Ground investigation works including trial pits, boreholes, and window samples provide essential information about soil conditions, contamination, and underground services. Trial pits are open excavations that expose workers to collapse, contaminated ground, and underground service strikes. This talk covers the hazards specific to ground investigation activities and the controls every operative must follow during these works.
Key Hazards
Trial pit collapse burying workers in unsupported shallow excavations
Striking underground services during machine-dug investigation pits
Contact with contaminated soil, groundwater, or hazardous fill materials
Workers entering unsupported trial pits to take samples or inspect strata
Control Measures
Carry out a CAT and Genny survey and obtain utility records before excavating any trial pit.
Support or batter trial pit sides if any person needs to enter the excavation for sampling.
Fence and sign all open trial pits to prevent unauthorised access and falls into the excavation.
Wear PPE appropriate to the expected ground conditions including gloves, overalls, and RPE if needed.
Review the desk study and contamination risk assessment before starting any investigation work.
Take soil and water samples from outside the pit using long-reach tools wherever possible.
Backfill completed trial pits promptly and reinstate the surface to prevent ongoing access hazards.
Brief the investigation team on expected ground conditions, contamination risks, and service locations.
Record all trial pit locations, depths, and findings on the site investigation plan for future reference.
Remember
Complete a CAT and Genny survey and obtain utility records before excavating any trial pit
Support or batter pit sides before any person enters the excavation for sampling or inspection
Fence and sign all open trial pits to prevent unauthorised access and falls
Review the desk study and contamination risk assessment before starting investigation works
Take samples from outside the pit using long-reach tools wherever it is practicable to do so
Backfill completed trial pits promptly and reinstate the surface to remove ongoing hazards
Applicable Legislation: CDM Regulations 2015 · BS 5930:2015 (Ground Investigation) · HSG47 (Avoiding Danger from Underground Services) · Health and Safety at Work etc. Act 1974