What must be used when working in excavations that are not made in stable rock?

When working in excavations that are not made in stable rock, it is essential to use protective measures to prevent cave-ins and ensure worker safety. The correct answer reflects that multiple safety options can be utilized in such scenarios.

Excavations that are not in stable rock can present significant hazards, and ensuring the safety of workers involves either shoring, shielding, or sloping the excavation. Shoring involves using supports to prevent soil movement, while shielding usually refers to the installation of protective barriers to catch falling soil. Sloping the sides of an excavation reduces the angle of repose and minimizes the chances of soil collapse.

The mention of heavy machinery, hand tools, or shoring alone emphasizes that there are various approaches and equipment that can be used depending on the excavation's requirements and conditions. Therefore, the correct choice indicates that a combination of methods and tools can be effective for ensuring safety while working in potentially unstable soil conditions.