tests’ parameters into the other test using empirical correlation in translating SPT blow counts (SPT-N) into CPT cone tip resistance (CPT-qc). However, disadvantages of this in situ test are that it does not directly quantify geotechnical parameters but uses correlations which are significantly influenced by soil properties. Also, many of correlations do not provide sufficient background on the statistical approach. This study investigates the conformity of the empirical correlations against local SPT-CPT correlation for different soil occurrences in Southeast Queensland (SEQ), adopting a linear regression model to validate the degree of the relationship. Seven soil groups were classified in SEQ, comprising cohesionless and cohesive soil. The results of the SEQ samples showed a strong liner relationship (r = 0.69 – 0.89) with at least 50% of data points coinciding with the regression line (R2 = 0.48 – 0.80). It follows that for some soil groups, the published correlation agrees well with the SEQ study, while others did not.

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