Excavation and Trenching Safety Flashcards
6 cards from real STSC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Excavation and Trenching Safety flashcards as text
An excavation competent person is classifying soil at a trench site. A fist-sized sample of moist soil crumbles when squeezed in the hand. What soil type does this indicate?
Answer: Type C
Soil that crumbles or falls apart when squeezed — rather than holding a formed shape — is cohesionless (granular or poorly cohesive) and should be classified as Type C, the least stable classification.
What is 'benching' as a method of excavation protection, and which soil type does NOT permit it?
Answer: Benching creates step-like horizontal cuts in trench walls — not permitted in Type C soil
Benching creates horizontal steps in the trench wall, allowing the soil above each step to provide support. It is NOT permitted in Type C soil because Type C is too unstable to maintain bench faces.
A contractor decides to use a timber shoring system in a trench. Who must design the shoring system?
Answer: A tabulated data system approved by a registered professional engineer, or a custom design by a registered PE
Under OSHA Appendix C to Subpart P, timber shoring must either follow tabulated data (pre-engineered tables by a registered PE) or be custom-designed by a registered professional engineer for the specific project conditions.
What is the minimum distance that heavy equipment must maintain from the edge of an excavation to prevent excessive surcharge loading on trench walls?
Answer: Determined by the competent person based on soil type, depth, and equipment weight
OSHA does not specify a fixed minimum distance for heavy equipment — the competent person must assess the surcharge effect based on equipment weight, soil type, trench depth, and protective system design.
Which of the following is a recognized method for controlling water accumulation in an active excavation?
Answer: Installing dewatering equipment (pumps, well points, or drainage ditches)
Dewatering using pumps, well points, or drainage ditches is the recognized engineering control for controlling water accumulation in excavations — maintaining dry working conditions and preventing hydrostatic pressure buildup in trench walls.
When an excavation is made next to an existing building foundation, what additional hazard must the competent person evaluate?
Answer: Undermining of the existing foundation and potential building collapse
Excavating adjacent to existing foundations can undermine their bearing capacity, causing the foundation to settle, shift, or fail — potentially collapsing the adjacent structure and burying workers in the trench.