Grain Size Analysis (Sieve + Hydrometer) in Thunder Bay

The glacial lake clays around Thunder Bay hold water like a sponge. When saturated, these fine-grained deposits shift their behavior entirely. A standard compaction test alone won't tell you what you need. The grain size curve from a full sieve and hydrometer analysis according to ASTM D422 reveals the silt and clay fractions controlling permeability and frost action. On the city's north side, where the Superior shoreline meets compact till, the distribution changes meter by meter. We run the full stack: wash sieving for the coarse fraction, hydrometer for the fines, and a test pits log to tie the sample to its exact stratum. Without this data, drainage design on the Kam River floodplain is just a guess.

A single hydrometer reading on Thunder Bay varved clay can predict frost heave potential better than three boreholes without gradation.

Process and scope

Thunder Bay's geotechnical reality is shaped by proglacial Lake Agassiz sediments. The CSA A23.3 standard for concrete aggregates requires strict compliance on gradation. Our lab runs the ASTM D6913 sieve procedure plus ASTM D7928 hydrometer analysis to cover the full spectrum from gravel to colloidal clay. For frost-susceptibility classification under MTO and City of Thunder Bay standards, the percent passing 0.075 mm is non-negotiable. When that number exceeds 15 percent, the material is frost-susceptible. Period. On Rosslyn Road industrial projects, we often pair this with in-situ permeability tests to confirm that the laboratory gradation translates to field hydraulic conductivity in the silty sand lenses common to the area.

Site-specific factors

The Intercity area's expansion in the 1960s pushed development onto compressible silty clays with low plasticity. Early foundations here sometimes lacked proper gradation context. The risk is real: a soil classified visually as sandy silt can still have 40 percent clay content, leading to differential settlement under cyclic loading from heavy rail traffic near the waterfront terminals. A hydrometer test catches that. The coefficient of uniformity (Cu) and coefficient of curvature (Cc) from the full curve determine whether the material is well-graded or gap-graded, which directly impacts filter design for retaining structures near the Neebing River. Misclassifying a gap-graded silty sand as well-graded has caused more than one drainage failure in this city.

Reference parameters

Parameter	Typical value
Test standard (full curve)	ASTM D422 / D6913 + D7928
Sieve range	75 mm to 0.075 mm (No. 200)
Hydrometer range	0.075 mm to 0.001 mm
Minimum sample mass (fine)	200 g (ASTM D7928, Method B)
Hydrometer type	152H
Dispersing agent	Sodium hexametaphosphate
Reporting	D10, D30, D60, Cu, Cc, % gravel, sand, silt, clay

Related services

Complete ASTM D422 Sieve and Hydrometer Package

Covers the full range from gravel to clay. We process the sample through wash sieving, mechanical dry sieving, and a 24-hour hydrometer sedimentation analysis. The resulting report includes the gradation curve, D-values, and USCS classification.

Frost-Susceptibility Gradation Screening

Focused on the critical 0.075 mm sieve threshold per local municipal standards. We quantify the silt and clay fraction to classify the material as frost-susceptible (F1-F4). Essential for pavement subgrade and shallow utility bedding design in Thunder Bay's 1.8 m frost depth zone.

Applicable standards

ASTM D422 Standard Test Method for Particle-Size Analysis of Soils, ASTM D6913 Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis, ASTM D7928 Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis, CSA A23.1 Concrete Materials and Methods of Concrete Construction, MTO LS-702 Determination of Particle Size Distribution of Soils

Common questions

What does a grain size analysis cost for a Thunder Bay project?

A full ASTM D422 sieve and hydrometer test package typically runs between CA$120 and CA$260 per sample, depending on the number of samples and whether organic content or specific gravity determination is also required.

How long does the hydrometer test take in the lab?

The sedimentation phase takes a minimum of 24 hours, as readings are logged at specific intervals per ASTM D7928. Including sieve preparation, the full report is available within 3 to 5 business days.

Why is the 0.075 mm fraction so critical in Thunder Bay soils?

The percent passing the No. 200 sieve controls frost susceptibility. The silty matrix of the glaciolacustrine deposits here often exceeds 15 percent fines, placing them in the F3 or F4 category. This requires special subgrade treatment or insulation to prevent frost heave under pavements and shallow foundations.