A framework for project sustainability assessment and schedule optimization in multi-mode construction projects

Project scheduling and sustainability assessment are often conducted separately, limiting an organization’s ability to balance sustainability with cost efficiency. This study proposes an integrated framework for sustainable project scheduling that aligns economic, environmental, and social objectives. The framework has two stages. Stage 1 assesses sustainability through a three-tier hierarchical model, in which expert-selected criteria are evaluated using Fuzzy AHP (FAHP) and a Fuzzy Inference System (FIS). Stage 2 formulates a tri-objective sustainability-based multi-mode resource-constrained project scheduling problem (Sus-MRCPSP) to maximize net present value (NPV), environmental score, and social score. The framework embeds sustainability objectives at the project definition stage, enabling early integration into planning decisions. Because the problem is NP-hard, three metaheuristics, NSGA-II, MGWO, and SPEA2, are customized and tuned to solve the model. Computational experiments on standard benchmark problems of different sizes show that SPEA2 and MGWO outperform NSGA-II. A real-world case study validates the framework and shows that environmental and social outcomes can be improved with a potential trade-off in NPV. The results demonstrate the framework’s value for project managers who seek to prioritize sustainability alongside economic performance.