For the most part, residential construction doesn’t get involved in situations where open trenches and excavations are greater than five feet in depth. However, situations concerning deeper excavations and trenches come into play whenever high retaining walls or formed basement walls are involved. For these reasons, residential home builders should be aware of the regulations and accepted practices in dealing with excavation and trench safety.
The code of federal regulations (CFR) sets forth acceptable related practices under CFR Part 1926.650; Subpart P – Excavations and Trench Safety. These standards are available on-line. These standards apply to all open excavations made on the earth’s surface, including trenches.
This paper is not intended to cover the details of these regulations. It is presented as a general summary regarding what can be anticipated regarding the application of those standards.
All parties who are involved in excavations of any type are responsible for the awareness and knowledge of appropriate excavation standards and procedures.
First of all, excavations must be preceded with proper notification of all owners of possible underground utility facilities.
All excavations of a depth of five feet or greater falls within the jurisdiction of these regulations. Protection of employees in excavations of some approved form is necessary for any and all excavations of depths of five feet or greater.
Several methods of excavation protection systems are depicted by the applicable CFR regulations. These methods are noted.
Allowable Configurations and Slopes – Excavation protections is provided by slopes or benches of depths from zero to twenty feet at a rate of 3/4 horizontal to 1 vertical ratio for Type “A” soils, a rate of 1 horizontal to 1 vertical for Type “B” soils, or 1 1/2 horizontal to 1 vertical for Type “C” soils.
Type “A”, “B”, and “C” soils are described by the regulations, and can be determined at each excavation site by an individual who has been certified to do so. Essentially, Type “A” soils are sound, cohesive, and stiff soils that are undisturbed; Type “B” soils are moderately firm cohesive soils that are undisturbed; and Type “C” soils are non-cohesive, loose, and/or soft soils.
For excavations less than five foot of depth, vertical walls are acceptable as long as the soils are undisturbed an considered competent.
Excavations in stable rock can be cut vertically as long as no falling hazards are anticipated up to depths of twenty feet. All determinations must be provided by a properly certified competent individual.
It is noted that any excavation taken to depths greater than twenty feet must be designed by a qualified professional engineer.
Shields and Shoring – The use of properly designed shields or shores are appropriate for some excavation circumstances. The CFR guidelines provide acceptable configurations for shoring designs.
Shores act to prevent movement of soil excavation walls. Shields are designed to protect personnel from possible excavation wall failure. Shores and shields must also be designed to accommodate the Type “A”, “B”, or “C” soils that may be encountered. Again, any excavation greater than twenty foot of depth must be designed by a qualified professional engineer.
In some configurations, it may be appropriate to use combinations of excavation slope/benches, shores, and/or shields.
Other issues such as egress into and out of the excavation must be satisfied. Confined space considerations may be necessary.
All in all, the supervisor of all excavation operations is responsible for all issues of excavation and trench safety. He is expected to possess the knowledge provided by these applicable codes of federal regulations.