Applicability and improvement of soil classification methods in Delta regions based on the CPTU database

Several soil classification systems have been developed for specific sites based on the CPTU database. However, issues may occur when applying these existing soil classification methods to delta regions, whose construction sites involve deposits that are both weak and compressible. This requires further evaluation and a more detailed dataset. A database has been compiled that includes 85 CPTU soundings from 36 sites in the Yangtze River Delta. This study evaluates the performance of four existing CPTU-based soil classification methods for deltaic soils. The performance of each soil classification method is quantified by the micro F-1 score, the weighted kappa coefficient, and the chi-square value. An analysis and comparison indicate that the SBT chart has the highest accuracy, with a micro F-1 score of 0.72. The weighted kappa values for most of the soil classification methods can reach 0.5, which shows that there is a median degree of consistency in terms of the classified soil type. Hence, current soil classification methods need to be supplemented using local geological conditions and laboratory test results from borehole records. Therefore, a novel modified soil classification chart is presented herein to illustrate the deltaic soil conditions more accurately.