$((((()))))"$In civil engineering, the interaction between soil and structures is pivotal for ensuring the stability and longevity of infrastructure. Considering the diverse geotechnical challenges posed by varying soil types and environmental conditions, how do engineers integrate theories of soil mechanics and foundation engineering to design robust and resilient foundations? Furthermore, in what ways do geotechnical investigations, including site characterization and soil testing, inform the selection of appropriate foundation systems and construction techniques to mitigate risks such as settlement, bearing capacity failure, and liquefaction in both urban and geologically complex settings?"