EXC/Support Systems/TBT-EXC-037
Excavation Near Existing Structures
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Excavation Near Existing Structures
Excavating near existing buildings, retaining walls, and buried structures can undermine their foundations and cause settlement, cracking, or collapse. The closer and deeper the excavation, the greater the risk. Ground movement from excavation has caused partial building collapses and fatal injuries. This talk covers the precautions needed when excavating close to existing structures on UK construction sites.
Key Hazards
Settlement or collapse of adjacent buildings from undermined foundations
Retaining wall failure from loss of passive earth pressure during excavation
Cracking and structural damage to neighbouring properties from ground movement
Buried foundation obstructions encountered unexpectedly during digging
Control Measures
- Review structural and geotechnical reports to understand the existing foundations before excavation.
- Install monitoring points on adjacent structures to detect movement before damage occurs.
- Use sheet piling or shoring to retain the ground and protect existing foundations from disturbance.
- Excavate in short sections to limit the length of unsupported ground at any time.
- Set trigger levels for movement monitoring and define stop-work actions if they are reached.
- Brief the excavation team on the proximity of existing structures and the required precautions.
- Photograph and record the condition of adjacent buildings before excavation begins.
- Notify building owners and occupants before starting excavation near their property.
- Ensure a competent person inspects the excavation face daily for signs of ground movement.
Remember
- Review structural and geotechnical reports before excavating near any existing structure
- Install monitoring points on adjacent structures and set trigger levels for movement
- Excavate in short sections to limit the length of unsupported ground at any time
- Photograph adjacent buildings before work starts to record their pre-existing condition
- Stop work immediately if monitoring shows movement approaching the trigger level
Applicable Legislation: CDM 2015 · Party Wall etc. Act 1996 · BS 5975:2019 (Temporary Works) · MHSWR 1999
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