EXC/General/TBT-EXC-013

Ground Conditions Assessment

Excavations › General › Ground Conditions Assessment

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Ground conditions assessment evaluates soil type, water table, stability, and hazards before excavation begins.
Different soils behave differently: clay stands better than sand, but both collapse without warning when saturated.
The water table level determines whether dewatering is needed and affects excavation side stability.
Previous site use may have left contamination, buried structures, voids, and unrecorded services underground.
Ground investigation reports from boreholes and trial pits provide factual data about subsurface conditions.
Visual assessment during excavation should confirm whether conditions match the ground investigation findings.
Unexpected conditions including running sand, perched water, and soft pockets require immediate reassessment.
The excavation support system must be designed for the actual ground conditions found, not assumed conditions.
CDM 2015 requires that ground conditions information is provided as part of pre-construction information.
A competent person must assess ground conditions before each excavation and after any significant change.

Collapse prevention	Excavation support designed for the wrong soil type fails, causing collapse that buries and kills workers.
Unexpected hazards	Unknown contamination, voids, and water pockets create sudden dangerous conditions if not identified in advance.
Legal duty	CDM 2015 requires ground condition information to be provided and used for safe excavation planning.

Don't

Review the ground investigation report before planning any excavation work.
Assess the soil type visually as excavation proceeds and compare with reports.
Check the water table level and plan dewatering before reaching it.
Design excavation support for the actual ground conditions confirmed on site.
Stop work and reassess if ground conditions differ from those expected.
Look for signs of contamination including unusual colours, smells, and debris.
Inspect excavation sides after rain, frost, or changes in weather conditions.
Brief the excavation team on the expected ground conditions and hazards.
Record actual ground conditions encountered for comparison with the investigation.
Consult a geotechnical engineer if unexpected conditions are found during excavation.

DON'T excavate without reviewing the available ground investigation data first.
DON'T assume ground conditions are the same across the entire site.
DON'T use standard excavation support without confirming it suits the actual ground.
DON'T ignore running water, soft ground, or unexpected voids during excavation.
DON'T continue excavation if conditions differ significantly from the investigation report.
DON'T rely on the surface appearance to judge what lies below ground.
DON'T skip reassessment of excavation sides after heavy rain or overnight frost.
DON'T enter excavations in granular soils without adequate support regardless of depth.
DON'T dismiss unusual smells or discolouration as harmless without investigation.
DON'T assume the absence of a ground investigation means conditions are straightforward.

See also: Excavation Safety Awareness | Trench Collapse Prevention

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