Calculate required cut slope setback distance and maximum slope ratio by OSHA soil classification (Type A, B, C, Rock). Uses OSHA 29 CFR 1926 Subpart P Appendix B tables. Includes compliance note and OSHA soil classification reference.
Monitor excavation slope stability and depth with a Leica Disto laser distance meter or rotary laser.
Shop Express Tools →OSHA Appendix A to Subpart P defines acceptable soil classification methods. A competent person must use at least one visual test and one manual test:
Sloping is one of three protective systems allowed by OSHA for excavations deeper than 5 feet. Shoring uses wood, aluminum hydraulic shores, or steel sheet piling to physically support the excavation walls — required in tight urban sites where sloping would encroach on adjacent structures. Trench boxes (shielding) protect workers by creating a steel or aluminum box that workers stay inside, without necessarily preventing the walls from caving above the box top. Shoring and shielding systems must be appropriate for the excavation depth and soil conditions — consult the manufacturer's tabulated data or a licensed engineer.
OSHA 29 CFR 1926.651(j)(2) requires that excavated material (spoil) be kept at least 2 feet from the edge of the excavation. This minimum clearance is a floor requirement — the actual required setback depends on soil type, excavation depth, and the surcharge pressure from the spoil pile itself. Heavy spoil piles adjacent to the excavation increase lateral pressure on the cut face and may require greater setback than the 2-foot minimum. A competent person must evaluate spoil pile proximity as part of daily inspection.
OSHA 29 CFR 1926 Subpart P classifies soils into three types for excavation safety: Type A is the most stable (hard clay, hardpan, cemented soils — unconfined compressive strength 1.5 tsf or greater); Type B is intermediate (silt, sandy loam, fissured Type A — 0.5 to 1.5 tsf); and Type C is the least stable (sand, gravel, saturated soil, submerged — less than 0.5 tsf). Rock is a separate category. A competent person must classify soil on-site using thumb tests, pocket penetrometer, or laboratory testing.
OSHA 29 CFR 1926 Appendix B sets maximum slopes for simple slope systems: Type A — 3/4H:1V (53 degrees from horizontal); Type B — 1H:1V (45 degrees); Type C — 1.5H:1V (34 degrees); Stable Rock — nearly vertical, typically 1/4H:1V per guidance. These slopes apply to simple cut excavations. OSHA also allows benching, shoring, and trench box systems as alternatives to sloping.
OSHA requires a protective system (sloping, shoring, or shielding) for any excavation deeper than 5 feet in which an employee may be exposed to cave-in risk. For excavations 20 feet or deeper, the protective system must be designed by a registered professional engineer. Between 5 and 20 feet, a competent person may use sloping tables from OSHA Appendix B if they can classify the soil. Excavations less than 5 feet may require protection if a competent person determines cave-in hazard exists.
A competent person is defined by OSHA as someone capable of identifying existing and predictable hazards, authorized to take corrective action, and trained in soil classification and excavation safety. Competent persons must inspect excavations daily and after any hazard-changing event (rain, freeze-thaw, vibration from equipment). They perform soil classification using visual and manual tests including the thumb penetration test, dry strength test, plasticity test, and observation for fissures or layering.
This calculator provides the OSHA slope ratios from Appendix B as a field reference tool. It is not a substitute for on-site soil classification by a competent person. Soil conditions change daily — after rain, adjacent vibration from equipment, or frost thaw — and must be re-evaluated by a competent person. Do not use this calculator as the sole basis for excavation safety decisions. Always consult a qualified competent person and, for deep excavations, a licensed geotechnical engineer.