A coupled framework for the nonlinear analysis of piled raft foundations in heterogeneous and layered soils

This study introduces NLAPR, a nonlinear computational tool for analysing piled raft foundations in diverse soil profiles. NLAPR couples finite element, elastic continuum, and load transfer methods within a hybrid framework that captures soil nonlinearity and nonlinear pile responses; various soil conditions, including heterogeneous semi-infinite media, finite layers and multi-layered soils (semi-infinite or rigid-base); and pile groups with different lengths, diameters, and rigidities. NLAPR is validated through comparison with the published data for multiple raft and piled raft configurations in different soil profiles. Benchmark problems simulated using alternative programs and 3D FEA confirm its accurate and dependable predictions. A parametric study using NLAPR examines effects of piles number, pile length, raft thickness, soil stiffness, and load type on a piled raft in a finite soil layer under concentrated loads. Results show that increasing piles number and length enhances foundation stiffness, reducing total vertical settlement and raft load sharing, while slightly decreasing differential settlements and bending moments. Raft thickness primarily governs differential settlements but negligibly affects load distribution. Higher soil stiffness shifts behaviour from nonlinear to nearly linear and increases load concentration on central piles. In nonlinear analysis, as the load level increases, both piled raft settlement and the load carried by the raft increase. Crucially, treating concentrated loads as equivalent uniform loads substantially underestimates differential settlements and fails to capture accurate bending moments.