OSHA Soil Classification & Sloping Chart

Per OSHA Table B-1 (29 CFR 1926 Subpart P, Appendix B), for excavations less than 20 feet deep: Stable Rock is vertical (90°), Type A is 3/4:1 (53°), Type B is 1:1 (45°), and Type C is 1-1/2:1 (34°). A short-term (24 hours or less) slope of 1/2:1 (63°) is allowed in Type A soil only when the excavation is 12 feet deep or less.

Type A is cohesive soil with an unconfined compressive strength of 1.5 tons per square foot (144 kPa) or greater. Type B cohesive soil is greater than 0.5 tsf but less than 1.5 tsf; Type C cohesive soil is 0.5 tsf (48 kPa) or less. Cemented soils such as caliche and hardpan are also Type A — but no soil is Type A if it is fissured, subject to vibration, previously disturbed, or in a layered system sloping into the excavation at 4H:1V or greater.

Under 29 CFR 1926.652(a)(1), every employee in an excavation must be protected from cave-ins by an adequate protective system (sloping, benching, shoring, or shielding) unless the excavation is entirely in stable rock, or is less than 5 feet deep and a competent person finds no indication of a potential cave-in. Excavations deeper than 20 feet require a protective system designed by a registered professional engineer.

Yes. OSHA 1926.652(b)(1) (Option 1) allows sloping at no steeper than 1-1/2 horizontal to 1 vertical (34°) — the Type C slope — without classifying the soil. To use the steeper Type A or B slopes you must classify the soil per Appendix A (Option 2).

A competent person. Appendix A requires each soil and rock deposit to be classified as Stable Rock, Type A, B, or C based on at least one visual and at least one manual test (e.g. thumb penetration, pocket penetrometer, plasticity, dry strength, drying test), and reclassified whenever conditions change — for example after rain or when water starts seeping.