A trench excavation is 14 feet deep in Type A soil. The contractor wants to use sloping instead of shoring. What is the maximum horizontal distance required from the top edge to achieve proper sloping under Cal/OSHA standards?
Correct Answer
C) 10.5 feet
For Type A soil, Cal/OSHA requires a 3:4 slope ratio. For a 14-foot deep trench: 14 × 0.75 = 10.5 feet horizontal distance.
Why This Is the Correct Answer
Cal/OSHA requires a ¾:1 (horizontal:vertical) slope ratio for Type A soil, meaning 0.75 feet of horizontal distance for every 1 foot of depth. For a 14-foot deep trench: 14 × 0.75 = 10.5 feet of horizontal setback from each wall edge. This is the least restrictive ratio because Type A is the strongest soil classification.
Why the Other Options Are Wrong
Option A: 14 feet
14 feet horizontal would represent a 1:1 ratio (1H:1V), which is the requirement for Type B soil — not Type A. Type A's stronger soil allows a steeper cut (less horizontal setback), making 14 feet overly conservative.
Option B: 21 feet
21 feet horizontal would represent a 1.5:1 ratio, which is required for Type C soil — the weakest, most unstable classification. Using this ratio for Type A soil would be unnecessarily wide and costly.
Option D: 7 feet
7 feet horizontal would represent a 0.5:1 ratio (½H:1V). This slope is steeper than allowed and would not provide adequate safety. Cal/OSHA does not permit ½:1 sloping for any excavation soil type under standard conditions.
Memory Technique
Remember the slope ratios with 'A, B, C = ¾, 1, 1½': A is best (less horizontal needed), C is worst (most horizontal needed). For the math: depth × ratio = horizontal. Type A: 14 × 0.75 = 10.5. If you remember A=0.75, the calculation follows.
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