give me correct answer$\_\_\_\_\_\_\_$ the significance of soil mechanics in civil engineering, emphasizing its role in foundation design and construction. Explain the fundamental principles governing soil behavior, including soil classification, compaction, and shear strength. Furthermore, analyze the impact of soil properties such as grain size, moisture content, and density on the stability and settlement of structures. Elaborate on common methods used to assess soil properties, such as laboratory tests and field investigations. Provide examples of real$-$world engineering projects where a comprehensive understanding of soil mechanics is essential for ensuring the safety, durability, and cost$-$effectiveness of infrastructure development."