Multiobjective Optimization of Drilled Shafts in the Circunvalación Norte Viaduct Using Pareto-Front Analysis-Paper

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The study applies multiobjective optimization to the drilled-shaft foundations of Costa Rica’s Circunvalación Norte viaduct, balancing construction cost against structural safety. The authors use NSGA-II and Pareto-front analysis to compare deterministic design optimization (DDO), targeting a factor of safety (FS) of 3.0, with reliability-based design optimization (RBDO), targeting a probability of failure (Pf) of 0.001. Shaft diameter and length are varied, and RBDO represents soil-strength uncertainty using data from 138 pressuremeter tests and Monte Carlo simulations.<br /><br />For an axial load of 2,500 kN, the DDO optimum is a 1.0 m diameter, 21.0 m long shaft, with an estimated cost of 15,751. The RBDO optimum meeting the Pf target is 1.1 m in diameter and 10.5 m long, costing 8,810. This reliability-based option is substantially less expensive, although its FS is 2.21—showing that a lower FS can still correspond to acceptable reliability when soil variability is considered. The study also finds that shaft diameter influences cost and resistance more strongly than length, while higher resistance generally corresponds to lower failure probability.<br /><br />Sensitivity analysis and clustering further distinguish robust, risky, and unnecessarily expensive designs. Overall, the findings suggest that probabilistic safety criteria can capture geotechnical uncertainty more realistically than deterministic factors of safety and support more economical designs. The authors present Pareto-front analysis as a useful decision-making framework for this project and other large infrastructure developments.

Keywords

multiobjective optimization

drilled-shaft foundations

reliability-based design optimization

deterministic design optimization

NSGA-II

Pareto-front analysis

factor of safety

probability of failure

Monte Carlo simulation

geotechnical uncertainty