Which of the following is a disadvantage of using drilled shafts for substations?

Using drilled shafts for substations presents various challenges, one of which is the necessity for specialized equipment. Drilled shafts, often referred to as bored piles, require heavy machinery capable of boring deep holes into the ground to create strong foundations. This equipment is typically larger and more complex than what is needed for other types of foundations, such as shallow foundations.

The need for this specialized equipment can lead to increased costs associated with both the rental or purchase of machinery and the labor required to operate it. Additionally, logistical considerations, such as transportation and setup of this heavy equipment on-site, further add to the complexity and potential delays in construction timelines.

In contrast, the other options, such as durability, environmental impact, and cost, do not highlight inherent disadvantages of drilled shafts in the same way. The durability of drilled shafts might be an advantage compared to certain other foundation types, while their environmental impact can be less than that of more invasive techniques. Lastly, drilled shafts are generally not lower in cost; in many cases, they are more expensive due to the expertise required for installation and the specialized equipment needed.