A trench excavation is 15 feet deep in Type C soil with workers entering daily. Which protection method is most appropriate?
Correct Answer
C) Hydraulic shoring system
At 15 feet deep in Type C soil, sloping would require excessive space and benching becomes impractical. A properly designed shoring system (hydraulic, pneumatic, or timber) is the most practical protection method for deep excavations.
Why This Is the Correct Answer
At 15 feet deep in Type C soil (the least stable soil type), a hydraulic shoring system is the most practical and effective protection method. Simple sloping at the required 1½:1 ratio would require an enormous excavation area (22.5 feet back from each side), making it impractical in most construction scenarios. Shoring systems provide maximum protection while allowing efficient work in confined spaces, and they can be easily adjusted as excavation progresses.
Why the Other Options Are Wrong
Option A: No protection needed if workers stay near the ladder
Simple sloping at 1½:1 for a 15-foot deep trench in Type C soil would require sloping back 22.5 feet from each side of the trench, creating a massive excavation area that is typically impractical and cost-prohibitive for most construction sites.
Option B: Benching with 4-foot maximum bench height
While benching is allowed in Type C soil, at 15 feet deep it becomes impractical and less safe than shoring. The multiple bench levels required would create complex geometry and potential instability issues compared to a properly designed shoring system.
Memory Technique
Deep = Shoring. When trenches get deep (especially 15+ feet), sloping becomes 'slope-less' practical, so shore it up with shoring systems.
Reference Hint
OSHA Construction Standards 29 CFR 1926 Subpart P - Excavations, specifically sections on protective systems and soil classification
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