CPT Correlations for Estimating Undrained Shear Strength of Marine Clay Offshore East Africa-Paper

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The study develops site-specific cone penetration test (CPT) correlations for estimating the undrained shear strength of deepwater marine clay offshore east Africa. The correlations were calibrated against 68 direct simple shear (DSS) strength measurements from clay samples, using CPT data collected near the boreholes.<br /><br />Four methods were evaluated: one based on net cone tip resistance (Method 1), one on effective cone tip resistance (Method 2), one on excess pore-water pressure (Method 3), and one on total cone tip resistance (Method 4). Method 1 requires soil unit-weight data; the other methods do not.<br /><br />The cone factors showed substantial variability, with coefficients of variation of 21%–31%. Method 4 had the lowest variability, followed by Method 1. However, Methods 2, 3, and 4 showed statistically significant dependence on depth, while Method 1 was relatively depth-independent. Methods 1 and 2 produced broadly comparable strength estimates, particularly in the upper 20 m. Method 4 also performed reasonably well, with estimates generally within about 5%–15% of Method 1. Method 3 was inconsistent: it tended to underestimate strength at shallow depths and overestimate it at greater depths.<br /><br />The authors conclude that Methods 2 and 4 can serve as alternatives when unit-weight measurements are unavailable, but their depth dependence should be considered. Method 1 remains a useful baseline where unit-weight data are available.

Keywords

cone penetration test

CPT correlations

undrained shear strength

deepwater marine clay

offshore east Africa

direct simple shear

cone factor variability

net cone tip resistance

excess pore-water pressure

site-specific calibration