Excavation Safety Flashcards

What type of excavation support system uses hydraulic rams to hold apart two vertical panels placed against the trench walls?

Answer: Hydraulic shoring frames (also known as hydraulic waling frames or speed shores)

Hydraulic shoring frames use adjustable hydraulic rams between two vertical plates or waling beams to support trench sides. They are quick to install (hence 'speed shores'), adjustable to various trench widths, and can be installed from outside the trench, reducing the risk to operatives. Under CDM Regulations 2015, the competent person specifies the appropriate support system.

What documentation must the competent person produce after each statutory inspection of an excavation?

Answer: A written inspection report within 24 hours, recording the excavation condition, any defects found, and actions required — kept on site for at least 3 months

Under CDM Regulations 2015 Schedule 3, the competent person must produce a written report of every excavation inspection. The report must be completed before the end of the working period during which the inspection was made, include details of any defects and remedial actions, and be kept on site and available for inspection for at least 3 months.

What method is used to determine the depth of a buried service detected by a CAT scanner?

Answer: By using the depth estimation feature on the CAT, which calculates depth based on signal gradient, and confirming with hand-dug trial holes

Modern CAT scanners have a depth estimation feature that calculates the approximate depth of a detected service based on the signal gradient. However, HSE guidance HSG47 emphasises that this is an estimate only and must always be confirmed by hand-dug trial holes before mechanical excavation. The depth reading can be affected by nearby services, ground conditions, and signal interference.

What is the legal requirement for providing welfare facilities near excavation work sites?

Answer: Under CDM Regulations 2015, welfare facilities including toilets, washing facilities, drinking water, rest areas, and changing rooms must be provided within a reasonable distance of all work areas including excavations

CDM Regulations 2015 Schedule 2 requires welfare facilities including sanitary conveniences, washing stations, drinking water, rest facilities, and changing rooms to be provided for all construction workers. These must be readily accessible from all work areas. For excavation workers who may be muddy and wet, adequate washing and changing facilities are particularly important.

What emergency rescue equipment should be available at the site of a deep excavation?

Answer: A rescue plan including trained rescue personnel, retrieval equipment (harnesses and winch systems), first aid equipment, and means of communication

Under CDM Regulations 2015 and the Management of Health and Safety at Work Regulations 1999, a rescue plan must be in place before deep excavation work begins. This includes trained rescue personnel on site, suitable retrieval equipment, first aid provisions, means of raising the alarm, and communication systems. Relying solely on emergency services is not acceptable as response times may be too long.

What is the purpose of installing piezometers around a large excavation site?

Answer: To monitor groundwater pressure (pore water pressure) in the soil, providing early warning of changes that could affect the stability of the excavation

Piezometers measure pore water pressure in the ground surrounding an excavation. Rising water pressure reduces the effective stress in the soil, increasing the risk of instability and collapse. Continuous piezometer monitoring provides early warning of dangerous changes, allowing preventive action. This is often required as part of the monitoring scheme specified under CDM Regulations 2015 for major excavations.