Field Permeability Testing (Lefranc & Lugeon) in Irving, TX

Select the Lugeon test when the investigation depth reaches competent rock, typically the Austin Chalk or intact Eagle Ford Shale found below 5 to 12 meters across Irving. The Lugeon procedure is designed for fractured rock where flow occurs primarily through discontinuities, and the five-pressure-stage sequence reveals whether fractures dilate, wash out, or close under injection pressure. The Lefranc test, by contrast, is appropriate for soil, weathered rock, and highly fractured material where the test zone can be flushed clean and does not require packer isolation against competent borehole walls. For the typical Irving stratigraphy, we frequently run Lefranc tests in the upper Taylor Marl and weathered transition zone, then switch to Lugeon once the driller confirms consistent rock recovery.

The Blackland Prairie clays of the Taylor Marl formation present several measurement challenges specific to Irving. These heavily overconsolidated clays contain polished slickensides and desiccation cracks that create preferential flow paths, meaning a Lefranc test in one borehole may yield a hydraulic conductivity value an order of magnitude different from a test just 10 meters away. The smectite content also causes borehole wall swelling during water injection, which can artificially reduce measured permeability over time. We mitigate this by using filtered, formation-compatible water and minimizing the test duration while still achieving steady-state flow conditions. Running replicate tests at multiple locations across the site provides a statistically meaningful range of values for dewatering design.

Lugeon values in the Austin Chalk beneath Irving range widely depending on fracture density and the presence of solution features. Intact chalk with tight, closed joints typically yields values between 1 and 5 Lu, while fractured and weathered zones near the top of the formation often exceed 15 Lu. We have recorded values above 30 Lu in intervals where karst-like dissolution channels have developed along bedding planes, particularly in areas closer to the Balcones fault zone influence. These high-permeability zones are the ones that cause dewatering system failures if not identified during the site investigation phase, and they also represent the intervals where cement grouting take can be significantly higher than estimated.

Field permeability testing in Irving typically ranges from US$680 to US$1,060 per test interval, depending on the depth, method, and number of pressure stages required. A single Lefranc test in a shallow borehole tends toward the lower end, while a full five-stage Lugeon test in deep rock with multiple packer setups and extended monitoring falls toward the upper end. Mobilization, drilling subcontractor costs, and data reporting are additional. Most Irving projects require between three and six test intervals to adequately characterize vertical permeability variation across the site, and we provide a detailed proposal after reviewing the geotechnical boring logs and project-specific groundwater concerns.