Why is a depth of 8 feet recommended for pile tips in certain foundations?

A depth of 8 feet for pile tips in certain foundations is recommended primarily because it helps to prevent lifting from flooding. When foundations are not deep enough, the upward force created by rising water levels can displace or lift the foundation, compromising the stability of the structure. By extending pile tips to this depth, the foundation can achieve sufficient embedding into stable soil layers, which not only provides better support but also mitigates the risks associated with water movement, such as erosion or flotation. This depth is particularly relevant in areas prone to flooding, ensuring that the foundation remains secure and effective in anchoring the structure during extreme weather events.

Other options, while potentially relevant to construction practices, do not directly address the critical issue of structural stability against floodwaters, making them less pertinent in this context.