Which of the following could be categorized as an unforeseen obstacle on a construction site?

Undiscovered utility lines can significantly disrupt construction operations and are indeed categorized as unforeseen obstacles. These lines are typically not visible or documented in existing site plans, making them a hidden challenge that contractors may encounter unexpectedly. If a construction team strikes an undiscovered utility line, it can lead to project delays, safety hazards, and potentially costly repairs.

On the other hand, scheduled inspections, established project timelines, and standard safety protocols are all anticipated aspects of a construction project. They are typically accounted for in the project planning phase and do not present the same level of unpredictability as unforeseen obstacles like hidden utility lines. Proper planning can mitigate issues related to inspections and protocols while timelines are set to guide project progression.