Excavation, Trenching, and Shoring Practices
Definitions that decide the rules
An excavation is any man-made cut, cavity, or depression in the ground. A trench is a narrow excavation deeper than it is wide, with a bottom width generally not exceeding 15 feet. Every trench is an excavation, but not every excavation is a trench.
The numbers to memorize
- 5 feet: protective systems (sloping, benching, shoring, or shielding) are required for trenches 5 feet deep or more, unless the excavation is entirely in stable rock. Many jurisdictions use 4 feet - follow the stricter rule.
- 20 feet: excavations deeper than 20 feet require a protective system designed by a registered professional engineer.
- 2 feet: spoil, equipment, and materials are kept at least 2 feet back from the edge.
- 4 feet: ladders or other safe access are required once a trench reaches 4 feet deep, and workers must be within 25 feet of lateral travel to reach one.
- Daily: a competent person inspects the excavation before entry, at the start of each shift, and after rain or any event that could change conditions. The competent person can identify hazards and has authority to stop work.
Slope ratios by soil type
Type A (cohesive): ¾:1. Type B: 1:1. Type C (granular, submerged, or previously disturbed): 1½:1. Stable rock may be cut vertical.
Other controls
Locate utilities before digging, watch for water accumulation and atmospheric hazards, keep heavy equipment back from the edge, and never let workers stand under suspended loads or raised buckets.
Traps in questions
Expect confusion among 4, 5, 20, and 25 feet, and among slope ratios. Another trap: assuming soil type must be proven by lab testing - a competent person may classify by visual and manual examination.
Rule of thumb
Remember the sequence 5–4–2–25: protect at 5 feet, ladder at 4 feet, spoil 2 feet back, ladder within 25 feet.