ASTM D4630 provides the framework, but Philadelphia's geology demands a tailored approach to field permeability testing. The city straddles the Fall Line where the crystalline bedrock of the Piedmont meets the unconsolidated sediments of the Atlantic Coastal Plain. This transition creates hydraulic conductivities that can vary by orders of magnitude across a single project site. A Lefranc test in the weathered Wissahickon Schist south of Chestnut Hill often yields results that bear no resemblance to a Lugeon test conducted in the fractured gneiss near Manayunk. Our ISO 17025 accredited laboratory executes these in-situ determinations because dewatering volumes, cutoff wall depths, and grouting programs hinge on data collected directly from the formation, not from remolded samples shipped to a bench. Integrating these results with a CPT investigation often clarifies stratigraphic boundaries where packer seating is critical.
A single Lugeon test in fractured Wissahickon Schist can reveal more about groundwater flow paths than a dozen lab permeameter tests on intact core samples.
Scope of work in Philadelphia
Local geotechnical conditions in Philadelphia
Philadelphia's Wissahickon Schist weathers into a saprolite mantle that retains the fabric of the parent rock but behaves hydraulically like a silty sand. Depth to bedrock can shift from 10 feet to over 60 feet within a city block, particularly near the old stream valleys now buried beneath Center City streets. A Lugeon test placed too high in the transition zone risks bypass flow around the packer, yielding a falsely high permeability that could lead to gross underestimation of grout quantities. Conversely, running a Lefranc test in a borehole without adequate filter cake removal produces a smeared zone that can drop apparent conductivity by an order of magnitude. The IBC 2021 references ASCE 7-22 for design parameters that tie directly to subsurface drainage characteristics, making the accuracy of these in-situ values a structural safety concern.
Our services
The field permeability testing program is structured to provide design-ready hydraulic parameters for dewatering, grouting, and foundation drainage.
Lefranc Testing in Soil
Variable and constant-head tests in soil and highly weathered rock using a cased borehole with a screened test section. Delivers point hydraulic conductivity per ASTM D6391.
Lugeon Testing in Bedrock
Pneumatic packer isolation of discrete intervals in competent rock. Five-stage pressure testing with real-time flow monitoring to determine Lugeon values and fracture flow regimes.
Dewatering & Grouting Parameter Reports
Interpretation of pressure-flow curves, calculation of equivalent hydraulic conductivity, and recommendations for well spacing, pump sizing, or grout mix design based on in-situ results.
Frequently asked questions
When should a Lugeon test be specified instead of a Lefranc test?
A Lugeon test is the appropriate method when the formation is rock with fracture-controlled permeability. The test uses a packer to isolate a section of the borehole and measures water take under pressure. In Philadelphia, this applies to the Wissahickon Schist and Chickies Quartzite found below the soil mantle. A Lefranc test, by contrast, is designed for soil or intensely weathered rock where a screen and sand pack are used.
How long does a typical field permeability testing program take?
Mobilization and test execution depend on depth and the number of intervals. A single Lefranc test in a 30-foot borehole through the Trenton Gravel may be completed in under two hours. A multiple-interval Lugeon test program in a 100-foot bedrock hole with five test stages per interval typically requires a full day to allow for packer inflation, pressure stabilization, and flow equilibration at each depth.
What is the typical cost range for field permeability testing in Philadelphia?
For a standard program involving a combination of Lefranc and Lugeon testing, project costs generally range from US$610 to US$1,060. The final figure reflects the number of test intervals, depth of investigation, and the complexity of pressure step interpretation required by the project geotechnical engineer.
How do you ensure a valid Lugeon test in fractured Wissahickon Schist?
We verify packer seating above a competent section of the borehole, then run a five-stage pressure cycle (low, medium, high, medium, low) to assess fracture dilation, washout, and flow regime. The pressure-flow curves are plotted in real time. A non-linear curve indicating turbulent flow or fracture jacking is interpreted using the Houlsby method, and the test is repeated if packer bypass is suspected.