Trench Sloping Calculator: OSHA 1926.652 Soil Type Slope Ratios

How It Works

1. Classify the Soil

   Use OSHA Appendix A tests to classify soil. Type A is hard cohesive clay (1.5+ tsf). Type B is medium cohesive or granular with some cohesion (0.5-1.5 tsf). Type C is soft clay, sand, gravel, or submerged soil (under 0.5 tsf). Stable Rock allows vertical cuts.

2. Enter Trench Dimensions

   Input the trench depth, bottom width, and length. Trenches deeper than 5 feet require protective systems unless entirely in stable rock. Trenches over 20 feet require an engineered design.

3. Calculate Slope Requirements

   The calculator applies the maximum allowable slope ratio for the soil type to determine the required top width, slope distance, and total excavation volume including the sloped sides.

4. Review Cross-Section Diagram

   An SVG cross-section shows the trench profile with slope angles, dimensions, and the additional material that must be excavated beyond the vertical trench walls. Compare sloping versus shoring costs.

5. Document the Decision

   Record the soil classification, slope ratio used, and competent person's name on the excavation permit. OSHA requires daily inspections and re-evaluation after rain or freeze/thaw events.

Built For

• Competent persons determining required slope angles before starting utility trench excavations deeper than 5 feet
• Estimators calculating extra excavation volume and spoil-hauling costs for sloped trenches versus shoring rental
• Site supervisors comparing Type B (1:1) versus Type C (1.5:1) top widths against available right-of-way on urban projects
• Civil contractors figuring total cubic yards to move for a 200-foot sewer line trench at 10-foot depth in Type B soil
• Safety directors preparing excavation permits with documented soil type, slope ratio, and competent person sign-off
• Municipal water department crews sizing open cuts for water main replacement in varying soil conditions along a route
• OSHA compliance auditors verifying that actual field slopes match the required ratios for the classified soil type

Features & Capabilities

OSHA Soil Type Selection

Choose from Type A (3/4:1), Type B (1:1), Type C (1.5:1), or Stable Rock (vertical). Displays the slope angle in degrees alongside the ratio.

Top Width Calculation

Calculates the required top width based on depth and slope ratio. Shows how much wider the cut must be compared to the bottom width.

Excavation Volume Output

Computes total cubic yards including the sloped sides so you can estimate hauling and disposal costs for the extra material.

SVG Cross-Section Diagram

Generates a visual cross-section showing the trench profile with labeled dimensions, slope angle, and bottom width.

Benching Option

Shows benching configurations for Type A and Type B soils as an alternative to simple sloping. Not allowed in Type C.

PDF Export

Export trench diagrams and calculations as a branded PDF for excavation permits and competent person documentation.

Assumptions

• Maximum allowable slopes per OSHA 29 CFR 1926.652 Appendix B: Type A = 3/4:1 (53 degrees), Type B = 1:1 (45 degrees), Type C = 1.5:1 (34 degrees)
• Stable Rock permits vertical excavation with no sloping requirement per OSHA Appendix B
• Soil classification performed per OSHA Appendix A using visual and manual tests (thumb penetration, pocket penetrometer, or unconfined compression)
• Trench profile assumes uniform soil type from surface to bottom — layered soils use the weakest layer classification
• Excavation volume calculation uses a trapezoidal cross-section with uniform slope on both sides
• Benching configurations follow OSHA Appendix B: allowed for Type A (4-ft maximum bench height) and Type B (4-ft maximum bench height), prohibited for Type C
• Trenches 5 feet or deeper require a protective system unless excavation is entirely in stable rock

Limitations

• Does not account for surcharge loads (spoil piles, construction equipment, traffic) near the trench edge, which require additional setback or flatter slopes
• Groundwater, seepage, and dewatering conditions change soil classification — saturated soil defaults to Type C regardless of dry classification
• Does not model mixed soil layers where different strata require different slope angles within the same excavation
• Cannot replace daily field inspections by a competent person, which are required by OSHA after rain, freeze/thaw, and vibration events
• Trenches deeper than 20 feet require a registered professional engineer's design — this calculator provides OSHA tabulated data only
• Adjacent structures, underground utilities, and vibration from nearby traffic may require flatter slopes than the OSHA maximum allowable values

References

• OSHA 29 CFR 1926.652 — Requirements for Protective Systems in Excavations
• OSHA 29 CFR 1926.652 Appendix A — Soil Classification (visual and manual test procedures)
• OSHA 29 CFR 1926.652 Appendix B — Sloping and Benching (maximum allowable slopes by soil type)
• OSHA 29 CFR 1926.651 — Specific Excavation Requirements (competent person, inspections, access)
• OSHA Publication 2226 — Excavation: Hazard Recognition in Trenching and Shoring
• NIOSH Workplace Solutions — Preventing Worker Deaths and Injuries from Excavation Cave-Ins (Publication No. 2015-108)

Frequently Asked Questions