How do soil mechanics and geotechnical engineering principles influence the design and construction of deep foundation systems in civil engineering projects? Explore the various factors such as soil composition, groundwater conditions, and geotechnical properties that engineers must consider when selecting and designing deep foundation solutions. Additionally, discuss the role of site investigations, laboratory testing, and numerical modeling techniques in assessing soil behavior and determining the most suitable foundation type for different soil profiles and loading conditions. Consider the challenges posed by complex geological formations and seismic activity, and analyze how engineers mitigate risks and ensure the stability and performance of deep foundation systems over the lifespan of structures.