Trial pits: look and see.
- Dug by machine or by hand, usually to about 1 to 4.5m.
- Show the strata clearly, and give large bulk samples.
- Quick and good value.
- Need space for an excavator, and can disturb a garden more than a small borehole.
Trial pits or boreholes?
Both let you see what is under your site. A trial pit opens the ground up so you can look at it; a borehole goes deeper through a small hole. Which you need depends on how deep the questions go.
Boreholes: go deeper.
- Window sampling reaches around 6m quickly, even in tight gardens.
- Cable percussion boreholes can reach up to 60m, with high-quality samples and SPTs.
- Rotary drilling goes into bedrock and finds old mine workings.
How to choose.
For shallow foundations on straightforward ground, trial pits may be all you need. Where foundations or piles need information deeper down, where access is tight, or where there may be old workings, boreholes come in. Many sites use both: pits for the detail near the surface, boreholes for depth.
Quick answers.
What is the difference between trial pits and boreholes?
A trial pit is an open excavation, usually up to about 4.5m, that lets you see the strata and take large samples. A borehole is a small-diameter hole that can go much deeper.
Which is cheaper?
Trial pits are usually quicker and better value for shallow investigations. For deeper information, boreholes are the only option.
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