Trench Benching Chart

Benching per OSHA 1926 Subpart P App B — the bench dimensions come from the standard's official figures, and the headline is what's absent: Type C has no bench configuration at all. All benching lives inside the overall slope envelope, to 20 ft, with the competent person's classification deciding which row applies. State plans can be stricter.

Benching by soil type

1926 Subpart P App B
Bench permissions and dimensions per the Appendix B figures. Every bench stack must stay inside the soil type's overall maximum-slope envelope.
Soil typeBenching permitted?Dimensions
Type AYesBottom bench 4 ft max; upper benches 5 ft max; overall envelope ¾:1
Type BCohesive soil ONLY (verbatim on the OSHA figures)All benches 4 ft max; overall envelope 1:1
Type CNO — no bench configuration exists in Appendix B—
The “cohesive soil only” restriction on Type B is printed verbatim on the OSHA figures. Layered ground: classify the system by its weakest layer; a more stable lower layer may be sloped at its own steeper angle — a weaker layer below pulls the whole cut to the weaker slope.

Bench or slope or box?

Benching saves width versus a full slope in strong soil — a benched Type A cut stands nearer vertical at the faces while honoring the ¾:1 envelope — but it costs excavation time and demands soil that holds a face. The decision usually resolves by real estate: in a street or near footings there is no room to slope OR bench, and the answer is a box or shoring. Start from the classification, check the slope chart, and let the site pick the system.

Common questions

Can you bench Type C soil?

No. Appendix B contains no bench configuration for Type C — granular soil won't hold a bench face, so the options are the full 1½:1 slope or a supported/shielded vertical section. Crews sometimes cut "steps" in sandy soil for convenience; on a Type C classification that is an unprotected excavation, not a protective system.

What are the bench dimensions for Type A soil?

From the official OSHA figures: a simple bench up to 4 ft; in multiple-bench cuts, the bottom bench maxes at 4 ft and each bench above it at 5 ft — all inside the overall ¾:1 envelope, to 20 ft total depth. The envelope is the real rule: the bench corners must not poke outside the line a plain ¾:1 slope would cut.

Why is Type B benching limited to cohesive soil?

Because Type B includes granular cohesionless soils (angular gravel, silt, sandy loam) that hold a slope but not a vertical bench face. The OSHA figures print the restriction verbatim — "This bench allowed in cohesive soil only" — so a Type B classification alone isn't enough; the competent person also has to call it cohesive.

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