Development of SPT-N60 and USCS-based soil type zonation maps for Dhaka Metropolitan Development Plan (DMDP) Area, Bangladesh

This research paper has presented Unified Soil Classification System (USCS)–based soil type and Standard Penetration Test (SPT) N₆₀–based zonation maps in the Dhaka Metropolitan Development Plan (DMDP) area of Bangladesh. For this purpose, 360 borehole data have been collected from different parts of the DMDP area. The data were analyzed in ArcGIS 10.5 using Ordinary Kriging and Inverse Distance Weighting (IDW) interpolation techniques. The spatial Analyst, Ordinary Kriging method, has demonstrated better results for SPT-N₆₀-based, and IDW has provided superior outcomes of the USCS-based soil type zonation maps. This study has developed 13 SPT-N₆₀-based and USCS soil-type zonation maps for the DMDP area at 1.5 to 19.5 m depth. To assess the reliability of the zonation map, SPT-N₆₀ values and USCS soil classification, acquired through field tests at 10 locations (depths: 1.5 to 19.5 m), were compared with anticipated SPT-N₆₀ values and USCS soil type at exact coordinates in the developed zonation maps. The root mean square error (RMSE) for the SPT-N₆₀ zonation maps was 8.29 blows, and the coefficient of determination (R²) was 0.688. The comparison shows a correlation coefficient of 0.82. For USCS soil-type zonation maps, 55.81% of the field-validated data fully matched the model-anticipated USCS zonation maps data. The generated zonation maps in this research will help to understand the subsurface condition and geotechnical characteristics of soils in the DMDP area. This data will also help engineers to create an initial foundation layout for a new site using the existing data from the nearby locations.