CITB Excavation and Groundworks 1 — Questions and Answers
Question 1: What is the minimum safe distance from the edge of an excavation that spoil should be placed to prevent collapse?
- 0.5 meters
- 1 meter (Correct answer)
- 2 meters
- 3 meters
Correct answer: 1 meter
Spoil and materials must be kept at least 1 meter from the edge of an excavation to reduce surcharge loading that could cause the sides to collapse.
Question 2: Which document must be completed before any excavation work begins near underground services?
- Risk assessment only
- Method statement only
- Permit to dig (Correct answer)
- Site induction record
Correct answer: Permit to dig
A permit to dig is required before excavating near underground services to ensure all utilities have been identified, located, and safe digging procedures are followed.
Question 3: What is the primary purpose of shoring in an excavation?
- To drain water from the trench
- To support the sides and prevent collapse (Correct answer)
- To mark the excavation boundary
- To compact the soil at the base
Correct answer: To support the sides and prevent collapse
Shoring provides lateral support to the sides of an excavation to prevent soil movement and collapse, protecting workers inside the trench.
Question 4: Which utility cable color in the UK indicates a high-voltage electricity supply?
- Yellow
- Blue
- Black
- Red (Correct answer)
Correct answer: Red
High-voltage electricity cables in the UK are traditionally color-coded red, distinguishing them from lower-voltage distribution cables.
Question 5: What method is used to safely locate buried services before excavation?
- Probing with a metal rod
- Using a cable avoidance tool (CAT) (Correct answer)
- Digging trial pits only
- Reviewing site drawings only
Correct answer: Using a cable avoidance tool (CAT)
A cable avoidance tool (CAT) uses electromagnetic detection to locate buried services and should be used alongside signal generators and site drawings before any excavation.
Question 6: At what depth does an excavation generally require a formal inspection by a competent person?
- More than 1 meter
- More than 1.2 meters
- More than 1.5 meters
- More than 2 meters (Correct answer)
Correct answer: More than 2 meters
Under the Construction (Design and Management) Regulations, excavations over 2 meters deep require a formal inspection by a competent person at the start of each shift and after any event that may have affected stability.
Question 7: Which type of soil is MOST likely to be self-supporting and less prone to collapse in shallow excavations?
- Loose sand
- Wet clay
- Firm cohesive clay (Correct answer)
- Made ground
Correct answer: Firm cohesive clay
Firm cohesive clay has natural shear strength that allows it to stand unsupported for short periods in shallow excavations, unlike granular or waterlogged soils.
CITB Excavation and Groundworks 1
What is the minimum safe distance from the edge of an excavation that spoil should be placed to prevent collapse?