The Lefranc and Lugeon packer systems are lowered into a completed borehole, sealing off a test section with pneumatic inflatable bladders. In Montreal, where the limestone and shale of the Trenton Group are often fractured by glacial scouring, the Lugeon assembly delivers pressurized water in five-step sequences while a digital flowmeter captures the exact volume escaping into discontinuities. The Lefranc variant, operated in granular overburden across the St. Lawrence Lowlands, uses a constant or falling head within a screened casing segment, recording the rate of dissipation through sandy till or Champlain Sea silts. Both methods feed data directly into the in-situ permeability calculations required for dewatering design and basement drainage assessments.
A five-step Lugeon sequence in fractured Trenton limestone reveals not just permeability, but the critical pressure at which fracture dilation begins.
Service characteristics in Montreal
Critical ground factors in Montreal
In the densely built Griffintown corridor of Montreal, an undetected permeable joint set can inundate a foundation pit in just a few hours, and the expenses for emergency pumping plus settlement damage to adjacent structures far outweigh the cost of a well-executed packer test program. For a 25-storey mixed-use tower near the Peel Basin, excavation required a 14 m deep cut into limestone where the water table was only 3 m below street level. The contractor used a single packer set at 18 m depth with a maximum applied pressure of 5 bar; the flow rate surged suddenly at the third step, indicating fracture interconnection with the Lachine Canal. Without that real-time pressure-flow (P-Q) curve, the dewatering system would have been undersized by at least 40%, risking basal heave in the open excavation.
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Two configurations, each with dedicated instrumentation and analytical procedures, are deployed by the field team to address Montreal's subsurface conditions.
Lugeon Packer Testing in Rock
This technique is designed for the Trenton Group limestone and Utica shale. It utilizes a double-packer assembly that isolates 1 to 5 m intervals. Five pressure steps are each maintained for ten minutes, with flow and pressure recorded simultaneously in digital format. The derived Lugeon value and P-Q curve characterize fracture flow regimes, dilation thresholds, and the effective hydraulic aperture. Reports contain step-test graphs, transmissivity per interval, and recommendations for grouting cutoff depths.
Lefranc Variable-Head Testing in Overburden
This approach is applied in granular till, Champlain Sea clays, and sandy lenses above bedrock. A screened casing section is isolated and filled with water; the rate of head decline is monitored by a submersible pressure transducer at one-second intervals. The analysis applies Hvorslev's equations for point-source geometry, adjusted for wellbore storage. Data sheets output hydraulic conductivity (k) values for each test horizon, which are critical for sheet pile design and temporary excavation dewatering plans.
Top questions
What is the difference between a Lefranc and a Lugeon permeability test?
The Lefranc test measures hydraulic conductivity in soil or very soft rock by using a constant or falling head within a short screened section, analyzed via Hvorslev's method for a point piezometer geometry. The Lugeon test, in contrast, is specifically for fractured rock; it applies water under pressure through a packer-sealed interval in five incremental steps to examine the pressure-flow relationship, including fracture dilation and infill washout effects.
How long does a typical packer test take on a Montreal drill site?
For a single-interval Lugeon test with five pressure stages, active testing after borehole preparation typically requires 90 to 120 minutes, with additional time for water level recovery monitoring. In a Lefranc falling-head test in silty till, the dissipation curve may stabilize within 30 to 60 minutes, depending on the formation's hydraulic conductivity.
What is the approximate cost of a field permeability test in Montreal?
In the Montreal region, a typical packer permeability program budget—encompassing mobilization, single or double packer setup, data acquisition, and engineering interpretation—ranges from CA$770 to CA$1,280 per test interval, with variations due to depth, access conditions, and the number of zones tested.