Contractors must comply with the rules to protect employees and to prevent OSHA citations. A matrix that is found in Appendix F of the standard summarizes the requirements for excavations twenty feet or less in depth. Initially, it must be determined whether or not the excavation will be greater than five feet in depth. If it will be five feet or less, excavation may be made with vertical sides, unless there is a potential for cave in. If the excavation is greater than five feet it may be made with vertical sides only if the excavation is entirely in stable rock.
Stable rock is defined as natural solid mineral matter.
Sloping Sloping can be used without soil classification only if a slope of 1 horizontal to 1 vertical can be maintained. Oftentimes this slope is not feasible so soil classification must be done. Visual Testing Soil particle size and type. It could be clay or silt. Cracks in walls and spalling can mean soil types B or C. Layered systems with adjacent hazardous areas buildings, roads and vibrating machinery may require a professional engineer for classification.