What type of pile includes an enlarged base or bulb formed during driving?

The correct answer is bulb piles, which are characterized by their enlarged base or bulb that is formed during the driving process. This distinctive design provides increased bearing capacity as the bulb spreads out the load over a larger area, enhancing stability and resistance to settlement in various soil conditions. Bulb piles are particularly useful in scenarios where the soil's load-bearing capability is a concern, as the bulb can effectively transfer the load to deeper, more stable soil layers.

This type of pile is often used in foundation engineering where deeper penetration is needed, and the bulb improves the structural integrity of the pile by distributing the load better than a standard cylindrical pile would. The unique feature of the bulb distinguishes it from other pile types, such as bored piles, which are constructed without any specific enlarged base, and sheet piles, which are used for lateral support rather than vertical load-bearing. Timber piles also do not have a bulbous feature, as they usually consist of cylindrical wood members. Thus, bulb piles are specifically designed for enhanced support due to their shape.