What theoretical frameworks serve as the foundation for civil engineering disciplines? From classical principles to contemporary models, what are the core theories shaping structural engineering, transportation systems, environmental engineering, and geotechnical engineering? How do Newtonian mechanics, fluid dynamics, and material science underpin structural analysis and design? In transportation engineering, how do traffic flow theories and optimization models inform urban planning and infrastructure design? Moreover, in environmental engineering, what are the key theories governing water and wastewater treatment processes, air quality management, and solid waste management? Lastly, how do soil mechanics principles drive geotechnical engineering practices, including foundation design and slope stability analysis?