Hand dug trial pits, test pits and trial holes typically extend to 0.75m or 1.50m and are aimed to expose the existing foundations and provide samples for geotechnical and contamination testing. These are also useful to locate services such as electricity and gas in a safe and controlled manner. The location of any trial pit or borehole is first checked with a CAT scanner or cable detection tool to avoid interference with services.
Machine dug trial pits can extend to between 1.5m and 5m depth but typically 3m and provide good visual assessment of the ground. The pits can be dug using various standard diggers, depends of the dept requirement and access restrictions.
This is a cheap, quick and flexible method but larger excavations and machines can cause considerable disturbance and damage to the ground and involves higher risk for damage to utility services and underground installations. For this reason we usually recommend large trial pit excavation to be replaced by smaller test holes made by micro and mini digger and in particular Boreholes using window sampler and tracked mini rigs.