The inspection must be conducted by a person who has completed the Excavation and Trenching Awareness Training (linked below) as a minimum.

Inspections must be conducted more frequently if a rainfall event or any other event could impact ground stability or introduce further hazards.

If any indication of ground movement is identified (e.g. cracks, undercutting, bulging etc.) or any impacts to adjacent structures are identified, the integrity of the excavation should be reviewed before any work in that area commences.

Ground conditions encountered in excavations can generally be categorised as one of 3 types:

• Hard, compact soil
• Soil liable to crack or crumble, and
• Loose or running material

Hard, compact soil is often the most hazardous as the face of the excavation can look solid, which can lead in more risks being taken.

With loose or running material, it is obvious that controls are needed from the start and more precautions are taken to prevent collapse.

The stability of any excavated face depends on the strength of the soil in the face being greater at all times than the stresses it is subjected to.

The following situations all increase soil stresses in an excavated face, which may lead to failure:

• Deep cuts and steep slopes
• Loads placed near the excavation face inside the zone of influence
• Shock and vibration
• Water pressure from groundwater
• Soil saturation

Those inspecting the excavation should look out for:

• Fissures or cracks on the excavation face
• Slumping of material, soil or rock
• Bulging or heaving of material at the bottom of the excavation wall
• Sinking at the edge of the trench
• Pebbles of clumps of dirt rolling down the excavation face

Types of ground collapse:

Excavation Safety Guide. New Zealand