Mechanical digging to determine the characteristics of the site’s soil composition

The excavation of Trial Pits is a relatively quick method of investigation to determine the site’s soil characteristics and attributes by providing a good visual assessment of the soil profile and by obtaining large bulk soil samples for further laboratory testing.

The depth of investigation is limited to the reach of the equipment used. Hand dug Trial Pits are typically dug to a maximum of 1.2m. A standard tractor-mounted backhoe is typically able to dig to 2.5m, while a larger track-mounted excavator could reach up to 5m depth.

The full depth of excavation may be limited by:

• Refusal on competent material such as rock or concrete
• The presence of excessive groundwater
• The collapse of sidewalls in non-cohesive sands and gravels
• Risk to surrounding structures

Hand-dug Trial Pits are often used to carry out an assessment of existing foundations, shallow obstructions, or underground services where machine excavators may damage these. Machine excavated Trial Pits can also be used to undertake Soakage Testing.