Research on the Impact of Contractual Governance and Relational Governance on Project Quality Performance in Megaprojects—With Contractors’ Opportunistic Behavior as a Mediating Factor

重大工程项目是我国经济社会发展的重要引擎，具有深远的经济、社会和战略意义。但因其高度的不确定性和复杂性等特点，项目质量绩效水平常常难以达到预期。为解决上述问题，本文从项目治理角度出发，深入剖析合同治理、关系治理对重大工程项目质量绩效的影响机制，并考虑承包商机会主义行为在其中的中介作用。文章基于交易成本理论、委托代理理论和社会交换理论，提出假设并构建理论模型。在此基础上，采用问卷调查方式收集数据，并运用偏最小二乘结构方程模型(PLS-SEM)方法进行实证分析。结果表明：基于重大工程项目情境，合同治理能显著抑制承包商机会主义行为，促进项目质量绩效提升；关系治理与承包商机会主义行为呈显著“U型”关系，与项目质量绩效呈显著“倒U型”关系；承包商机会主义行为与项目质量绩效呈显著负相关关系，且在合同治理、关系治理与项目质量绩效的关系中起部分中介作用。研究表明，合同治理是保障项目质量水平的重要机制，揭示了关系治理的“双刃剑”效应，并强调对承包商机会主义行为的关注和抑制，为重大工程项目治理实践提供了重要启示。Megaprojects are a vital driver of China’s economic and social development, carrying profound economic, social, and strategic significance. However, due to their high levels of uncertainty and complexity, the quality performance of these projects often fails to meet expectations. To address this issue, this paper adopts a project governance framework to explore the impact mechanisms of contractual governance and relational governance on the quality performance of megaprojects, while considering the mediating role of contractors’ opportunistic behavior. Grounded in transaction cost theory, principal-agent theory, and social exchange theory, this paper puts forward hypotheses and constructs a theoretical model. Subsequently, data was collected through questionnaires and analyzed using the partial least squares structural equation modeling (PLS-SEM) method. The results show that, within the context of megaprojects, contractual governance can significantly inhibit contractors’ opportunistic behavior and enhance project quality performance. Additionally, there is a significant “U-shaped” relationship between relational governance and contractors’ opportunistic behavior, and a significant “inverted U-shaped” relationship between relational governance and project quality performance. Furthermore, contractors’ opportunistic behavior is significantly negatively correlated with project quality performance and plays a partial mediating role in the relationships among contractual governance, relational governance, and project quality performance. The research indicates that contractual governance is a crucial mechanism for ensuring project quality. It reveals the “double-edged sword” effect of relational governance and emphasizes the importance of monitoring and mitigating contractors’ opportunistic behavior, providing valuable guidance for the governance practice of megaprojects.