Comparative Assessment of Presumptive and Field-Based Soil Bearing Capacity in Cabanatuan City, Philippines

This research presents a geotechnical comparative screening between theoretical and empirical soil bearing capacities across 13 selected data nodes in Cabanatuan City. Utilizing the Philippine Geoportal database for initial soil classification, the study identified a subsurface dominated by Fine Sand and various Loams, reflecting the alluvial depositional history of the Pampanga River Basin. Theoretical baselines were established using IBC 2024 presumptive allowable bearing capacities, yielding a constrained range of 71.82 kPa to 95.76 kPa. Conversely, site-specific Standard Penetration Test (SPT) data from available DPWH borehole logs were analyzed. Using empirical correlations to derive allowable bearing capacities (qfield) from N-values, results revealed a highly heterogeneous subsurface ranging from 45 kPa to 225 kPa. While the IBC framework was conservative in 62% of locations, field-based values in 5 out of 13 sampled sites exhibited lower field-based values than the corresponding IBC presumptive values. This indicates potentially unconservative assumptions in specific zones if presumptive values are utilized without site-specific verification. The study concludes that international codes provide a necessary administrative baseline but cannot fully capture the observed 180 KPa variation among the investigated samples. Consequently, site-specific geotechnical investigations remain indispensable for ensuring structural integrity and design optimization in complex alluvial environments.