task : $8\mathrm{.}90$#What are the fundamental theories that underpin the field of civil engineering? How do these theories encompass various principles such as structural mechanics, fluid dynamics, and materials science to address challenges in infrastructure design, construction, and maintenance? Additionally, how do theoretical frameworks like elasticity, plasticity, and fluid flow theory contribute to understanding and predicting the behavior of civil engineering structures under different loading conditions? Furthermore, how do advancements in computational methods and modeling techniques enhance the application of theoretical principles in analyzing and designing civil engineering systems, ensuring safety, sustainability, and efficiency in infrastructure projects?