Comparative Evaluation of Shallow and Deep Foundation Design in Variable Cohesionless-Cohesive Soil Strata: A Structural-Geotechnical Perspective

The foundation of a building serves as the critical structural interface transferring superstructural static dead loads, dynamic live loads, wind forces, and seismic base shears safely into the underlying geologic soil strata. Structural failure occurs when applied contact stresses exceed the ultimate bearing capacity or when total and differential settlements violate permissible Serviceability Limit State (SLS) criteria. This paper presents an analytical investigation into the structural and geotechnical performance of foundation typologies—ranging from isolated reinforced concrete pad footings and combined footings to raft/mat foundations and bored cast-in-situ concrete piles. Classical bearing capacity models (Terzaghi, Meyerhof, Hansen, and Vesic) are coupled with elasticity theory and Terzaghi's 1D consolidation theory to establish an integrated performance benchmark across dense sand, medium-stiff cohesive-frictional soil, and highly compressible saturated marine clay. Results indicate that while isolated shallow foundations are highly cost-efficient in dense cohesionless strata, soft cohesive soils necessitate large mat or deep pile foundations to achieve an 86.7% reduction in total settlement, effectively mitigating pressure bulb overlapping, differential tilt, and structural secondary bending moments in the building superstructure.