Trial Pits & Holes Ireland
What Is a Trial Pit?
A trial pit is a hole dug into the ground to examine the subsurface’s structure and composition. Also called test pits, trial pitting and trial trenches – they help to examine soil, rocks and groundwater. Trial hole investigations take place before beginning construction projects so the conditions and composition of the soil and ground can be properly assessed.
They can often provide the most practical and economical method of site investigation and assessment. ESP often utilises trial pits to obtain samples and engineering logs of shallow strata and we consider the large in-situ exposure of soils to be of importance when dealing with variable ground conditions.
Trial pits are usually completed before construction works to assess the geology and water table of the site. Pits are excavated in intervals, typically 1 to 4 meters deep, by hand or machine. In a situation where there is any risk of coming into contact with utilities like water pipes or electric cables then digging by hand is the preferred approach.
If the hole required is deeper than 1.2 metres then reinforcement precautions are used to solidify the pit to ensure safety.
1. Hand Dug Trial Pit
Hand-dug trial pits are ideal for small-scale site investigations, especially where subsurface risks like pipes and cables are present. Typically, manual excavation pits are excavated to a depth of 1.2m to 1.5m. Before excavation, the surface can be scanned using a standard or advanced CAT scanner to detect underground obstructions such as utilities and structures.
Applications:
- Soil Sampling: Hand-excavated trial pits are often used to collect near-surface soil samples.
- Utility Location: They help in locating underground utilities and structures.
- Foundation Exposure: This method is also used to expose shallow, existing foundations for further assessment.
2. Machine Dug Trial Pits
Machine-dug trial pits are suitable for larger sites where extensive excavation is required. These pits typically range from 1.5m to 6m in depth, with a standard depth of around 3m being sufficient for most assessments.
Key Considerations:
- Ground Disturbance: The use of large machinery can cause significant ground disturbance, which must be managed carefully along with trial pit safety.
- Supplementary Testing: For deeper investigations, smaller test holes or boreholes may be recommended. These can be used for window sampling and mini rigs, offering a less disruptive alternative.
Why Use Trial Pits?
Here are some of the benefits of trial pits:
- The SI enables information to be collected to further characterise the Conceptual Model (S-P-R)
- The presumed Conceptual Ground Model can be updated with actual site data in real time
- The siting can be justified and compared with assumptions reasonably developed during desk-study
- It is not limited to the collection and analysis of samples to simply ascertain contaminant concentrations – the input to engineering geology and geotechnical assessments is valuable
- The sampling strategy can be modified whilst the investigation is in progress for little cost
It is also important to consider the Health and Safety implications of trial pitting, both during and after the investigation.
If you require any more information, please contact us today. A selected list of example projects can be found on our Projects and Technical page.
When Are Trial Pits Required?
Trial pits conducted as part of site investigations are often needed for the below situations:
- Site pre-purchase due diligence studies
- Contaminated land assessments
- Foundation design
- Subsidence surveys
- Part IIa investigations
- Environmental monitoring
- Insurance claims
- Mining surveys
- Relict foundation and obstruction assessment
- Ground improvement design
What is a Trial Hole Used For?
Often more cost-efficient than using a borehole, trial pits are used before work on a development site begins. They are conducted on stable ground, to assess the ground conditions as part of a site investigation. Trial pits are used to investigate large sample areas to examine the strata and conclude if any additional investigations are needed on the construction site.
Trial pitting is a helpful tool to examine:
- Sub-surface structures
- Variable ground conditions
- Soil conditions and profile
We can employ the use of a trial pit to take distributed and undistributed samples along with the use of other sampling methods such as:
- Vane Shear tests
- Soakaway tests
- CBR testing (per BRE 365 guidance)
- In-situ strength testing
Trial Holes & Works Completed By ESP
For previous trial pit works we have conducted please see some example projects below:
Project Example: Portlaoise, Republic of Ireland
The site involved the demolition and replacement of an existing place of worship.
A desk-based review indicated no obvious former contaminative uses, however, it had been previously developed for residential purposes.
The site was indicated to be underlain by glacial soils followed by the Carboniferous Limestone bedrock of the Allenwood Formation.
The main potential hazards included:
- Potential asbestos and other contamination from demolition of historic buildings and Made Ground.
- Volume change of fine-grained glacial soils and weathered bedrock.
- Ground dissolution within the limestone bedrock.
Investigation points were spread across the site to obtain a general overview of the ground conditions present. Locations were positioned to maximise the information that could be obtained:
- Windowless sampling was undertaken at the proposed structure location to inform the foundation design.
- Shallow hand-excavated trial pits were undertaken in the remainder of the site to assess the contamination status of the shallow soils.
- Dynamic cone penetrometer testing was undertaken in areas of proposed car parking.
Whilst generally low levels of contamination were noted, localised asbestos contamination was identified at low levels and advice for further assessment/remedial action was provided. Low risks were proven to be posed to environmental receptors (e.g. Carboniferous Limestone aquifer).
Our team of experts are available to discuss your site requirements call us on 02920 813385 and we’ll be happy to answer your questions.
A selected list of example projects can be found on our Projects and Technical page. If you have any questions or enquiries please contact us.
Our Trial Pit Services in Ireland
Earth Science Partnership proudly offers our full range of trial pit services across Ireland and Northern Ireland. We have considerable experience working in the area and have completed works previously, or can offer our services in the following notable locations, among many more:
- Dublin
- Belfast
- Cork
- Limerick
- Galway
- Derry
- Newtonabbey
- Bangor
- Waterford
- Lisburn
- Drogheda
- Dundalk
- Swords
Author: Matthew Eynon, Director
I am a UK Registered Ground Engineering Specialist and Chartered Engineering & Environmental Geologist with significant experience in Site Hazard Assessment, Remediation, Design, and Implementation across the Geoenvironmental and Geotechnical sectors in the UK and abroad.
I often work in multi-disciplinary teams advising other engineering and design professionals on the implications of ground hazards.
My work involves undertaking design, planning, management, and reporting of ground investigations, including investigations for new developments, and many bespoke studies including the assessment of hydrogeological settings, materials for earthworks, the impact of abandoned mine workings, remediation and stability assessment of soil and rock slopes/landslides, most notably the Pantteg Landslide in the Swansea Valley for which I have guided and presented assessments to Local Authority officers and the general public.
Page Last Updated: 17th August 2024