How do varying soil properties affect the design and construction of deep foundations in civil engineering projects? Discuss the implications of soil composition, density, moisture content, and shear strength on the selection and sizing of pile foundations, considering both cohesive and non$-$cohesive soils. Analyze the influence of factors such as settlement, bearing capacity, and lateral load resistance on the choice between different types of deep foundations, such as driven piles, drilled shafts, and micropiles. Furthermore, explore the role of site investigation techniques, including geotechnical testing and soil sampling, in characterizing soil behavior and informing foundation design decisions. Evaluate the challenges posed by heterogeneous soil conditions and propose strategies for mitigating risks associated with uncertainties in subsurface soil properties during the design and construction phases of civil engineering projects.