CPTU– <i>V</i> _s correlations incorporating the soil behavior type index: A case study from the Lingdingyang offshore area

Shear–wave velocity (Vs) is required for small–strain stiffness characterization and seismic site–response analyses. In estuarine–marine settings, direct Vs measurements are often sparse, whereas piezocone penetration testing (CPTU) data are commonly available. This study compiles 237 paired CPTU–Vs data points from six matched borehole pairs in the Lingdingyang offshore area of the Pearl River Estuary, where soft fine–grained deposits are interbedded with sand layers. To account for soil–type effects in a unified manner, the soil behavior type index (Ic) is incorporated to recalibrate two representative CPTU–Vs correlations and to develop an Ic–explicit formulation that provides a smooth transition between sand–like and clay–like trends. Model uncertainty and generalization are evaluated using borehole–clustered bootstrap resampling and leave–one–borehole–out cross–validation. The proposed Ic–explicit model achieves low prediction errors (MAE = 24.33 m/s) with a good fit (R2 = 0.85) on the compiled dataset, and shows no evident systematic residual bias with respect to cone tip resistance or Ic, particularly in mixed–soil intervals. The resulting correlation offers a practical approach for constructing Vs profiles in the Lingdingyang offshore area with abundant CPTU data but limited Vs measurements.