General Contractor License Site Work and Excavation 5 — Questions and Answers
Question 1: What is the purpose of a 'soldier pile and lagging' wall system in excavation support?
- To pump groundwater from the excavation perimeter
- To retain soil using vertical steel H-piles with horizontal timber lagging inserted between them (Correct answer)
- To support temporary scaffolding around a deep excavation
- To anchor the shoring system to adjacent structures
Correct answer: To retain soil using vertical steel H-piles with horizontal timber lagging inserted between them
Soldier pile and lagging walls use driven or drilled H-piles as the primary structural element with timber, concrete, or steel lagging placed between them to retain the soil.
Question 2: A contractor must excavate within 18 inches of a gas line. What is the required excavation method?
- Proceed with a small hydraulic excavator equipped with a narrow bucket
- Use hand tools (hand digging) or hydrovac (vacuum excavation) only (Correct answer)
- Use a standard backhoe but at reduced speed
- Install a temporary protective sleeve over the pipe first, then excavate normally
Correct answer: Use hand tools (hand digging) or hydrovac (vacuum excavation) only
Within the tolerance zone (typically 18-24 inches) of a marked utility, only hand digging or hydrovac excavation is permitted to avoid striking the line.
Question 3: What does a 'percolation test' (perc test) measure on a construction site?
- The compressive strength of existing soil strata
- The rate at which soil absorbs water, used for septic system design (Correct answer)
- The groundwater elevation relative to the surface
- The pH level of soil to determine corrosion risk to metals
Correct answer: The rate at which soil absorbs water, used for septic system design
A percolation test measures how quickly water drains through soil, which is required data for designing septic systems and certain drainage features.
Question 4: Which method is used to verify that compacted fill meets specified density requirements?
- Visual inspection and probe rod test only
- Nuclear density gauge (Troxler gauge) or sand cone test compared to Proctor standard (Correct answer)
- Simply measuring the lift thickness during placement
- Using a standard penetration test (SPT) at each fill location
Correct answer: Nuclear density gauge (Troxler gauge) or sand cone test compared to Proctor standard
Nuclear density gauges and sand cone tests measure in-place density, which is compared to the maximum density from Proctor testing to verify compaction specification compliance.
Question 5: What is the term for the natural moisture content at which a particular soil can be most efficiently compacted?
- Saturation point
- Optimum moisture content (OMC) (Correct answer)
- Plastic limit
- Liquid limit
Correct answer: Optimum moisture content (OMC)
Optimum moisture content is the water content at which a given soil achieves its maximum dry density when compacted, as determined by the Proctor compaction test.
Question 6: During excavation, a worker notices tension cracks appearing parallel to the trench at ground level nearby. This indicates:
- Normal settlement from the weight of the spoil pile
- Imminent trench wall failure requiring immediate evacuation (Correct answer)
- The presence of underground utilities that need to be relocated
- That the soil type has changed from Type B to Type A
Correct answer: Imminent trench wall failure requiring immediate evacuation
Tension cracks parallel to a trench are a critical warning sign of impending wall failure; all workers must immediately exit the excavation and the area must be evaluated by a competent person.
Question 7: What is the function of a 'trench box' (trench shield) compared to shoring?
- It prevents groundwater infiltration into the trench
- It protects workers from cave-ins by providing a rigid box structure but does not support the trench walls (Correct answer)
- It replaces compaction requirements at the trench bottom
- It eliminates the need to call 811 before excavating
Correct answer: It protects workers from cave-ins by providing a rigid box structure but does not support the trench walls
A trench box shields workers inside it from cave-ins but does not prevent the walls from moving — it is a protective system, not a support system like hydraulic shoring.
General Contractor License Site Work and Excavation 5
What is the purpose of a 'soldier pile and lagging' wall system in excavation support?