Field Permeability Testing (Lefranc/Lugeon) in Prince George

Prince George grew up around the confluence of the Nechako and Fraser Rivers, and that riverine geography still dictates every foundation decision today. Much of the city sits on thick glaciofluvial deposits where clean gravels alternate with silty lenses, creating tricky permeability contrasts. At our geotechnical laboratory, we run field permeability tests (Lefranc and Lugeon) to quantify hydraulic conductivity directly in the borehole. These tests feed into dewatering plans for deep excavations along the Highway 16 corridor and seepage assessments for tailings facilities north of town. When grain-size curves alone cannot capture the in-situ fabric, a triaxial test on undisturbed Shelby tube samples helps correlate lab and field hydraulic behavior under confining pressure.

In glacial stratigraphy, a single Lugeon stage run at the wrong pressure can mask a conductive fracture set — five-stage testing is non-negotiable.

Methodology applied in Prince George

One thing we consistently see in Prince George: the variable thickness of the glaciolacustrine silt unit overlying the till. That silt layer can be 2 m thick at one borehole and nearly absent at the next, flipping the drainage regime from slow seepage to rapid gravel flow within a single building footprint. Our Lefranc testing isolates discrete intervals in soil, typically using a falling-head or constant-head method; Lugeon testing in bedrock evaluates fracture connectivity via five pressure stages per ASTM D4630. The resulting k-values, usually ranging from 1×10⁻⁷ to 1×10⁻³ m/s, dictate wellpoint spacing and sump sizing. For road embankments crossing muskeg terrain west of the city, we pair permeability data with CBR testing for road design to ensure subgrade stability under saturated conditions. On sites where silt pockets suggest potential liquefaction under seismic loading, the borehole log gets cross-checked with a liquefaction assessment using SPT blow counts and fines content.

Field Permeability Testing (Lefranc/Lugeon) in Prince George

Parameter	Typical value
Test standard (soil)	ASTM D4631 (Lefranc – falling/constant head)
Test standard (rock)	ASTM D4630 (Lugeon – five pressure stages)
Typical k range measured	1×10⁻⁸ to 5×10⁻³ m/s
Borehole diameter	NW/NWL (76 mm) or HQ (96 mm), depending on overburden
Lugeon pressure steps	P_min, P_int, P_max, P_int, P_min (ascending/descending)
Test interval length	0.5–2.0 m in soil, 3.0–6.5 m in rock (packer spacing)
Reporting parameter	Lugeon value (Lu) or k (m/s), flow vs. pressure curve

Typical technical challenges in Prince George

The Nechako River underfit valley contains buried paleochannels filled with loose, highly permeable gravels that do not appear on surface geological maps. Hitting one of these channels unexpectedly during a test pit excavation can flood the pit within minutes, even in February when the ground is frozen. A Lefranc test performed at 3–5 m depth in these gravels often returns k-values exceeding 1×10⁻³ m/s, demanding a complete rethink of the temporary works. Overestimating the silt continuity and under-designing the dewatering system leads to base instability in footing excavations and repeated construction delays. ASTM D4631 and D4630 provide the procedural backbone, but interpreting the flow regime — laminar versus turbulent — requires local experience with Prince George hydrogeology.

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Applicable standards: ASTM D4631 – Standard Test Method for Determining Transmissivity and Storativity of Low Permeability Rocks by In Situ Measurements Using the Pressure Pulse Technique (referenced for Lefranc methodology in soil), ASTM D4630 – Standard Test Method for Determining Transmissivity and Storage Coefficient of Low-Permeability Rocks by In Situ Measurements Using the Constant Head Injection Test (Lugeon), NBCC 2020 – Geotechnical site investigations for seismic and groundwater considerations, CSA A23.3 – Concrete structures in contact with groundwater (durability exposure classes)

Our services

Our field permeability testing program in Prince George covers the full workflow from borehole selection to hydraulic parameter reporting.

Lefranc testing in overburden

Falling-head and constant-head permeability tests in soil, isolating screened intervals within glacial till, glaciofluvial sands, and lacustrine silts.

Lugeon testing in bedrock

Five-stage packer testing in fractured shale and sandstone bedrock to determine Lugeon values and assess groutability for cut-off curtains.

Packer permeability profiling

Multi-interval straddle-packer setups for vertical hydraulic conductivity profiling in exploration boreholes deeper than 30 m.

Dewatering parameter reporting

Reduction of field k-values to design inputs for wellpoint dewatering systems, open-cut sump sizing, and groundwater control permits.

Frequently asked questions

What is the difference between a Lefranc test and a Lugeon test?

A Lefranc test measures hydraulic conductivity in soil by injecting or withdrawing water through a screened interval, typically using falling-head or constant-head methods per ASTM D4631. A Lugeon test measures hydraulic conductivity and fracture behavior in rock by injecting water under five pressure stages per ASTM D4630, yielding a Lugeon value (1 Lu ≈ 1×10⁻⁷ m/s). In Prince George, we use Lefranc for the surficial glaciofluvial deposits and Lugeon for the underlying fractured bedrock.

How long does an in-situ permeability test take in the field?

A single Lefranc test in soil usually takes 30 to 60 minutes, depending on soil type and whether we run both falling-head and constant-head stages. A five-stage Lugeon test in rock typically requires 45 to 90 minutes per test interval. We can run multiple tests per day, provided the borehole stays open and stable.

What does a field permeability test cost in the Prince George area?

Field permeability testing in Prince George ranges from CA$810 to CA$1,260 per test interval, depending on depth, access conditions, and whether it is a Lefranc or Lugeon procedure. Mobilization, drilling crew time, and packer equipment are included in this range.

When is a Lugeon test required instead of a simple packer permeability test?

A Lugeon test is required when you need to assess fracture connectivity and groutability of bedrock — for dam foundations, cut-off curtains, or tunnel pre-excavation grouting. The five-stage pressure cycle reveals whether fractures dilate, wash out, or fill with fines under injection pressure, which a single-pressure test would miss.