$92\mathrm{.}46\mathrm{.}834$In civil engineering, foundational theories underpin design, construction, and maintenance. Theorems like Euler$-$Bernoulli beam theory define structural behavior under load, crucial for bridge and building design. Soil mechanics principles, such as Terzaghi's effective stress theory, govern soil behavior, vital for foundations and retaining structures. Fluid mechanics laws like Bernoulli's principle inform hydraulic system design for water supply and drainage. Traffic flow theory models vehicular movement to optimize road networks. Structural analysis methods like finite element analysis apply mathematical principles to simulate complex structures' behavior. These theories serve as the backbone, ensuring safety, efficiency, and sustainability in civil engineering projects.