Time-cost-quality-risk Trade-off Project Scheduling Problem in Oil and Gas Construction Projects: Fuzzy Logic and Genetic Algorithm

Time, cost and quality, known as project iron triangle, are among the important goals and objectives of any project. New agreements in construction industry, which pay more attention to the quality of project implementation while reducing time and cost, demonstrate the growing importance of these three primary objectives of projects. In this paper, an optimization model with three objective functions of cost, risk and quality considering their relationships with time is presented. In the cost objective function, the associated costs of compressing project activities together with the costs of delay are taken into account. The risk objective deals with the probability of risk occurrence and its impact on project other objectives. The quality objective function expresses the degree of reduction in the quality level of compressed activities. The model was also validated by solving the small-size problems with the exact method and NSGA-II algorithm (Non-dominated Sorting Genetic Algorithm). The proposed model was implemented in a construction project of oil storage tanks. Due to the NP-Hard and large-sized problem, the model was solved by using the metaheuristic NSGA-II algorithm. The results showed that the NSGA-II algorithm achieved close to the optimal solution. Therefore, the NSGA-II algorithm can be exploited for solving large-size problems with more confidence.