Safety in the construction industry remains a major challenge despite the technological advancements made in recent years. In recent years, ontologies are applied to give a formal structure to the knowledge in different domains. Ontologies also facilitate the integration of various domain knowledge and thus allow for better cross-functional developments (e.g., operator support systems that consider safety and productivity at the same time). The authors have previously developed a comprehensive Earthwork Ontology (EW-Onto). However, there has been no linkage between safety regulations and EW-Onto. Therefore, this research aims to: (1) develop a formal representation of earthwork safety regulations knowledge, and (2) integrate this knowledge with EW-Onto. A case study is developed to validate the integrated ontology. It is shown that the integrated ontology can be used to bridge the gap between high-level safety regulations and task-level instructions.