CHST - Construction Health and Safety Technician Excavation and Trenching Safety Questions and Answers Flashcards

A contractor uses timber shoring in a 9-foot deep trench. OSHA Appendix C tables indicate the uprights should be spaced at a maximum of 8 feet apart. The contractor spaces them 10 feet apart. What is the violation?

Answer: Failure to comply with tabulated data, which is a violation of 29 CFR 1926.652

Tabulated data in OSHA Appendix C must be followed as written; exceeding the maximum spacing undermines the engineered protection and violates 29 CFR 1926.652.

What term describes the failure of a large mass of soil on the side of an excavation that slides in and rotates downward due to the weight of the soil above?

Answer: Rotational slide (slump failure)

A rotational slide (slump failure) occurs when a curved failure plane develops and a mass of soil rotates and slides into the excavation.

Which of the following correctly describes 'heave' in the context of excavation hazards?

Answer: Upward movement of the trench bottom caused by soil pressure differential

Heave is an upward bulging of the trench bottom caused by the weight of soil on the sides exceeding the bearing capacity of the material below the trench floor.

Under OSHA standards, what action is required when a water accumulation hazard exists in a trench?

Answer: Workers must not enter until water is controlled and a competent person has assessed the situation

OSHA 29 CFR 1926.651(h) prohibits workers from entering excavations with accumulated water unless water control measures are taken and a competent person approves re-entry.

Which type of shoring uses steel plates driven into the ground before excavation begins to prevent soil movement?

Answer: Sheet piling

Sheet piling consists of interlocking steel sheets driven vertically into the ground prior to excavation to retain soil and groundwater.

A competent person must have which TWO characteristics according to OSHA's definition?

Answer: Knowledge to identify existing and predictable hazards AND authority to take corrective action

OSHA defines a competent person as one who can identify hazardous conditions and has the authority to eliminate them promptly (29 CFR 1926.32(f)).

Which scenario most accurately describes a 'fissured' soil condition that affects soil classification?

Answer: Soil with cracks or tension fractures visible in the trench wall

Fissured soil contains visible cracks or fractures that indicate internal failure planes, reducing its cohesive strength and requiring reclassification to Type B or C.