Field Permeability Testing (Lefranc/Lugeon) in Boston

In the Back Bay, we see high groundwater levels perched on artificial fill. South Boston sits on thick Boston Blue Clay. The hydraulic contrast between these neighborhoods is extreme, and guessing the permeability coefficient is a costly mistake. A test pit can expose the soil profile visually, but it tells you nothing about how water moves through it. That is where the Lefranc test enters the picture. For bedrock, like the Cambridge Argillite found in the Seaport district, the Lugeon test becomes essential. The team runs these in-situ tests following ASTM D6391 to provide real permeability data for dewatering system design and basement waterproofing strategies.

A Lugeon value above 5 in Cambridge Argillite signals an open fracture network that can flood a deep excavation in minutes.

Process and scope

Back Bay's fill is loose and drains fast. Beacon Hill's glacial till is dense and slow. The Lefranc test captures these contrasts with a simple principle: a constant or falling head in a borehole. We isolate the test zone with a packer, avoiding cross-flow from overlying layers. In bedrock, the Lugeon test injects water under pressure in five stages to detect fracturing and dilation effects. The data feeds directly into a deep excavation dewatering plan. For glacial till sites, we often combine this with a grain-size analysis to correlate field permeability with the coefficient of uniformity. The procedure is straightforward, but the interpretation requires understanding Boston's complex glacial history.

Site-specific factors

The most common error in Boston is using textbook permeability values for Boston Blue Clay. The intact marine clay has a very low vertical permeability, but the weathered crust and sand lenses within it conduct water. A contractor who skips the in-situ test will undersize the dewatering system. The excavation floods. The sides slump. On bedrock jobs, assuming a 'tight' Cambridge Argillite without a Lugeon test is another classic failure mode. A single open joint with a Lugeon value of 10 Lu can produce inflows exceeding 100 gpm. The grouting program then becomes a reactive emergency instead of a planned phase. The data from these tests defines the maximum drawdown and the pumping rate for the MassDEP groundwater discharge permit.

Technical data

Parameter	Typical value
Test Method	Lefranc (constant/falling head) in soil; Lugeon (pressure test) in rock
Applicable Standard	ASTM D6391-11 (reapproved 2020)
Soil Application	Granular fills, glacial till, organic silt, Boston Blue Clay
Rock Application	Cambridge Argillite, Roxbury Conglomerate, Dedham Granite
Measured Parameter	Hydraulic conductivity k (cm/s) or Lugeon unit (Lu)
Test Interval	Typically 1.0 to 5.0 meters isolated with pneumatic packers
Pressure Stages (Lugeon)	5 stages: Pmax, Pmin, Pmax, Pmed, Pmax per Houlsby method
Reporting Format	Log of k vs depth, Lugeon vs pressure plots, flow profile

Complementary services

Lefranc Testing in Overburden

Constant-head and falling-head tests in boreholes through fill, till, and varved clays. We use pneumatic packers to isolate specific layers and measure hydraulic conductivity directly.

Lugeon Testing in Bedrock

Five-stage pressure tests in rock cores to determine fracture permeability. We apply the Houlsby method to differentiate between laminar flow, turbulent flow, dilation, and washout.

Dewatering Flow Analysis

Calculation of steady-state inflow rates for excavation support systems. We combine the k-value from field tests with the Dupuit or Theis equations to size wellpoints and deep wells.

Questions and answers

What is the difference between the Lefranc and Lugeon tests?

The Lefranc test measures hydraulic conductivity in soil by introducing water into a borehole section under a constant or falling head. The Lugeon test applies water under pressure in fractured rock to assess joint permeability. We use Lefranc for overburden and Lugeon for bedrock.

How much does a field permeability test cost in Boston?

The cost for a Lefranc or Lugeon test program typically ranges from US$610 to US$980 per test interval, depending on depth, number of stages, and mobilization requirements within the greater Boston area.

Why is the Lugeon test done in five pressure stages?

The five-stage sequence (low, medium, high, medium, high) reveals how the rock fracture network behaves under pressure. A steady increase in flow indicates laminar flow. A sharp jump at high pressure suggests fracture dilation or washout, which affects the grouting strategy.

Can you test permeability in Boston Blue Clay?

Yes. While the intact clay has very low hydraulic conductivity, we test the weathered crust and any silt or sand seams within the clay. A Lefranc test in these zones provides critical data for estimating leakage into deep excavations.