Trial Pitting

The Workhorse of the Site Investigation Industry

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Trial Pitting: The Workhorse of the Site Investigation Industry

Trial pitting is a general term used to describe a hole dug into the ground as part of a site investigation. Trial pits can be dug by hand, but are most often dug using a conventional mechanical excavator. Trial pits are perhaps the most cost-effective method of logging and sampling sub-surface soils for both environmental and geotechnical purposes.

At GCL, we often use a JCB 3CX excavator, or a Yanmar SV26 excavator. In cases where access is particularly tight, or only very shallow samples are required, our engineers will dig hand pits using specialist insulated hand-tools.

JCB 3CX Specifications

Minimum Width: 2350mm      

Minimum Height: 3000mm

Length: 5600mm

Weight: ~8000kg

Max Dig Depth: 4m

JCB 3CX Excavator Data SheetDownload

Yanmar SV26 Specifications

Minimum Width: 1550mm

Minimum Height: 2435mm

Weight: 2740kg

Max Dig Depth: 2.8m

Yanmar SV26 Excavator Data SheetDownload

Trial Pitting Methodology

The exact methodology varies from site to site based on the site investigation purpose and the ground conditions. However, in most cases a 2ft toothed bucket is used to excavate a 0.50m x 1.50m pit to the required depth. Topsoil is normally kept to one side of the pit, with deeper arisings stockpiled on the other side, in the approximate order they came out of the hole. Trial pits should always be backfilled in 300mm horizons in the order they were excavated, and compacted frequently using the excavator bucket. Trial pits are often left slightly mounded to allow for future settlement.

Trial Pit Uses

Trial pitting is an extremely versatile investigation technique and can be used in the following applications;