Field Permeability Testing (Lefranc/Lugeon) in Dublin

Dublin's foundation conditions tell a story shaped by ice. Beneath the city streets, a complex legacy of glacial till, fluvio-glacial gravels, and the dark Dublin Boulder Clay controls how water moves through the ground. Anyone excavating a basement in Ballsbridge or designing a SuDS drainage system in Clontarf faces a straightforward question: how permeable is the soil right here, right now? A desk study will not answer that. The local geology varies sharply over short distances, and assumptions about hydraulic conductivity can prove expensive. That is where the team runs in-situ Lefranc and Lugeon tests, capturing water flow data directly from the strata. Before committing to a dewatering strategy, it is often wise to combine permeability data with an SPT drilling campaign to log the sequence of stiff clays and lens-like sand pockets that define Dublin's drift geology.

A single in-situ Lefranc test in Dublin Boulder Clay is worth a dozen lab permeameter runs when designing a construction dewatering system.

Process overview

The Lefranc test setup in Dublin typically deploys a slotted standpipe installed within a borehole, sealed with a bentonite packer to isolate a specific horizon. Water is introduced or allowed to fall, and the rate of head dissipation is measured. In the dense, stony tills of south Dublin, the constant-head variant often proves more practical, as falling-head tests would take far too long in low-permeability clay matrices. For bedrock assessments in the granite outcrops near Dún Laoghaire or the Carboniferous limestones under the city centre, the Lugeon method applies packer-sealed pressurised water injection directly into the rock mass. A pressure gauge at the collar records the Lugeon value, which directly informs grouting decisions. Many projects benefit from linking the test results to a grain size analysis of the same horizon, because Dublin Boulder Clay often contains a bimodal mix of silt and cobbles that skews lab-derived permeability estimates compared to field-scale behaviour.

Local context

The risk profile changes dramatically between Dublin 4 and Dublin 22. In the low-lying, reclaimed docklands around Grand Canal Dock, high groundwater in alluvial gravels can flood an excavation within hours if permeability is underestimated. A contractor who assumes the dense clay found in Sandyford will encounter loose, water-bearing gravels in the quays area and face a completely different dewatering challenge. Conversely, in the hillside developments of Kilternan, fractured granite can produce preferential flow paths that a standard Lefranc test in overlying till would entirely miss. The Lugeon test becomes the only reliable way to quantify those discrete fracture flows. Combining permeability data with a slope stability analysis is particularly relevant where cut slopes in weathered rock are planned, because pore pressure distribution directly controls the factor of safety during and after rainfall events.

Reference standards

BS 5930:2015 + A1:2020 — Code of practice for ground investigations, Eurocode 7 (EN 1997-2:2007) — Ground investigation and testing, IS EN ISO 22282-2:2012 — Geotechnical investigation and testing — Geohydraulic testing — Water permeability tests in a borehole using open systems, Irish Building Regulations, Technical Guidance Document A (Structure)

Technical data

Parameter	Typical value
Test Standard	BS 5930:2015 + A1:2020 / Eurocode 7 (EN 1997-2)
Test Types	Lefranc (constant/falling head) in soil; Lugeon (packer test) in rock
Measured Parameter	Hydraulic conductivity k (m/s) / Lugeon value (LU)
Borehole Diameter	Typically NQ (75.7 mm) to HX (99.2 mm) depending on target depth
Packer Type	Single or double pneumatic packer for bedrock Lugeon testing
Reporting	Field data sheets, time-drawdown plots, k-value summary table
Accreditation	INAB ISO/IEC 17025 accredited laboratory oversight

Common questions

What does a field permeability test cost in Dublin?

A single Lefranc test in a soil borehole typically ranges from €600 to €850, while a Lugeon packer test in rock runs approximately €720 to €1010, depending on borehole depth, access constraints, and the number of test intervals. Mobilisation and traffic management in Dublin city centre zones can influence the final figure.

When do I need a Lugeon test instead of a Lefranc test?

The Lugeon test is designed for rock mass permeability assessment. If the site investigation encounters competent limestone or granite bedrock beneath the overburden, a Lugeon test with a packer system is the correct method. The Lefranc test is strictly for soils and will not yield meaningful data in fractured rock.

How long does an in-situ permeability test take on a Dublin site?

A single Lefranc test interval, once the borehole is advanced and the standpipe is placed, usually requires one to two hours to reach steady-state conditions in granular soils. In low-permeability Dublin Boulder Clay, a falling-head test may need three to four hours of monitoring. A multi-stage Lugeon test in bedrock can take a full day.