When shielding or shoring is not used, the excavation must be sloped or benched to a safe angle that prevents soil failure. The required slope depends entirely on the soil type — and getting the soil classification wrong means the slope that looks adequate can collapse without warning. These numbers are not suggestions; they are engineered requirements based on soil failure mechanics.

• Type A (most stable — stiff clay): Maximum slope ¾:1 (horizontal to vertical) = 53° from horizontal. This is steep and requires rigorous soil testing to confirm Type A classification
• Type B (moderate stability — medium clay, sandy gravel, fissured rock): Maximum slope 1:1 = 45° from horizontal. The most common classification on NYC sites
• Type C (least stable — granular soil, submerged soil, previously disturbed): Maximum slope 1.5:1 = 34° from horizontal. Any soil in the presence of water defaults to Type C at minimum
• Reclassification: if conditions change (rain, vibration, seeping water), the slope must be reevaluated — Type A can degrade to Type B or C within a shift

• Benching (stepped excavation walls) may only be used in Type A and Type B soil — never in Type C
• Each bench must have a minimum 4-foot horizontal dimension and a maximum 4-foot vertical rise per bench
• The maximum depth of a simple bench excavation: 20 feet with a single bench step
• No benching permitted below the water table regardless of soil classification