CPT-based spatial variability of marine clay: a case study from Gwangyang Bay of Korea

This study investigates the spatial variability of Gwangyang marine clay at the southern-central coast of Korea using cone penetration test (CPT) soundings. A total of 51 CPT profiles were compiled and analyzed to evaluate the vertical correlation length based on the autocorrelation function (ACF) approach. Trend removal was applied to address the depth-dependent non-stationarity, and the weak stationarity of the residuals was quantified using Kendall's τ test. Sample ACFs of the stationary residuals were approximated using four theoretical autocorrelation models, namely, single exponential, squared exponential, cosine exponential, and second-order Markov models. The influence of the initial extent of the sample ACF on the correlation length was examined. The results indicate that the estimated correlation length of Gwangyang clay ranges from 0.10 m to 1.81 m, with limited sensitivity to the selection of the autocorrelation model. These values are comparable to those reported for onshore and nearshore clays worldwide. In addition, it is found that the fitting of the sample ACF is achieved across lag distances at or below Bartlett's limit. The findings contribute to the growing database of spatial correlation lengths for clays and support more reliable random field modeling of marine clays in geotechnical engineering practice.