An excavation is 8 feet deep in Type B soil. A worker reports water seepage at the 6-foot level. What is the required slope ratio for this condition?
Correct Answer
C) 1:1
When water is present in Type B soil, OSHA requires the slope to be cut back to 1:1 (45 degrees) rather than the normal 3/4:1 for dry Type B soil.
Why This Is the Correct Answer
OSHA 29 CFR 1926 Subpart P governs excavation safety. Type B soil normally allows a 3/4:1 slope (run:rise). However, when water seepage is present, the soil's cohesive strength is compromised — water reduces friction between soil particles and can trigger sudden collapse. OSHA mandates that wet or water-saturated Type B soil be treated as if it were Type C, requiring the more protective 1:1 slope (45-degree angle). This adjustment directly addresses the increased cave-in risk from water infiltration.
Why the Other Options Are Wrong
Option A: 1.5:1
1.5:1 is the required slope for Type C soil (the weakest classification) in dry conditions. While more conservative, this slope is not the specific requirement triggered by water in Type B soil. The OSHA standard for Type B with water is 1:1, not the Type C standard.
Option B: 3/4:1
3/4:1 is the standard slope for Type B soil in dry conditions. Once water seepage is reported at 6 feet, the dry-soil classification no longer applies. Maintaining 3/4:1 in wet conditions would be a serious safety violation because water dramatically reduces soil stability.
Option D: 1/2:1
1/2:1 is the permissible slope for Type A soil — the strongest, most stable classification. Applying the Type A slope to wet Type B soil would be extremely dangerous. Water seepage is a downgrading condition, not an upgrading one.
Memory Technique
Water in B = treat it like C in slope steepness: go to 1:1. 'When B gets wet, go straight (45°).'
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