Trench boxes are steel or aluminum structures used in construction to extend the life of a trench and keep workers safe. They are made of shields and braces, and can be permanent or portable. Trench boxes improve stability and promote worker safety, and are subject to government safety standards.
Trench boxes are steel or aluminum structures that serve the dual purpose of extending the stable life of a trench and helping keep workers safe while jobs are being completed. Depending on the location and primary purpose, these boxes may also be known as sewer boxes, manhole covers, trench screens or tap boxes. These are almost always used in the context of construction, typically when workers are laying foundations for the first time, but also when they need to make underground repairs to things like cables or pipes. Digging trenches is a necessary part of most construction and engineering jobs. When digging a building’s foundation, laying pipes or telephone lines, installing valves, or doing a variety of underground work, the trenches, and often more specifically the boxes within those trenches, are where the Work.
How they are made
The physical construction of the medium box is usually pretty straightforward. Most consist primarily of two plates, also known as “shields,” which are typically made of steel. Shields line the walls of the trench and are supported by spreaders. These spreaders, also known as braces, are typically beams or bars set perpendicular to the steel plates holding up the trench walls. The plates and braces are bolted or welded together. The bottom edge of the box is at the bottom of the trench while the top edge of the box extends over the top of the trench. In addition to adding stability, this feature also makes getting in and out easier, at least in most cases.
Most of the time, the boxes are designed for workers to do their jobs within the plates of the box. As a result, the retractors or braces are placed as out of the way as possible. In the event of a trench rupture, the soil is retained by the outer walls of the box.
Permanent versus portable
Trench boxes can be permanent or portable. Portable ones are usually hauled along the trench by a backhoe or other mechanism using chains, cables and hooks as the work progresses. Permanent boxes cannot be moved along a trench line. However, their permanence is usually more about stability of position than anything else; they are almost always removed once the job is complete, but getting them out often takes more effort.
Pre-made boxes are often available for purchase, although depending on the job it might make more sense to arrange for them to be custom built. Much depends on the specifics of the trench and the nature of the project. The design and materials used in making a trench box can vary and typically depend on a variety of factors, including soil depth and soil composition.
Extend stand-up time
One of the biggest benefits of these boxes is that they improve the stability of a trench as a whole. Trenches typically have something called a hold time. This is the amount of time a trench will last from the time it is dug to the time its walls begin to give way. The waiting time can be from a few seconds to several months, depending on factors such as depth, soil type, soil water content, weather conditions, and activity around the trench. A properly positioned and mounted box will usually give workers more control over trench stability and overall stand-up time.
Promote worker safety
Even with the safety precautions of today’s modern construction companies, trench work has the potential to be extremely dangerous. In the United States alone, hundreds of people are killed every year and many more are injured as a result of trench collapses. Specially designed boxes are often used as a means of adding protection and mitigating the risk that workers could be trapped or seriously injured should the trench wall collapse. Accidents can still happen, but with boxes they are usually much less likely.
normative
Government safety authorities often establish safety and depth rating standards for the construction of trench boxes or shields, usually in the name of quality assurance and standardization of industry best practices. The depth rating determines the depth of a trench that a box can effectively resist the forces imposed by a potential collapse. Registered professional engineers typically determine a box’s depth rating and stamp their approval on the boxes.
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