Norfolk's urban fabric, from its historic Ghent district to the burgeoning waterfront developments along the Elizabeth River, rests upon a geological foundation shaped by millennia of fluctuating sea levels. The city's average elevation of just seven feet above mean sea level means that any significant excavation or foundation work immediately contends with the shallow, unconfined aquifer of the Atlantic Coastal Plain. In our experience supporting geotechnical investigations across Hampton Roads, the most frequent challenge isn't the bearing capacity of the deeper Yorktown Formation sediments, but rather the hydraulic conductivity of the overlying Pleistocene-age sands and interbedded silts. A CPT test can provide a continuous profile of soil behavior type, yet quantifying the rate at which groundwater will flow into an excavation demands a direct, in-situ measurement. The field permeability test, specifically the Lefranc and Lugeon methodologies, bridges this gap by measuring the soil mass's hydraulic conductivity under natural or controlled stress conditions, delivering the empirical data engineers require to design effective dewatering systems and predict settlement timelines.
In Norfolk's shallow water table, a Lugeon value of less than 1 Lu often indicates a stratum suitable for a natural seal, while values exceeding 15 Lu demand solid active dewatering plans.
How we work
Local ground factors
A recent mid-rise mixed-use project on Hampton Boulevard encountered a scenario that underscores the critical nature of this testing. The geotechnical baseline report assumed a relatively homogeneous, medium-dense sand with a permeability of 1x10^-3 cm/s, based on index testing alone. However, during the excavation for a two-level parking garage, the contractor hit a buried paleochannel filled with very loose, coarse sand and gravel—a relic of an ancient tributary of the Lafayette River. The actual inflow rates were nearly forty times greater than the original dewatering design anticipated, leading to significant schedule delays and the emergency installation of additional deep wells. A pre-construction Lugeon profile, performed with a slope stability analysis for the adjacent embankment, would have identified the anomalous high-permeability zone and allowed for a more solid, layered dewatering strategy. In Norfolk, where the stratigraphy is riddled with these hidden depositional features, skipping field permeability testing is a gamble that turns a predictable construction cost into an open-ended liability.
Regulatory framework
ASTM D6391 - 11: Standard Test Method for Field Measurement of Hydraulic Conductivity Using Borehole Infiltration, IBC Chapter 18: Soils and Foundations, USACE EM 1110-2-1901: Seepage Analysis and Control for Dams, ISRM Suggested Method for Lugeon Test
Related services
Variable Head and Pressure Injection Testing
We perform both falling/constant-head Lefranc tests in granular soils and multi-stage Lugeon tests in cemented or fractured materials. The Lugeon method is executed in five pressure steps to evaluate the flow regime (laminar, turbulent, dilation, or washout), providing insight into fracture network behavior that a single-point test cannot capture.
Integrated Hydrogeological Profiling
By combining the field permeability data with soil stratigraphy from SPT drilling logs and particle size distributions, we generate a detailed vertical profile of hydraulic conductivity. This profile directly informs the design of dewatering well screens, the calculation of seepage forces for excavation stability, and the environmental assessment of contaminant transport pathways.
Typical parameters
Quick answers
When is a Lugeon test preferred over a Lefranc test in Norfolk?
The Lugeon test is the preferred method when the investigation encounters fractured or weathered rock, cemented sands, or shell hash layers—conditions not uncommon in the deeper portions of the Norfolk formation. Because it uses a double packer and applies staged pressures, the Lugeon test can differentiate between laminar flow through tight joints and turbulent flow through open fractures, which is essential for designing grout curtains or evaluating rock mass permeability for deep excavations.
What is the typical cost range for a field permeability test in Norfolk?
For a single Lefranc or Lugeon test interval in the Norfolk area, the cost typically ranges from US$650 to US$1,160. The final price depends on the depth of the test zone, the number of pressure stages required, and the complexity of the borehole setup, including any necessary drilling through overlying layers.
How does the shallow water table in Norfolk affect the test procedure?
The high water table, often just 3 to 5 feet below grade, simplifies the saturation of the test zone but demands strict control of the borehole seal. Any leakage along the casing or through an inadequately sealed bentonite plug can short-circuit the test, giving a falsely high permeability reading. We typically use a pneumatic packer and carefully monitor the annular space to ensure the measured flow is exclusively from the test interval.
Which ASTM standard governs the Lefranc permeability test in the USA?
ASTM D6391-11 is the standard test method for field measurement of hydraulic conductivity using borehole infiltration, which covers the Lefranc constant-head and falling-head procedures. For the Lugeon test, while there is no direct ASTM standard, the methodology follows the ISRM Suggested Methods and is referenced within the broader framework of ASTM D4630 for rock mass characterization.