In-Situ Permeability Testing (Lefranc & Lugeon) in Saint-Hyacinthe

In Saint-Hyacinthe, you quickly learn that managing groundwater is not just a specification box to tick; it is the defining challenge of any excavation below the Yamaska River plain. We commonly observe contractors surprised by artesian conditions in the till, a scenario easily missed without a properly executed field permeability test. This is why our technical team runs Lefranc tests in the granular overburden and Lugeon tests when we hit the fractured bedrock, providing the hydraulic conductivity data that determines pump sizing and cutoff wall depth. For deeper investigations, integrating these results with CPT testing helps us delineate drainage boundaries in the silty lenses typical of the Montérégie region.

A Lugeon value of less than 1 in the bedrock doesn't mean it's waterproof; it means the jointing system is tight and grout takes will be minimal.

Process and scope

With a population over 55,000, Saint-Hyacinthe sits at an elevation of roughly 30 meters above sea level, but the real story is underground: the Champlain Sea clay deposits transition into dense glacial till at variable depths. A standard Lefranc test here must distinguish between the weathered crust and the intact clay, which can have permeability values differing by two orders of magnitude. When the Saint-Germain fault zone influences the bedrock, a Lugeon test becomes essential to measure secondary fracture permeability. We perform these tests strictly under ASTM D6391 for rock mass characterization, and we often recommend supplementary grain size analysis to correlate field data with the fine-grained nature of the local marine soils.

Local geotechnical context

The most common mistake we see in Saint-Hyacinthe is using laboratory permeameter results on Shelby tube samples to design a full-scale dewatering system. The marine clays here are notoriously fissured; a small lab sample cannot represent the macro-porosity created by desiccation cracks or root holes in the crust. A Lefranc test measures this bulk mass permeability correctly. Skipping the field test leads to undersized pumps, prolonged construction delays during spring thaw, and catastrophic base heave in excavations near the Yamaska River. We also see engineers failing to distinguish between Lugeon pattern types—an 'erosion' pattern during the test signals that natural fines are being washed out, a critical warning for long-term stability that a simple water pressure test would miss.

Technical data

Parameter	Typical value
Test Method (Soil)	Lefranc (Constant/Falling Head)
Test Method (Rock)	Lugeon (Packers, 5-pressure stages)
Applicable Standard (Soil)	ASTM D6391 / CSA A23.3 context
Typical Test Depth	Up to 30 m below grade
Measured Parameter	Hydraulic Conductivity (k, cm/s)
Packer Type	Single or Double Pneumatic
Pressure Range	0-150 psi (regulated)

Complementary services

Lefranc Testing in Overburden

We install the test cavity at the exact depth of your proposed excavation base, using a falling or constant head procedure to derive the in-situ coefficient of permeability. This method excels in the stratified silts and clays of the Saint-Hyacinthe region where lab tests fail.

Lugeon Testing in Bedrock

We isolate specific fracture zones with inflatable packers and apply five steady pressure steps. Analyzing the flow versus pressure curve reveals not just the Lugeon value, but also the mechanical behavior of the fractures, critical for designing grout curtains in the local limestone and shale formations.

Common questions

How long does a typical Lefranc test take in the Saint-Hyacinthe clay?

Once the borehole is advanced to the test depth, the actual test phase usually takes between 60 and 90 minutes. However, in the low-permeability Champlain clays common here, the stabilization time for a falling head test can extend to several hours to ensure the readings are asymptotic and not transient.

What is the difference between a Lugeon value and hydraulic conductivity?

A Lugeon unit is defined as 1 liter of water per meter of test section per minute at 1 MPa pressure. While roughly equivalent to a hydraulic conductivity of 1x10^-7 m/s, the Lugeon test is specifically a rock mass test. It captures the combined effect of matrix porosity and fracture flow, which is the dominant transport mechanism in the bedrock beneath Saint-Hyacinthe.

What is the typical cost range for a field permeability test in Montérégie?

For a standard Lefranc or single Lugeon test setup, including drilling and technical reporting, the typical budget in Saint-Hyacinthe falls between CA$750 and CA$1,290. The final cost depends on the overburden depth, access constraints, and the number of test intervals required.

Do I need a Lugeon test if I am installing a shallow footing?

If the footing is in soil, a Lefranc test is appropriate. You only need a Lugeon test if the bedrock is within the influence zone of the structure or if you are analyzing uplift pressures. In Saint-Hyacinthe, where the rockhead can be shallow near the Saint-Thomas-de-Foucault area, we often specify a Lugeon test to check for artesian uplift risks under the footing.