GRW/Bulk Earthworks/TBT-GRW-008

Slope Stability Awareness

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Slope Stability Awareness

Toolbox Talk Record

Ref: TBT-GRW-008  |  Issue: 1  |  Date: March 2026
PresenterProject
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What?

  • Slope failures in cuttings, embankments, and stockpiles cause crushing fatalities.
  • Stability depends on soil type, water content, slope angle, and surcharge loading.
  • Granular soils have a natural angle of repose of around 30 to 35 degrees.
  • Cohesive soils may stand steeper initially but can fail suddenly without warning.
  • Water is the most common trigger for slope failure — rainfall weakens the soil.
  • Heavy plant near the crest adds surcharge loading that can trigger failure.
  • Stockpiles must be kept at least 1 metre back from excavation edges.
  • CDM 2015 requires slope stability to be assessed in the construction phase plan.
  • Monitoring for cracks, bulging, and water seepage should be carried out daily.
  • Temporary slopes must be assessed by a competent geotechnical engineer on high-risk sites.

Why?

Prevent burialSlope failures bury workers under tonnes of soil — extraction takes too long.
Unpredictable failureClay slopes can stand for days then fail suddenly without warning.
Weather sensitivityRainfall dramatically reduces stability, making daily assessment essential.
Legal dutyCDM requires slope stability risks to be assessed and managed.
Do Don't
  • Assess slope stability before allowing anyone to work at or below a slope.
  • Design temporary slopes based on geotechnical advice for the conditions.
  • Keep stockpiles at least 1 metre back from excavation and slope edges.
  • Monitor slopes daily for cracks, bulging, water seepage, or movement.
  • Reduce slope angles or install support if water content increases.
  • Keep heavy plant away from the crest of temporary slopes.
  • Install drainage to divert surface water away from slope faces.
  • Re-assess slopes after heavy rainfall, freeze-thaw, or vibration.
  • Brief operatives on signs of impending slope failure.
  • Stop work and evacuate if slope movement or cracking is observed.
  • DON'T work at the base of an unassessed or unsupported steep slope.
  • DON'T park heavy plant or stack materials at the top of a slope.
  • DON'T assume a slope is stable because it has been standing for days.
  • DON'T excavate into the toe of a slope without engineering assessment.
  • DON'T ignore cracks, tension lines, or water seepage on a slope face.
  • DON'T stockpile excavated material at the edge of an excavation.
  • DON'T continue earthworks during heavy rainfall without reassessing.
  • DON'T allow water to pond at the crest of a temporary slope.
  • DON'T remove vegetation from slopes without considering stability impact.
  • DON'T undercut slopes to create extra space without approval.

See also: Groundworks Safety Awareness | Excavation Safety Awareness
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