OSHA Trench Sloping Calculator

This calculator helps determine OSHA-compliant trench slope dimensions based on the soil classification system defined in 29 CFR 1926 Subpart P. It supports both sloping and benching protection methods.

OSHA Soil Classification

OSHA classifies soil/rock into four categories based on stability, from most stable to least:

• Stable Rock: Vertical walls permitted (90°)
• Type A: 3/4H:1V slope (53°) — cohesive soils, ≥1.5 tsf
• Type B: 1H:1V slope (45°) — cohesive soils, 0.5–1.5 tsf
• Type C: 1-1/2H:1V slope (34°) — granular/weak soils, ≤0.5 tsf

Slope Setback Formula

The setback per side = depth × horizontal slope ratio. The top-of-trench width = bottom width + 2 × setback. For example, a 10 ft deep trench with 2 ft bottom width in Type C soil has a setback of 10 × 1.5 = 15 ft per side, for a top width of 32 ft.

Benching Rules

• Type A: Maximum 5 ft bench height, minimum 2 ft horizontal step
• Type B: Maximum 4 ft bench height, step width per slope ratio
• Type C: Benching is NOT permitted
• Stable Rock: Benching is not applicable (vertical walls allowed)

PE Requirement

Excavations deeper than 20 feet (6.096 meters) require design by a registered professional engineer per OSHA 29 CFR 1926.652(b), regardless of soil type.