ANS:D - square with corners chamfered.

A precast pile is typically used in foundation construction, and various shapes are available depending on the specific requirements of the project. Among the options provided:

• Circular: Circular precast piles are commonly used. They offer uniform load distribution and are well-suited for resisting lateral forces. The circular shape also provides efficient load transfer to the surrounding soil.
• Square: Square precast piles are also popular. They provide stability and ease of installation, especially in cohesive soils. The square shape offers better resistance to torsional forces compared to circular piles.
• Octagonal: Octagonal precast piles offer a compromise between the stability of square piles and the load distribution of circular piles. They are suitable for a wide range of soil conditions and are often used in projects where both lateral and vertical loads are significant.
• Square with corners chamfered: Square precast piles with chamfered corners combine the stability of square piles with reduced soil resistance during installation. The chamfered corners help reduce resistance to penetration into the ground while maintaining stability.

Ultimately, the choice of precast pile shape depends on factors such as soil conditions, structural requirements, installation methods, and project-specific considerations. Each shape has its advantages and limitations, and the selection should be based on engineering analysis and design requirements.