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Field Permeability Testing in Garland TX – Lefranc and Lugeon Methods

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Garland sits at roughly 551 feet above sea level, right on the edge of the Blackland Prairie where the soils tell a story of swelling clays and weathered shale. With a population pushing 250,000, the city has seen steady commercial and residential development, and nearly every project here eventually runs into the same headache: water. Understanding how water moves through the ground isn't a checkbox exercise—it's the difference between a dry basement and a flooded one, between a stable excavation and a costly collapse. The Lefranc and Lugeon field permeability tests give us that understanding directly from the subsurface, measuring hydraulic conductivity in soils and fractured rock. When you're dealing with the notorious Eagle Ford shale or the expansive Taylor clay common around Lake Ray Hubbard, guessing the drainage characteristics can backfire badly. A proper in-situ permeability test provides the data engineers need to design dewatering systems, retention ponds, and foundation drains that actually work for Garland's specific geology.

In Garland's expansive clay and shale, a single field permeability test can save more in dewatering costs than the entire geotechnical investigation budget.

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Methodology and scope

One mistake we see contractors make around Dallas County is treating all clay as impermeable and skipping the field test. The reality is that fissured clays and weathered shale zones can transmit surprising amounts of water, especially after heavy North Texas thunderstorms. We run the Lefranc test in soil and highly weathered rock, injecting or extracting water at a controlled head and measuring the flow rate to calculate the coefficient of permeability. In more competent fractured rock, we switch to the Lugeon method—a packer-isolated pressure test that tells you exactly how much water a fracture network can transmit under pressure. The data feeds directly into dewatering pump sizing, cut-off wall design, and even slope stability analyses. Our lab works under ASTM D6391 for the Lefranc procedure and follows the established Lugeon methodology refined by Houlsby, ensuring results that hold up when submitted to the City of Garland's Engineering Department or your geotechnical consultant.
Field Permeability Testing in Garland TX – Lefranc and Lugeon Methods
Technical reference — Garland

Local considerations

Garland's geology doesn't play by the textbook. The Eagle Ford shale formation, which underlies much of the city, is notorious for its unpredictable fracture patterns and variable weathering depth. You can hit hard, competent rock at 15 feet on one lot and completely weathered, soil-like shale at 40 feet on the next. When an excavation hits a water-bearing fracture zone that nobody tested for, the consequences cascade fast: slope raveling, base heave, and in the worst cases, a blowout that puts crews at risk. The IBC and local Garland amendments require groundwater control plans for excavations deeper than 8 feet, and the only way to build a defensible plan is with real hydraulic conductivity data from the field. Laboratory permeability tests on Shelby tube samples simply cannot capture the fracture flow or macro-porosity that dominates the real drainage behavior here. We've supported projects near Duck Creek and along the I-30 corridor where the field test revealed flow rates an order of magnitude higher than what remolded lab samples suggested—information that completely changed the dewatering approach.

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Reference standards

ASTM D6391 – Standard Test Method for Field Measurement of Hydraulic Conductivity Using a Borehole Infiltrometer (Lefranc Method), International Building Code (IBC) Chapter 18 – Soils and Foundations, ASCE 7 – Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Garland Code of Ordinances, Chapter 30 – Flood Damage Prevention, Houlsby, A.C. – Routine Interpretation of the Lugeon Water-Test (Quarterly Journal of Engineering Geology, 1976)

Technical data

ParameterTypical value
Test Method (Soil)Lefranc – Constant or Falling Head
Test Method (Rock)Lugeon – Packer-isolated pressure stages
Soil Types TestedClays, silts, sands, weathered shale
Rock Types TestedLimestone, shale, sandstone, fractured bedrock
Applicable StandardASTM D6391 (Lefranc) / Houlsby Method (Lugeon)
Typical Test Depth Range10 to 150 ft below grade
Reporting ParameterHydraulic conductivity k (cm/s or ft/day)
Turnaround TimePreliminary results within 48 hours

Frequently asked questions

When does the City of Garland require a field permeability test instead of a lab test?

The City of Garland typically follows IBC Chapter 18 requirements and the North Central Texas Council of Governments (NCTCOG) drainage criteria. Field permeability tests are generally required when designing stormwater infiltration systems, retention-detention ponds, or when dewatering is planned for excavations deeper than 8 feet. The Engineering Department wants to see in-situ hydraulic conductivity values—not just lab remolded tests—because the fractured shale and fissured clay common in Garland behave very differently in place than they do as disturbed samples. For infiltration-based stormwater BMPs, the design infiltration rate must be verified by field testing at the actual location and depth of the proposed facility.

¿Cuánto cuesta una prueba de permeabilidad Lefranc o Lugeon en Garland?

El costo varía según la profundidad, el número de intervalos de prueba y las condiciones de acceso. Para un programa típico en Garland con pruebas Lefranc a dos profundidades, el rango es de US$550 a US$990 por sondeo. Las pruebas Lugeon en roca, que requieren obturadores y múltiples etapas de presión, suelen ubicarse en el extremo superior de ese rango. La movilización del equipo de perforación se cotiza por separado y depende de la distancia dentro del área metropolitana de Dallas. Recomendamos solicitar una cotización específica para su proyecto, ya que las condiciones del subsuelo en zonas como Firewheel o el centro de Garland pueden requerir ajustes en el programa de pruebas.

How long does a field permeability test take on a Garland project site?

A single Lefranc test at one depth interval typically takes 60 to 90 minutes of active testing, not including drilling time to advance the borehole to the test depth. A full Lugeon test with five pressure stages in rock requires about 90 to 120 minutes per interval. For a typical Garland project with two or three test intervals per borehole, you should plan for one full day of field work per hole, including mobilization, drilling, testing, and grouting. We can often complete two shallow test holes in one day if site access and soil conditions cooperate—the Eagle Ford shale drills faster than the tough Austin Chalk further south.

Can the Lefranc test be run in the same borehole as an SPT investigation?

Yes, and that's standard practice on most Garland projects. We drill the borehole, perform the SPT at the required depth intervals per ASTM D1586, log the soil or rock, and then select the test zones for permeability based on what the stratigraphy shows. The same borehole serves both purposes, which saves you the cost of remobilizing a separate drilling crew. The key is isolating the test interval properly with a packer so that water doesn't short-circuit up the annulus—something we pay close attention to in the fissured clays and weathered shale that dominate Garland's subsurface.

Location and service area

We serve projects in Garland and surrounding areas.

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