Which tool is essential for the operation of pit dry boring machines?

The essential tool for the operation of pit dry boring machines is a piercing tool. This tool is specifically designed to facilitate the process of boring through the ground to create a pathway for utilities or piping. When utilizing a pit dry boring machine, the piercing tool aids in the initial penetration into the ground by breaking up the material in front of the drill, allowing for easier and more effective advancement of the boring process.

In contrast, other tools mentioned in the options serve different functions. A vibrating plow is primarily used for direct burial of cables or pipes in the ground without the need for traditional trenching. A directional drill is employed for trenchless construction techniques, typically in larger-scale projects, and while it is effective for certain types of underground installation, it is not specifically associated with pit dry boring. Lastly, a trenching shovel is a manual tool that assists with digging trenches and is not relevant in the mechanized context of pit dry boring. Understanding the specific purpose of each tool helps to clarify why the piercing tool is fundamental to the operation of pit dry boring machines.