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.
