Between 1990 and 2000, 771 deaths were attributed to trench collapse in the United States. Trenches are deep holes dug into the soil for the purpose of construction, in most cases. Supporting trench walls to prevent trench collapse is important for the safety of the workers. Effective forms of trench safety include sloping, shoring, and shielding.
Sloping walls may help to prevent trench collapse by shifting soil weight away from workers. Sloping involves digging trench walls at an angle leading away from the trench opening. The end result looks similar to a funnel, with extra soil deposited far from the opening. Soil removal is also important to preventing trench collapse. If it is placed immediately outside trench walls, increased weight may affect wall strength.
Shoring trench walls involves placing metal plates on either side of the trench. Walls can be kept in place with spacers that are cut to match trench width, or by use of a hydraulic system. Hydraulics provide constant, even pressure on walls to prevent collapse.
Pressure may be adjusted to match wall width. For instance, if trench walls narrow, hydraulic pressure can be released to narrow shoring plates. The opposite is also true. Even pressure is placed on walls to prevent trench collapse. Shoring usually only supports two sides of the trench.
Shielding is similar to shoring, but, with this method, all four sides of the trench can be protected. One common shield type is the trench box. Trench boxes are often assembled outside the trench and lowered into place. Many boxes come in standard sizes, typically ranging from 8 feet (approximately 2.4 m) to 24 feet (approximately 7.3 m).
Spacers placed between shields hold the barriers in place. Barrier width is often adjusted by removing spacers that are too long or too short, and replacing them with dividers of correct size. Hydraulics are not typically used with trench boxes.
Slide rail systems, another shielding used to prevent trench collapse, may be more effective in certain types of excavation. Slide rail systems usually include metal walls lowered into a trench. Braces with attached rollers are used to hold barriers in place. The rollers allow for easy assembly and removal of retaining walls. Slide rails can be moved as trenches deepen, with additional panels easily added to increase length and height.
Contractors and construction workers commonly undergo training on trench collapse before beginning work on an excavation site. Education about the dangers associated with trench building may decrease the number of job-related injuries. In the United States, safety precautions are required by the Occupational Safety and Health Administration (OSHA).