Optimised subgrade design for transport infrastructure: a Mechanistic-Economic approach

This article presents an integrated Mechanistic-Economic analysis for optimising transport infrastructure subgrades by combining a deterministic mechanical model with a data-based cost formulation. Mechanical behaviour is evaluated using a 3-D Boundary Element Method (BEM) based on a Green’s function for a semi-infinite multilayered system. Complementary subroutines analyse multiple sections formed by successive constructive lifts. The stiffness of compacted natural soils is adjusted via the Dormon & Metcalf criterion to capture the interaction with the underlying layers; conversely, stabilised soils are exempt from this rule and treated as engineered materials. The economic framework is developed through an inductive calibration process from data-based construction costs. The analysis comprises two complementary levels: a) global-scale sensitivity study simulating market variations; b) local-scale application using project–level scenarios. A systematic search is employed to map the Pareto front between vertical settlement and construction cost. The results identify optimal subgrade designs with different soil types and clarify the conditions under which each solution becomes favourable, supporting decision-making. This approach allows for regional cost updates without altering the mechanical core and is extendable to pavement structures, enabling integrated optimisation of both foundation and pavement layers.