Field Permeability Testing (Lefranc & Lugeon) for Saguenay...

Saguenay’s development, shaped by the 1996 deluge and its legacy of hydroelectric infrastructure, places a singular emphasis on understanding groundwater. The city, carved through the Precambrian Shield and mantled with glacial and marine clays, sits on terrain where a misjudged permeability value can cascade into catastrophic delays. For the Shipshaw or Chute-à-Caron sectors, our team performs field permeability testing that isolates fractures and soil horizons with the precision required by CSA and ASTM standards. Whether dealing with deep foundations near the Rivière Saguenay or assessing a new industrial site in Jonquière, the Lefranc test in soils and the Lugeon test in rock provide the direct hydraulic conductivity measurements that lab tests simply cannot replicate. We integrate this data with in-situ permeability correlations when site access constrains drilling, ensuring every report reflects the complex hydrostratigraphy typical of this region.

In the Saguenay graben, a single Lugeon stage in fractured gneiss can differentiate between a tight abutment and a grout-intensive curtain requirement.

Scope of work

The most common error we see on Saguenay projects is substituting grain-size-derived permeability estimates for actual field tests in the sensitive Laflamme Sea clays. These silty clays, particularly in the lowlands of Chicoutimi and La Baie, exhibit macroporosity from root channels and desiccation cracks that triples the true in-situ conductivity. A design based solely on a textbook Hazen correlation will underestimate inflow to excavations and overestimate the effectiveness of dewatering systems. We avoid this by deploying the falling-head Lefranc method at multiple packer-isolated intervals within the same borehole, capturing the vertical variation between the oxidized crust and the intact grey clay below. For rock mass characterization in the charnockitic gneiss typical of the surrounding highlands, the Lugeon pattern—five pressure steps per stage—reveals whether fractures dilate or clog under pressure, a critical insight often missed when combining this test with a standard cpt test in overburden soils.

Area-specific notes

NBCC 2015 and CSA A23.3 mandate that foundation design account for groundwater conditions, a requirement that becomes non-negotiable in Saguenay’s post-glacial clays with their metastable structure. The 1988 earthquake demonstrated how pore-pressure buildup can trigger flow slides in the sensitive marine deposits along the Rivière-aux-Sables. Ignoring field permeability data means a retaining wall or deep excavation support system designed for drained conditions could face undrained failure during a rapid drawdown event. In the crystalline bedrock of the Saguenay Highlands, an ungrouted dam foundation with undetected open joints—joints that a Lugeon test would flag as fully open (Lu > 20)—risks internal erosion of the overlying till blanket. This isn't speculative; we have observed grout takes exceeding 500 kg/m in such fractures, directly correlating to high Lugeon values measured during our pre-grouting investigations.

Reference parameters

Parameter	Typical value
Test Standard (Soil)	ASTM D4630 / CSA A23.3 guidance
Test Standard (Rock)	ASTM D4630 / USBR 6510 (Lugeon)
Test Interval (Lefranc)	0.5 to 1.5 m typical, isolated by packers
Pressure Steps (Lugeon)	5-step cycle: Pmin–Pmax–Pmin
Permeability Range	10^-7 to 10^-2 cm/s (soil); 10^-1 to 100 Lugeon units (rock)
Borehole Diameter	NQ to HQ (rock); 100–200 mm (soil)
Reporting Parameter	k (cm/s) or Lugeon value (Lu) per interval

Linked services

Lugeon Packer Testing in Rock

Multi-stage pressure testing in NQ/HQ boreholes through the Precambrian gneiss and anorthosite. We quantify joint condition (open, dilated, clogged) and calculate representative Lugeon values for grouting design and curtain effectiveness verification.

Lefranc Variable-Head Tests

Falling-head and constant-head tests in soil boreholes using slotted casing and gravel packs. Ideal for characterizing the hydraulic conductivity of Saguenay’s littoral sands and the weathered till layer above bedrock.

Piezometer Installation & Monitoring

Standpipe and vibrating-wire piezometer installations in sealed borehole sections. Long-term monitoring of phreatic levels and artesian pressures in the confined aquifer systems found beneath the Chicoutimi terrace.

Dewatering & Seepage Analysis Support

Integration of field k-values into 2D/3D seepage models (SEEP/W, MODFLOW) to size dewatering systems for excavations in the marine clay plains and to evaluate cutoff wall requirements near the Saguenay River.

Quick answers

What is the typical cost range for a field permeability test program in Saguenay?

For a standard investigation including Lugeon testing in rock or Lefranc tests in soil, project costs typically range from CA$750 to CA$1,600 per day, depending on mobilization distance, the number of test intervals, and packer setup complexity. A full program with multiple boreholes and piezometer installations will scale accordingly.

When should we specify a Lugeon test instead of just relying on RQD and fracture counts?

RQD tells you about core recovery, not hydraulic conductivity. In the fractured bedrock of the Saguenay region, a tightly jointed gneiss can have RQD > 80% but still transmit significant flow through a single open discontinuity. Specify a Lugeon test whenever a dam foundation, tunnel alignment, or deep excavation requires a quantitative assessment of rock mass permeability for grouting or dewatering design.

How does the Lefranc test in Saguenay’s clays differ from a standard falling-head test in sand?

In the sensitive clays, we must use very low hydraulic gradients to avoid disturbing the soil structure during testing. Unlike a quick test in sand, the Lefranc test here often requires extended observation periods to reach a pseudo-steady state, and we use smaller-diameter standpipes to minimize storage effects. The result is a k-value that reflects the intact, unfractured clay matrix rather than an artificially enhanced value from hydraulic fracturing.

Field Permeability Testing (Lefranc & Lugeon) for Saguenay Geotechnical Projects