How do soil mechanics principles influence the design and construction of civil engineering projects? Explore the interplay between soil properties, such as grain size distribution, moisture content, and compaction, and their impact on foundation stability, bearing capacity, and slope stability. Discuss the significance of soil classification systems like the Unified Soil Classification System $($USCS$)$ and their role in determining appropriate construction methods and materials. Analyze the importance of site investigation techniques, including geotechnical testing and sampling methods, in assessing soil behavior and identifying potential hazards such as settlement, liquefaction, and landslides. Consider the implications of various ground improvement techniques, such as soil compaction, stabilization, and reinforcement, in mitigating soil$-$related risks and enhancing the performance and longevity of infrastructure projects. Evaluate the role of advanced computational tools, such as finite element analysis $($FEA$)$ and numerical modeling, in simulating soil$-$structure interaction and optimizing design parameters to ensure the safety, reliability, and sustainability of civil engineering works.