Trench Box vs. Trench Shield: What’s the Difference?

Trench boxes, aka trench shields, are strong and versatile protective systems.

What’s the difference between a trench box, shore box and a trench shield? Nothing. They are all terms used to refer to the same common type of trench protective system.

A trench box, or trench shield, protects the workers inside it in the event of a trench wall collapse. It also shields workers from falling or dislodged materials. It does not shore up the trench walls or prevent a collapse.

The sidewalls of a trench box are available in single-wall or double-wall models, made of steel or aluminum, or sometimes a combination of the two. They are held in position by spreader bars, which prevent them from moving inward if a trench wall collapses. The spreaders are generally made of steel.

The capacity of a trench box is determined by the combined strength of the vertical and horizontal internal and external components. Sidewalls of a box can range from 3 inches to 12 inches thick.

Contractors install trench boxes for a variety of jobs, including digging foundations and installing or repairing utility lines. They are often used to achieve greater open spans. Most manufacturers make extremely long boxes to accommodate longer pipe or larger structures.

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Trench boxes come in different sizes and configurations. They range from 6 feet to 40 feet long and can be anywhere from 4 feet to 10 feet high. The length of the spreader bar determines the width.

Modular aluminum trench boxes are completely customizable using an assortment of panels and adjustable spreaders. Configurations can range from one-sided to four-sided. Because there is so much flexibility in how they can be assembled, care must be taken to assemble them only in a configuration allowed by the manufacturer.

Manhole boxes are square and designed for use where a manhole is to be placed in the linear run of pipe. The trench for the pipe is typically narrower than the area where the manhole would be placed. The manhole box has open slots on the wing walls to allow the pipe to run through.

When considering whether to use a steel or aluminum trench box, contractors should focus on the manufacturer’s tabulated data for the box, which dictates the configuration, placement and depth at which it can be used. At certain depths, especially for smaller jobs, a lighter, easier-to-move aluminum trench box can be just as effective as a much heavier steel trench box. For deeper excavations, trench boxes can be stacked and secured on top of each other.

Depending on the site requirements, trench boxes can be used alone or in combination with other protective systems. When using a trench box, contractors must follow the instructions in the manufacturer’s tabulated data or use a professional engineer to design the system if the limitations of the tabulated data are exceeded.

With more than 100 trench safety branches and the largest fleet of shoring and underground excavation rental equipment in North America, United Rentals can help you find the right solution for your excavation needs. Contact the Trench Safety group today.

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