Evaluation of overconsolidation ratios from laboratory and in situ tests on Busan clay

•Overconsolidation ratio (OCR) varies depending on sample quality as well as consolidation testing methods.•Correlations between the OCR and in-situ test results lie within the limits of existing empirical formulas.•The correlations are appropriate for a site where a great majority of data is given.

The overconsolidation ratio (OCR) was determined through three different series of consolidation tests on the samples, which were retrieved using an oil-operated fixed-piston sampler at two sites in a deltaic deposit. The constant rate of strain (CRS) consolidation test and the end-of-primary (ILEOP) consolidation tests proved to be superior tests with higher quality of samples and produced close OCR values. The CRS and ILEOP tests provided OCR values close to those of the field measurements, whereas the conventional 1D consolidation (IL24) test underestimates the values. The OCR values obtained from the CRS and ILEOP tests lie between the upper and lower bounds of existing empirical formulas, whereas those from the IL24 test belong to the lower bound. Empirical formulas that were suited for both sites were newly developed through the correlations between the results of the two consolidation tests and three field tests. The empirical formulas, which have been developed based on the correlation coefficients, are appropriate for predicting the OCR values for a site where the great majority of data are given. This trend is more pronounced in the predictions obtained from the piezocone and the field vane tests than the predictions from the flat dilatometer test.