CITB Specialists Excavation and Groundwork Safety 2 — Questions and Answers
Question 1: What does the 'angle of repose' refer to in specialist excavation work?
- The angle at which an excavator boom should be positioned
- The steepest angle at which soil or loose material can be stacked without sliding (Correct answer)
- The correct angle for installing ladder access
- The angle of the trench support bracing
Correct answer: The steepest angle at which soil or loose material can be stacked without sliding
The angle of repose is the maximum angle at which soil or granular material remains stable without slipping. It varies by soil type — sand may be 30-35 degrees, while clay can be steeper when dry but much shallower when wet. Understanding this is critical for determining whether battering back the sides is sufficient or if sheet piling is needed.
Question 2: A specialist contractor encounters groundwater ingress during deep excavation. What is the most appropriate response?
- Continue digging as the water will drain away
- Implement a dewatering system (wellpoint or sump pumping) and assess the effect on surrounding structures and services (Correct answer)
- Add more support to the trench and continue
- Abandon the excavation and relocate
Correct answer: Implement a dewatering system (wellpoint or sump pumping) and assess the effect on surrounding structures and services
Groundwater ingress requires controlled dewatering using appropriate methods (wellpoint dewatering, sump pumps). Crucially, the effect of lowering the water table on adjacent structures, services, and contaminated land must be assessed, as dewatering can cause settlement. Discharge of pumped water must comply with Environment Agency requirements.
Question 3: What type of access and egress must be provided for specialist workers in excavations deeper than 1.2 metres?
- Workers can climb the trench support system
- A secured ladder extending at least 1 metre above the excavation edge, positioned within reasonable reach of all work positions (Correct answer)
- A rope for climbing in and out
- Steps cut into the trench wall
Correct answer: A secured ladder extending at least 1 metre above the excavation edge, positioned within reasonable reach of all work positions
Safe access and egress must be provided, typically by a secured ladder extending at least 1 metre above the top of the excavation. Ladders must be positioned so that workers do not have to travel more than a reasonable distance (typically 25 metres) laterally along the excavation to reach one. Steps cut into soil are not acceptable as they undermine the trench wall.
Question 4: Under UK environmental regulations, what must a specialist contractor do if contaminated soil is discovered during excavation?
- Mix it with clean soil and reuse it on site
- Stop work, isolate the area, test the material, and dispose of it at a licensed facility in accordance with waste regulations (Correct answer)
- Remove it from site and dump it in a skip
- Cover it with a membrane and continue working
Correct answer: Stop work, isolate the area, test the material, and dispose of it at a licensed facility in accordance with waste regulations
Contaminated soil is classified as controlled waste. The contractor must stop work, prevent further spread, characterise the contamination through testing, and arrange disposal at a suitably licensed facility. Duty of care waste transfer notes must be completed. Mixing contaminated soil with clean soil is illegal under the Environmental Protection Act 1990.
Question 5: What is the purpose of a 'permit to dig' system used by specialist groundwork contractors?
- To obtain planning permission for the excavation
- To formally confirm that underground services have been located and marked, safe digging methods agreed, and specific precautions are in place before digging begins (Correct answer)
- To allow the use of mechanical excavation equipment
- To confirm the soil type before excavation
Correct answer: To formally confirm that underground services have been located and marked, safe digging methods agreed, and specific precautions are in place before digging begins
A permit to dig is a formal management control document that confirms service drawings have been checked, detection equipment has been used, services have been marked on the ground, safe digging methods are specified (hand dig zones), and all relevant precautions are in place. It must be signed by the supervisor and reviewed if conditions change.
Question 6: A specialist excavation crew is working adjacent to a live highway. What additional control measures are required beyond standard excavation safety?
- High-visibility clothing is sufficient
- Traffic management plan, Chapter 8 compliant signage, vehicle restraint barriers, and a designated traffic management operative (Correct answer)
- A banksman to direct traffic
- Cones placed around the excavation
Correct answer: Traffic management plan, Chapter 8 compliant signage, vehicle restraint barriers, and a designated traffic management operative
Working adjacent to a live highway requires a traffic management plan designed to Chapter 8 of the Traffic Signs Manual, including advance warning signs, taper layouts, vehicle restraint systems (where impact risk exists), and designated traffic management operatives. The plan must be approved by the highway authority and reviewed regularly.
CITB Specialists Excavation and Groundwork Safety 2
What does the 'angle of repose' refer to in specialist excavation work?