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General Excavation

Hazard Related Topics

Including foundations, trenches, earthwork cuttings, basements/ shafts, pits and heritage sites.


When considering general excavations the designer should be aware of, and assess the risks from, the following principal hazards. It is important that, where these risks cannot be eliminated or reduced during the design process and they are perceived as 'significant risks', details of them are included in the Pre-Construction Information, for prospective principal contractors. The prospective principal contractors must outline the control measures proposed in respect of these 'significant hazards' in the construction phase plan. When a tender is accepted and the project reaches the construction phase the principal contractor must control the hazards and risks as outlined in his construction phase plan.

Some principal hazards and risks

  • Hazards associated with the collapse of the walls of an excavation or collapse caused by the undermining of adjacent structures
  • Falls from height into excavations
  • Falls of objects into excavations
  • Struck by plant or machinery
  • Health hazards caused by contaminated ground, toxic chemicals. asbestos, skin irritants etc.
  • Potential hazards of services such as buried electrical cables, gas pipelines or sewage and process effluents
  • Hazards of flooding, groundwater, methane etc.


  • Investigate site topography, ground conditions and slope stability.
  • What are the types and use of adjacent property and what are the length and location of any temporary roads and traffic routes to tip?
  • Where are existing services?

Some design options for hazard reduction

  • Design to avoid possibility of undermining adjacent structures
  • Consider location of hard routes and tip sites which have least impact on construction and the local community
  • Ensure ground investigation will detect local contamination
  • Consider de-watering methods to stabilise ground in low-lying waterlogged ground
  • Where there is limited working space consider excavations within piled supports
  • Consider shoring options for adjacent structures to maximise working space within site excavation
  • When considering bored pile side supports in contaminated ground plan for handling and disposal of spoil

See Also