Dundalk’s growth from an early medieval settlement on the Castletown River to a major manufacturing and logistics hub has placed increasing demands on its underlying geology. The town sits on a complex sequence of glacial tills, alluvial gravels, and the underlying mudstones of the Carlingford Limestone Group, creating a highly variable hydrogeological regime. For any deep excavation, basement construction, or landfill assessment, understanding the mass permeability of these deposits is not optional—it is a fundamental design input. Our field permeability testing programme applies the Lefranc method in soils and the Lugeon test in rock to measure hydraulic conductivity directly, feeding reliable k-values into seepage analyses for deep excavations and dewatering system design. With a laboratory accredited to ISO 17025 and field procedures aligned with BS EN ISO 22282-2:2012, the test data withstands the scrutiny of local authority planning departments and the rigorous review of consulting engineers working across the Dublin–Belfast corridor.
A single Lefranc test in a gravel lens can reveal a permeability contrast of five orders of magnitude—data that no laboratory triaxial test on a 100 mm sample can reproduce.
Service characteristics in Dundalk
Critical ground factors in Dundalk
In Dundalk, many sites on the northern side of town encounter a thin blanket of glaciofluvial outwash overlying lodgement till. What catches out inexperienced ground investigators is the perched water table trapped within that outwash layer, often just two to three metres below ground level. Borehole water strikes recorded during dry drilling can be misinterpreted as the regional groundwater level if observation wells are not installed with proper bentonite seals. A Lefranc test performed without isolating the test zone from the overlying gravel will produce an integrated k-value that overestimates the bulk permeability of the till by a factor of a thousand or more. The consequence: a dewatering system designed for the wrong aquifer, leading to either excessive pumping costs or, worse, basal instability in the excavation. Where Lugeon testing is specified in the underlying mudstone, we insist on packer seating in competent rock at least one metre above and below the test interval, because leakage past the packer through stress-relief fractures in the borehole wall can yield falsely high Lugeon values. These are not academic concerns—they are the difference between a dry excavation and a flooded one.
Our services
Our Dundalk-based field permeability testing programme covers the full spectrum of in-situ hydraulic conductivity measurement. Each test is configured to the specific stratum and project requirement, with results interpreted against established analytical models and the local geological framework of the Irish Quaternary.
Lefranc Permeability Testing in Soils
Variable-head and constant-head Lefranc tests executed through cased boreholes in glacial tills, sands, and gravels. We isolate the test cavity with a sand pack and bentonite seal to prevent vertical leakage, measuring drawdown response with a pressure transducer and datalogger. Results are analysed using the Hvorslev shape-factor method appropriate to the cavity geometry, yielding a stratum-specific k-value directly applicable to groundwater inflow calculations and dewatering design.
Lugeon Testing in Rock Mass
Down-the-hole Lugeon testing with single or double pneumatic packers in fractured mudstone, limestone, and greywacke. Each 3 to 5-metre test stage is pressurised at five increments following the Houlsby procedure, allowing us to characterise the flow regime as laminar, turbulent, dilation, washout, or impermeable. This classification guides grouting decisions for dam foundations, tunnelling pre-injection, and cut-off wall design.
Frequently asked questions
When is a Lefranc test more appropriate than a laboratory permeability test on a soil sample?
The Lefranc test measures the bulk hydraulic conductivity of a soil mass in situ, capturing the influence of fissures, sand lenses, gravel partings, and macro-structure that a small 100 mm laboratory specimen cannot represent. In glacial tills typical of County Louth, laboratory tests on intact samples often underestimate mass permeability by two to three orders of magnitude. Whenever groundwater control is critical—such as for deep basements, pipeline trenches, or slope drainage—the in-situ measurement provides the design parameter that truly governs seepage rates.
What does a Lugeon value actually tell the design engineer?
One Lugeon unit equals a water absorption of one litre per minute per metre of test interval at an effective pressure of 1 MPa. Values below 3 typically indicate tight rock requiring minimal treatment; 3 to 10 suggests joint-controlled flow amenable to targeted grouting; above 20 often signals open fractures or karstic features needing systematic injection. Beyond the numerical value, the Houlsby interpretation of the pressure-flow curve reveals whether the rock mass dilates under pressure (reversible) or washes out infill material (permanent increase in permeability)—a distinction crucial to dam grouting specifications.
What is the typical cost range for a Lefranc or Lugeon testing programme in the Dundalk area?
A field permeability assessment including two to three Lefranc tests within an existing borehole programme generally falls between €640 and €980, depending on the number of test intervals, depth, and whether falling-head or constant-head configurations are used. Lugeon testing in rock typically costs more due to packer equipment and the multi-stage pressure protocol. We provide a fixed-price proposal after reviewing the borehole logs and project groundwater requirements.