Practice Question: Sloping Requirements for a Utility Excavation

NCEES Civil PE Specification VIII.E.: Safety

Problem

You are planning an excavation to access a utility line. A competent person has identified soil at the excavation site as Type C. Given a horizontal distance of 12 feet from edge of shoring to edge of an existing roadway, what is the maximum vertical distance Y that can be considered without compromising the excavation?

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Solution

Answer: C) 8 ft

OSHA 1926 Subpart P Table B-1 identifies the maximum allowable slope for Type C soil as 1 ½:1 (H:V).
Accordingly:
$$ Y=12\ ft\ast1/1.5=8\ ft $$
Note that the total excavation depth is:
$$ 8\ ft+5\ ft=13\ ft<20\ ft $$
If the total depth was greater than 20 feet, an engineered shoring system would be required.