Recognizing Soil Distress in Excavations
The Problem
Excavation work is one of the most hazardous activities in the construction industry. One of the leading causes of fatalities is trench collapse due to soil movement or failure. Even when protective systems are in place, signs of soil distress can develop—and if they’re not recognised and addressed early, the consequences can be deadly. Every worker must know how to identify these warning signs and report them to the Competent Person immediately. Today, we’ll cover how to spot soil distress and the actions required to keep the team safe.
Identify the Hazards
Tension Cracks: These appear near the top edge of the trench, usually between halfway and three-quarters of the depth. They signal soil is starting to fail.
Bulging and Subsidence:
- Bulging: The trench wall pushes outward.
- Subsidence: The top edge of the excavation sinks below the surrounding surface.
Both indicate that the soil is shifting and could collapse.
Heaving: Soil at the bottom of the trench rises upward, suggesting pressure is building below the excavation—this may push loose soil into the trench.
Safety Practices and Preventative Measures
1. Tension Cracks
What to Look For: Cracks running along the top edge of the trench.
Why It’s Important: Indicates soil is under strain and may collapse inward.
Action to Take:
- Notify the Competent Person immediately.
- Stop work until the slope or protective system has been evaluated and adjusted if needed.
2. Bulging and Subsidence
What to Look For:
- Walls pushing outward (bulging).
- Edges of the excavation sinking below surrounding ground level (subsidence).
Why It’s Important: These are signs that the soil is moving and unstable, raising the risk of collapse.
Action to Take:
- Report it to the Competent Person right away.
- Be prepared to adjust shoring or slope angles as directed.
3. Heaving
What to Look For: Soil lifting at the base of the trench or floor of the excavation.
Why It’s Important: This suggests pressure is forcing soil upward, which can cause sudden failure.
Action to Take:
- Alert the Competent Person immediately.
Stop work until protective systems are reassessed and adjusted as needed.
Real-Life Case or Scenario
In a recent trenching incident, workers noticed small tension cracks at the edge of the excavation but did not report them. Later that day, the trench collapsed, trapping a worker under tonnes of soil. Although emergency services responded quickly, the worker sustained severe injuries. This tragic event could have been avoided if early warning signs had been reported and acted on.
Employee Responsibilities
- Stay alert for signs of soil distress like cracks, bulging, subsidence, or heaving.
- Report all signs of instability to the Competent Person immediately.
- Do not enter any trench that appears unsafe or unstable.
- Follow all safety instructions and never ignore unusual ground conditions.
Employer Responsibilities
- Ensure protective systems are in place for all excavations deeper than 1.5 metres.
- Appoint a Competent Person to regularly monitor soil conditions and trench safety.
- Train workers to identify, report, and respond to signs of soil distress.
Discussion & Questions
- “Have you ever noticed signs of soil movement or collapse on site? What did you do?”
- “What can we do as a team to make sure soil changes are recognised and reported straight away?”
Encourage the team to share experiences and ask any questions to ensure everyone understands what to look for.
Commitment/Action Plan
Let’s commit to this safety principle: If you see signs of soil distress—no matter how small—report it immediately. Acting early can prevent serious injury or even save a life.
Wrap-Up
Excavation safety is a shared responsibility. By staying alert, recognising early warning signs of soil movement, and working closely with the Competent Person, we can prevent trench collapses. Thank you for prioritising health and safety—and remember: speak up if something looks wrong. Your observation could save a life.
Standards Overview
Under the Health and Safety at Work Act 2015 (HSWA) and WorkSafe NZ excavation safety guidelines, PCBUs must:
- Use protective systems (e.g., trench shields or shoring) in excavations deeper than 1.5 metres.
- Assign a Competent Person to monitor soil conditions and inspect trenches regularly.
- Ensure workers are trained to identify and report soil instability and hazards.
- Stop work immediately if any signs of distress are identified until corrective actions are taken.
Disclaimer
These toolbox talks are provided for informational and educational purposes only and are not a substitute for professional legal, health and safety, or regulatory advice.
The content reflects recognised best practices and general industry standards as at the date of publication. However, it may not be applicable to all workplace environments or specific operational contexts.
It is the responsibility of the Person Conducting a Business or Undertaking (PCBU), as well as officers, workers, and other duty holders under the Health and Safety at Work Act 2015 (HSWA), to ensure compliance with all relevant laws, regulations, and WorkSafe New Zealand guidance.
The authors, presenters, and distributors of this toolbox talk disclaim all liability for any loss, damage, or injury arising from the use or reliance on the information provided. Users should seek advice from a suitably qualified health and safety professional or legal advisor for guidance tailored to their specific circumstances.
Always follow your organisation’s policies, procedures, and safe work practices to manage risks and maintain a safe and healthy workplace.
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