Why is a shield also referred to as a trench box?

A shield is referred to as a trench box primarily because it is designed to be portable and can move along with the work. This characteristic is essential for excavation projects, as it allows operators to use the shield effectively in different sections of a trench without needing to set up a new structure each time. The design of a trench box facilitates safe excavation by providing an enclosure that supports the sides of the trench, thereby preventing collapses and protecting workers from cave-ins.

While trench boxes can indeed be used in trench excavations and may be larger than some other shields, the key aspect that makes it a "trench box" is its mobility and ease of relocation during ongoing excavation tasks. This portability enables workers to create a safer work environment while efficiently managing the flow of the excavation project.