Trench Box

Trench boxes consist of two parallel steel or aluminum panels connected by adjustable spreader bars that hold the panels apart at the desired width. The box is lowered into the excavation using a crane or excavator, and workers perform their tasks from within the protected area between the panels. If the excavation walls collapse, the trench box panels prevent the soil from reaching the workers.

Trench boxes are less commonly used in hydrovac excavation than in traditional trenching because hydrovac holes are typically smaller in area and workers rarely need to enter them. However, for larger hydrovac excavations such as bell holes, pit excavations, or any situation where workers must enter an excavation deeper than 5 feet, a trench box may be the most practical form of cave-in protection.

Trench boxes must be rated for the depth at which they are used and the type of soil they will restrain. They must extend at least 18 inches above the surrounding grade to help prevent material from falling into the excavation. Trench boxes must be inspected before each use by the competent person and removed carefully to prevent the excavation walls from collapsing during extraction.