Deep Excavations (Over 20 Feet)

The deeper the hole, the greater the force on its walls, and the harder it is to get out. OSHA treats excavations more than 20 feet deep differently: the protective system must be designed by a registered professional engineer. Standard tables, trench boxes and slope charts are not enough.

• Construction
• Excavation
• Heavy Civil

The 20-foot rule

• Excavations 5 feet or deeper need a protective system unless they’re in stable rock (29 CFR 1926.652). See Protective Systems.
• When an excavation is more than 20 feet deep, the protective system must be designed by a registered professional engineer (1926.652). A competent person alone can’t select a system from the standard tables for that depth.
• The design must account for the soil, depth, water, nearby structures, traffic and equipment loads, and how the system will be built, used and removed.
• The employer must keep a copy of the design at the site while the excavation is open, and follow it exactly.

Common systems for deep work

• Sheet piling: interlocking steel sheets driven into the ground, braced with wales and struts or tied back with anchors.
• Soldier piles and lagging: steel beams set in the ground with wood or concrete lagging between them.
• Slurry or secant walls and soil nailing for large, permanent excavations.
• Engineered shoring and shields built for the depth and loads. A standard trench box isn’t rated for over 20 feet unless the maker’s data and an engineer approve it. See Trench Boxes and Hydraulic Shoring.
• Benching and sloping: only as the engineer designs. Very deep slopes need a large footprint.

Bigger hazards at depth

• Greater soil pressure and collapse volume. A deep cave-in buries people quickly and rescue is very hard. See Trench Emergencies.
• Water and groundwater can undermine walls and create flooding. See Dewatering.
• Hazardous atmospheres: gas can collect at the bottom. Test before entry and monitor. See Trench Atmospheres.
• Falling objects: tools, soil, rocks and equipment. Keep spoil and equipment back. See Surcharge Loads and Barriers & Fall Protection at Excavation Edges.
• Nearby structures and utilities can shift when the ground moves. Monitor them. See Excavations Near Structures and Supporting Exposed Utilities.

Access, egress and rescue

• OSHA requires a way out within 25 feet of lateral travel for workers in trenches 4 feet or deeper. In a deep hole that usually means stairways, ramps or ladder towers designed for the depth. A single ladder is not enough for long climbs. See Access, Egress & Spoils.
• Plan rescue before work starts: who calls, who is trained, what equipment is on site (such as a hoist, harness and retrieval line), and how emergency services will reach workers. Many fire departments can’t do deep trench rescue, so call early.
• Keep a count of everyone who is in the excavation.
• Provide lighting, communications and emergency lighting for deep work.

Inspections and records

• A competent person inspects the excavation, the protective system and the adjacent area daily before work and after rain, thawing, vibration or other changes. See Competent Person Inspections.
• Instrumentation, such as monitoring points on nearby buildings or walls, may be required by the engineer.
• Keep the designer’s drawings and any changes on site and follow the removal sequence when backfilling. See Backfilling & Compaction.

Deep excavation checklist

• Protective system designed by a registered professional engineer and on site
• No changes made to the system without the engineer’s approval
• Safe stairs, ramps or ladders sized for the depth
• Rescue plan, equipment and communications ready
• Atmosphere tested and water controlled
• Daily inspection by a competent person, with records

Last updated: October 4, 2026