Trial pits (sometimes known as foundation pits, trial holes & trial trenches) are Constructive Evaluation’s most common geotechnical works. But what exactly are they and why do we use them?
What are Trial Pits?
Put simply, Trial pits are exploratory holes dug to help assess ground conditions and foundations prior to construction works. These pits come in two forms, hand dug and machine excavated.
Hand Dug Trial pits
Hand-excavated trial pits are typically placed external to the building, to determine the vertical and lateral extent of any existing foundations. They are particularly desirable for small-scale site investigations or where the trial pits need to avoid underground obstacles such as cabling and service pipes. A hand-dug pit would typically be anywhere from 1m to 2m meters deep. These test pits are useful for gathering shallow samples for geo-environmental screening or to determine the location of underground utilities and structures. Additionally, hand-dug trial pits can be used to expose existing foundations for additional analysis, WAC testing, and contaminant testing.
Machine Excavated Trial Pits
The benefit of mechanically excavated pits over hand dug are that greater depths are achievable (up to 4m) and pits and trenches can cover a large area, quickly. This is the most favourable investigation method for multi-plot housing developments. This can however have downsides. Whilst every care is taken to avoid issues, excavators are much more indiscriminate than manual digging and so they’re not recommended in areas with a lot of utilities.
Benefits
When it comes to geotechnical and geo-environmental testing, there are numerous options for exploratory holes. What are the benefits of Trial pits over percussive drilling, boreholes or window/windowless samples?
One benefit is that trial pits are quicker to carry out than the other methods mentioned. They can also give an idea of ground conditions not only at depth, but across an area. They also have the added versatility of being used for various other tests such as soakaways, Dynamic probes, standard penetration tests, shear vanes, percolation testing and much more.
Perhaps the biggest advantage over other methods; and most importantly for our clients, is that trial pitting is much more cost effective than boreholes and window/windowless sampling.
Find Out More
For more information on Trial Pitting, click here. Click here to find out more about our other in-situ testing services. To learn more about the other geotechnical services we offer, click here. If you need some trial pitting, or you wish to discuss your requirements with a qualified geotechnical engineer, contact us.
