A deep excavation near Steeles Avenue required a dewatering plan before shoring. The contractor assumed low permeability, but three weeks of pumping told a different story. Brampton’s subsurface is dominated by the Halton Till, a dense silty clay matrix with erratic sand and gravel lenses. Assuming hydraulic conductivity without in-situ measurement is a gamble that costs time and budget. The Lefranc test resolves this for soil; the Lugeon test quantifies rock mass permeability where the till transitions into shale bedrock. We execute both under ASTM D6391 protocols, delivering K values in m/s with documented water take per packer stage. For sites near the Etobicoke Creek floodplain, the measured K frequently exceeds desk-study estimates by an order of magnitude. The team applies variable-head and constant-head procedures depending on the piezometric surface, ensuring every number holds up under review by the TRCA or municipal engineers. A reliable permeability profile feeds directly into the excavation support design, which is why we often run these tests alongside an early test pit program to visually log the stratigraphy at the same locations.
The Halton Till varies from 10⁻⁹ m/s to 10⁻⁵ m/s within a single Brampton site; a desk K estimate simply cannot replace a staged Lefranc or Lugeon profile.
How we work
Brampton’s geology splits into two permeability regimes. North of Bovaird Drive, the till is overconsolidated, producing K values in the 10⁻⁹ to 10⁻⁸ m/s range, typical of a silty clay aquitard. South toward Highway 407, outwash sands interbedded with till create preferential flow paths where K jumps to 10⁻⁵ m/s. That contrast demands careful test interval selection. We isolate the zone of interest with pneumatic packers, run five or more pressure steps for a Lugeon profile, and plot flow against effective pressure to identify laminar versus turbulent conditions. A straight-line Lefranc test in a borehole takes under an hour per interval and follows the Hvorslev shape factor for the intake geometry. Results are corrected for temperature and viscosity per ASTM D5084 when the project spec requires it. The data feeds numerical groundwater models in MODFLOW or SEEP/W, giving the dewatering contractor real transmissivity values instead of textbook estimates. Where weathered shale appears at depths of 8 to 12 meters, the Lugeon value—often below 3 Lugeon units—confirms that grouting can seal the contact zone efficiently. We document every step with a field log signed by the site engineer and time-stamped photos of the setup, so the report withstands a third-party audit.
Local considerations
The Credit River and Etobicoke Creek corridors create a perched groundwater regime across much of Brampton. In spring melt or after a heavy summer storm, the water table can rise two meters in 48 hours. An excavation designed with a single K value from a textbook ignores this seasonal swing. We have walked onto sites where the initial dewatering system was overwhelmed because the design assumed a homogeneous till, missing a gravel stringer that delivered 10 L/s into the cut. The Lefranc test catches these heterogeneities because it measures the formation response at discrete depths, not a bulk average. Another risk surfaces when contractors skip the Lugeon test in the shale transition zone. Under artesian conditions, an ungrouted rock socket becomes a vertical drain, destabilizing the base of a drilled shaft. The Lugeon profile, interpreted with Houlsby or Ewert criteria, tells the grouting engineer exactly where to inject and at what pressure. In Brampton’s industrial areas with a history of undocumented fill, we combine permeability testing with resistivity profiling to map zones of high moisture flux before the excavator breaks ground.
Applicable standards
ASTM D6391-11: Standard Test Method for Field Measurement of Hydraulic Conductivity Using Borehole Infiltration (Lefranc), ASTM D4630: Standard Test Method for Determining Transmissivity and Storativity of Low-Permeability Rocks by In-Situ Measurements Using the Constant-Head Injection Test (Lugeon reference), ASTM D5084: Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter (lab correlation), NBCC 2015, Division B, Part 4: requirements for geotechnical investigation including groundwater characterization, MTO Laboratory Testing Manual LS-702 (Ontario reference for hydraulic conductivity in earthworks)
Common questions
Does a Lefranc test in Brampton’s Halton Till give the same result as a lab permeability test on a Shelby tube sample?
Almost never. The Halton Till contains hairline fractures and occasional sand partings that a 75 mm Shelby tube cannot capture. A lab flexible-wall test measures the intact matrix K, often in the 10⁻¹⁰ m/s range, while a field Lefranc test integrates the mass permeability including secondary features. Field values are typically half an order to a full order of magnitude higher. For dewatering design, the field value is the one that governs.
How many Lugeon test intervals are needed for a typical Brampton high-rise excavation?
We recommend a minimum of three to five intervals per borehole that penetrates the shale contact. The first interval straddles the till-shale interface, and the remaining intervals step down in 2 to 3-meter increments. This spacing captures the weathered zone, which often shows elevated Lugeon values, and the competent rock below, where values drop below 3 Lu. The exact number depends on the socket depth required by the structural engineer.
What is the cost range for a field permeability test program in Brampton?
Can the Lefranc test be run in an existing monitoring well?
It is possible but not ideal. Monitoring wells with a long sand pack and screen introduce uncertainty about the tested zone. A dedicated Lefranc test in an open borehole with a short, isolated intake gives a far more reliable depth-discrete K value. If an existing well must be used, we recommend a falling-head slug test with a pressure transducer and the Bouwer-Rice analysis instead.
How long does it take to get the final permeability report?
Fieldwork for one borehole with two test intervals—one Lefranc and one Lugeon—takes four to six hours. The data reduction, Hvorslev or Lugeon analysis, and draft report are completed within three business days. If the project is on a fast-track schedule, we can deliver preliminary K values by email the same evening the test is completed.
