When you're working a site in Shreveport near the Red River, the difference between a routine soil report and a reliable hydrogeological model often comes down to how you measure mass permeability in situ. In our track record across Caddo Parish, lab permeameters on Shelby tube samples simply can't capture the secondary porosity from silt seams in the alluvial terrace deposits that dominate the local geology. For projects involving deep excavations, cutoff walls, or dewatering systems, we run the Lefranc test in boreholes above the water table and the Lugeon test in rock sockets below, giving us direct K values that reflect the real hydraulic behavior of the formation. This approach is particularly relevant when you're dealing with the Pleistocene terrace sands at depths between 15 and 40 feet, where layered permeability controls how fast your excavation floods. We often pair these results with a grain size analysis to validate the in-situ data against gradation curves, especially when those silty sand lenses show up unexpectedly in the boring logs.
In the Red River alluvium, a single Lugeon test in fractured claystone can reveal a 10x increase in permeability under just 3 bars of injection pressure—data you'll never get from a lab perm.
Process and scope
Site-specific factors
Shreveport's subsurface profile—Holocene overbank silts over Pleistocene terrace gravels, underlain by the Eocene Wilcox Group clays and lignite seams—creates a layered permeability regime that can surprise even experienced local contractors. The most costly mistake we see is assuming vertical downward flow when a horizontal sand lens at the excavation base connects to the Red River's fluctuating stage, turning a dry cut into a pumping nightmare overnight. In the Wilcox Formation, the presence of smectitic claystone with desiccation fractures means that a Lugeon test may show acceptable low permeability at 1 bar, but jump to 20 Lugeons at 3 bars once natural fissures open. This non-linear response has direct implications for cutoff wall depth and grout curtain design. The IBC Chapter 18 requires that design parameters for seepage be based on tests that replicate in-situ stress conditions; ignoring this and relying solely on particle-size empirical formulas like Hazen's can lead to dewatering system undersizing and OSHA excavation safety violations.
Standards used
ASTM D6391-11: Standard Test Method for Field Measurement of Hydraulic Conductivity Using Borehole Infiltration, IBC 2021 Section 1803.5.6: Groundwater table and seepage investigation requirements, USBR Design Standard No. 13, Chapter 8: Permeability Testing (Lugeon method for dam foundations)
Complementary services
Lefranc variable-head test
We install a temporary casing and isolate the test zone with a pneumatic packer in soil boreholes, then run a falling-head test in the saturated interval. This method is ideal for the interbedded sands and silts of the Red River terraces, providing K values for dewatering design, infiltration basin sizing, and contaminant transport modeling.
Lugeon packer test in rock
For dam abutments, bridge pier foundations socketed into the Wilcox Group, or deep tunnel alignments through the Cane River Formation, we execute five-stage pressure tests per USBR protocol. The test quantifies fracture flow, critical pressure for hydrojacking, and the groutability of the rock mass. Our crew uses a triple-packer system to test multiple intervals in one setup, reducing rig time.
Typical parameters
FAQ
What does a field permeability test cost in the Shreveport area?
For a single-interval Lefranc test in an existing borehole, you're typically looking at US$690 to US$890. A full five-stage Lugeon test in rock, including packer setup and pressure transducer data logging, runs between US$850 and US$1,050 per interval. Mobilization for sites outside the Shreveport metro adds a trip charge based on mileage from our local staging yard.
When is a Lugeon test required instead of a simpler Lefranc test?
A Lugeon test is the appropriate tool when you need to characterize hydraulic conductivity in fractured rock, particularly for dam foundation assessments, grout curtain design, or deep shafts where hydrojacking potential must be evaluated. The test applies stepwise pressure to distinguish between matrix flow and fracture flow. If your boring terminates in competent claystone of the Wilcox Group and you're only concerned about shallow dewatering in the overlying alluvium, a Lefranc test is sufficient.
Can you run the test in an existing monitoring well?
We strongly prefer to run Lefranc and Lugeon tests in an open borehole before well installation, because the gravel pack and screen slot geometry of a completed well introduce significant head losses that make the K value unreliable. If you have an existing well, we can perform a slug test as an alternative, but the data quality depends heavily on well development and screen placement relative to the target stratum. For critical design parameters, a dedicated test interval in a cored borehole is the benchmark.