How do soil mechanics and foundation engineering principles interplay in the design and construction of civil engineering structures? Elaborate on the key concepts, such as soil classification, bearing capacity, and settlement analysis, and discuss their significance in ensuring the stability and longevity of various infrastructure projects. Furthermore, delve into the methodologies used to assess soil behavior under different loading conditions, including laboratory testing and in$-$situ investigations. Consider the role of geotechnical engineering in mitigating risks associated with soil$-$related hazards, such as landslides and liquefaction, and analyze the factors influencing the selection of suitable foundation types, such as shallow foundations, deep foundations, or ground improvement techniques. Additionally, examine the influence of environmental factors, such as water content and geological formations, on soil mechanics principles, and evaluate the implications for sustainable construction practices.