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Home › In-Situ Testing › Field permeability test (Lefranc/Lugeon)

In-Situ Permeability Testing (Lefranc & Lugeon) for Portlaoise Ground Conditions

Practical geotechnics, field-tested.

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The bedrock beneath Portlaoise is predominantly Dinantian limestone, but what governs drainage on any given site is the overburden — a mixed mantle of glacial till and alluvial gravels deposited by the River Triogue. Permeability can vary by orders of magnitude within a single hectare. A borehole log tells you what the soil is; a field permeability test tells you how water actually moves through it. In our experience across the Midlands, assuming a textbook value for 'sandy gravel till' leads to oversized dewatering systems or, worse, flooded excavations. The Lefranc test gives us point measurements of hydraulic conductivity in soil, while the Lugeon test is the standard for assessing fracture flow in the underlying limestone — essential when a basement excavation in Portlaoise encounters weathered bedrock at 3 to 5 metres depth. We run these tests under constant or falling-head conditions, following IS EN ISO 22282 series, and report k-values directly usable for drain design or groundwater control planning.

A single field permeability test in Portlaoise till is worth more than ten desk-study estimates when groundwater is within excavation reach.

Our service areas

In-Situ Testing

Field density test (sand cone method) ›Plate load test (PLT) ›Field permeability test (Lefranc/Lugeon) ›
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Laboratory

Grain size analysis (sieve + hydrometer) ›Triaxial test ›Atterberg limits ›
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Geophysics

MASW / VS30 (shear wave velocity) ›Electrical resistivity / VES (Vertical Electrical Sounding) ›Seismic tomography (refraction/reflection) ›
VIEW ALL GEOPHYSICS ›

How we work

A recent project on the Abbeyleix Road involved a commercial building with a deep basement cutting into silty gravel overlying karstified limestone. The contractor needed a reliable estimate of inflow before committing to a wellpoint system. We installed boreholes at three locations, sealing each test section with a pneumatic packer to isolate the target horizon. In the upper gravel, five Lefranc tests — three rising-head, two constant-head — returned k-values ranging from 1.2 × 10⁻⁴ to 8.7 × 10⁻⁵ m/s, confirming high permeability and the need for active dewatering. The Lugeon test in the underlying limestone, conducted over a 3-metre interval, showed a Lugeon value of 18, indicating moderately open fractures that would contribute additional inflow once the excavation reached rockhead. The water table in central Portlaoise is often shallow, typically 1.5 to 2.5 metres below ground level during winter, so the test depth and packer placement must account for seasonal fluctuation. We log groundwater level before, during, and after each test to verify that steady-state conditions are achieved. All testing is supervised by a geotechnical engineer who documents the pressure-flow response curve on site — a Lugeon pattern of turbulent flow versus laminar fracture flow changes the interpretation significantly.
In-Situ Permeability Testing (Lefranc & Lugeon) for Portlaoise Ground Conditions
Technical reference — Portlaoise

Local ground factors

Portlaoise has grown rapidly from a market town into a commuter hub, pushing development onto marginal land between the Triogue floodplain and the M7 corridor. The glacial stratigraphy here is erratic: lenses of dense boulder clay sit next to open-work gravel channels that can transmit water from kilometres away. Underestimating permeability in these gravels means a dewatering system sized for 2 litres per second suddenly faces 15. Add the limestone karst — solution features and buried hollows are common across the Laois plain — and you have a scenario where a basement excavation can flood from a fissure that had no surface expression at all. A Lugeon test performed too quickly, without stabilised pressure steps, will under-read fracture flow. A Lefranc test in silt without adequate filter sand can clog and give a false low. These are not hypotheticals; we have seen each of them in the Portlaoise area. The cost of a correct field permeability test is negligible against the cost of a failed dewatering scheme or a percolation system that the local authority rejects.

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Regulatory framework

IS EN ISO 22282-2:2012 — Geotechnical investigation and testing — Geohydraulic testing — Part 2: Water permeability tests in a borehole using open systems (Lefranc), IS EN ISO 22282-3:2012 — Geotechnical investigation and testing — Geohydraulic testing — Part 3: Water pressure tests in rock (Lugeon), IS EN 1997-2:2007 + NA:2010 — Eurocode 7: Geotechnical design — Part 2: Ground investigation and testing (Irish National Annex), TII Publication CC-SPW-01200 — Specification for Ground Investigation (guidance on in-situ permeability for road and bridge works in Ireland), Building Regulations 2010, Technical Guidance Document H — Drainage and Wastewater Disposal (percolation test context for single houses)

Technical data

ParameterTypical value
Test method (soil)Lefranc — constant head / falling head / rising head
Test method (rock)Lugeon — 5-pressure stage, 3 m test interval typical
Applicable standardIS EN ISO 22282-2 (soil), IS EN ISO 22282-3 (rock)
k-value range measurable10⁻³ to 10⁻⁷ m/s in soil; 0–100+ Lugeon units in rock
Borehole diameter76 mm to 150 mm, depending on packer configuration
Typical test depth, Portlaoise2.5–8.0 m for soil; 5.0–15.0 m for bedrock
Reporting outputHydraulic conductivity k (m/s), Lugeon value, flow regime interpretation

Common questions

What does a field permeability test cost in the Portlaoise area?

A single Lefranc test in soil typically ranges from €510 to €680, while a Lugeon test in rock ranges from €630 to €810, depending on borehole depth, number of test intervals, and packer configuration. A combined soil-rock testing programme across two or three boreholes is the most common request we see for Portlaoise basement projects. All prices include engineer attendance, data interpretation, and a signed test report.

When is a Lugeon test required instead of a Lefranc test?

Lefranc tests are designed for soil and granular materials; Lugeon tests are for rock. In Portlaoise, where limestone bedrock often lies within 3 to 5 metres of the surface, any excavation that reaches or penetrates rock should include Lugeon testing. The test measures water take in litres per minute per metre of test interval at a standard pressure of 1 MPa, producing a Lugeon value that indicates fracture openness. A value above 5 generally means grouting or dewatering will be needed.

How long does a field permeability test take on site?

A single Lefranc test on a pre-drilled borehole takes 45 to 90 minutes, depending on soil type and whether we use constant or falling-head configuration. A Lugeon test with five pressure stages over a 3-metre interval takes approximately 90 to 120 minutes. For a typical Portlaoise investigation with two boreholes and tests in both soil and rock, plan for one full day on site plus mobilisation.

Can field permeability test results be used for percolation area design?

Yes, but with a distinction. For single-house wastewater treatment systems in County Laois, the standard percolation test (T-test) described in the EPA Code of Practice is the regulatory requirement. However, for larger developments or where ground conditions are marginal, a Lefranc test provides a more rigorous hydraulic conductivity value that can support an application to the local authority. We recommend discussing the testing approach with your consulting engineer before proceeding.

What preparation is needed before the test team arrives?

The borehole must be drilled, cased, and cleaned to the target test depth before permeability testing begins. We coordinate directly with the drilling contractor to ensure the borehole diameter matches the packer size and that the test interval is free of drilling mud or cuttings. The client or main contractor is responsible for site access, any traffic management on public roads, and for locating underground services prior to drilling. We supply the packer assembly, flow meter, pressure transducer, and all measurement equipment.

Location and service area

We serve projects in Portlaoise and surrounding areas.

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