SPT (Standard Penetration Test) in Saguenay

The Saguenay basin sits on a deep sequence of post-glacial marine clays, the famous Laflamme Sea sediments, often reaching 60 meters before hitting till or rock. Anyone who has drilled near the Chicoutimi riverbanks knows the interbedded silts can fool you — stiff at the spoon but highly sensitive when remolded. We run our SPT program with that exact sensitivity in mind, because blow counts alone don't tell the full story in these Champlain Sea-type deposits. A good split-spoon recovery paired with our lab's index testing — Atterberg limits run the same day — quickly flags the difference between a competent silt and a quick clay that could spell trouble for footings. With Saguenay sitting in a moderate seismic zone (NBCC 2020 zone with Sa(0.2) around 0.4-0.5 g), the SPT data feeds directly into liquefaction screening and site class determination per the National Building Code.

An N-value without the energy correction is just a number — with ASTM D1586-18 calibration, it becomes an engineering parameter for Saguenay's sensitive clays.

Scope of work

A mistake we see too often on Saguenay projects is logging an SPT without measuring the actual hammer energy. The old safety hammers on CME rigs can deliver anywhere from 40 to 80 percent of theoretical energy depending on the cathead setup, and if you don't correct for that, your N60 can be off by a factor of two. We run every SPT borehole with ASTM D1586-18 procedures and an energy calibration record — no exceptions. The field kit includes a 140 lb hammer dropping 30 inches, a standard split-spoon sampler with the liner intact, and the drive counted over three 6-inch increments. The N-value is the sum of the last two increments, and we log the first separately as seating drive. In our experience, the stiff desiccated crust in the Jonquière area often gives N-values above 30 in the first 2 meters, then drops to single digits in the soft clay below — if you stop the borehole too early, you miss the weak layer that controls settlement. Each SPT sample bag gets sealed and matched to the depth log, so the grain-size distribution and fines content are always traceable to the exact blow count profile.

Area-specific notes

Saguenay sits about 160 kilometers up the fjord from the St. Lawrence at an elevation range from near sea level at La Baie to over 150 meters on the terraces. That topography creates groundwater conditions that vary dramatically across short distances — a borehole on one lot might hit the water table at 2 meters while the neighbor's basement stays dry year-round. In the 1988 Saguenay earthquake (M5.9), the soft clay deposits in the lowlands amplified ground motion significantly, and areas near the Chicoutimi and Saguenay rivers saw slope failures and lateral spreads in the sensitive marine clays. SPT data from those post-quake investigations still inform our liquefaction screening today — we use the Seed-Idriss simplified procedure with N60 values to estimate cyclic resistance ratios, and we know from firsthand observation that fines content in these clays pushes the CRR curve upward. If your site is within 500 meters of a riverbank or on a terrace edge, skipping the SPT means you are blind to the potential for flow liquefaction in a deposit that looks perfectly stable at the surface.

Reference parameters

Parameter	Typical value
Hammer type	Automatic trip, 140 lb (623 N) with energy calibration record
Drop height	30 inches (762 mm) per ASTM D1586-18
Sampler	Standard split-spoon, 2-inch OD, 1.375-inch ID, with liner
Drive increments	Three 6-inch (150 mm) increments; N = sum of last two
Seating drive	First 6-inch increment logged separately per ASTM protocol
Borehole diameter	4 to 8 inches (100-200 mm), depending on casing requirements
Sample recovery	Measured and reported as percentage per interval
Energy correction (N60)	Corrected to 60% of theoretical free-fall energy

Linked services

Energy-Calibrated SPT Drilling

Boreholes advanced with hollow-stem auger or mud rotary in Saguenay's clay-silt-till sequence, with automatic trip hammer and ASTM D1586-18 energy measurement on every project.

Liquefaction Screening Package

N60 values corrected for overburden and energy, paired with fines content from wash sieving, run through Seed-Idriss simplified procedure for NBCC site class determination.

Bearing Capacity and Settlement Analysis

SPT N60 correlations to undrained shear strength in clays and relative density in granular layers, with settlement estimates using Schmertmann or Burland-Burbidge methods.

Standards used

ASTM D1586-18 — Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils, NBCC 2020 — National Building Code of Canada, seismic provisions and site classification, CSA A23.3 — Design of Concrete Structures, reference for geotechnical input parameters, Youd & Idriss (2001) — NCEER Workshop on Evaluation of Liquefaction Resistance, Seed & Idriss (1982) — Ground Motions and Soil Liquefaction During Earthquakes

Quick answers

How much does an SPT investigation cost for a typical Saguenay residential lot?

For a single-family residential project in the Saguenay area, a basic SPT program with one borehole to 10-12 meters depth, energy calibration, and lab testing on selected samples typically ranges from CA$800 to CA$910. The final number depends on access conditions, depth to refusal, number of samples sent to the lab, and whether we need to install a monitoring well.

What depth do you typically drill for SPT in the Saguenay clay belt?

In the Laflamme Sea clay deposits that dominate the Saguenay lowlands, we usually target 15 to 25 meters depth, or until we hit competent till or bedrock. The NBCC 2020 site classification requires shear wave velocity or SPT data over the top 30 meters, so if the project is a multi-storey building, we extend to 30 meters. The stiff crust in the Jonquière-Chicoutimi corridor often delays the soft clay until 4-6 meters, so stopping at 8 meters can completely miss the critical layer.

How do you handle SPT in the quick clays we have in the region?

Sensitive marine clays — the so-called quick clays — are common in the Saguenay basin, and the SPT procedure itself can remold them if we are not careful. We use thin-walled Shelby tubes alongside the split-spoon to recover undisturbed samples for lab testing, and we log the SPT blow counts with notes on sample disturbance. The key is comparing field vane shear strength with the N60 correlation: if the SPT overestimates strength in a high-sensitivity clay, the lab Atterberg limits and sensitivity measurements tell us by how much. That information is critical for slope stability work and any excavation near the river.

SPT (Standard Penetration Test) in Saguenay — Field Data from the Fjord