Grain Size Analysis (Sieve + Hydrometer) in Winnipeg

Winnipeg sits on the bed of ancient Lake Agassiz. A full 12 meters of fat lacustrine clay blankets much of the city. That clay dictates everything about your foundation. Standard sieve analysis misses the fines. You need the hydrometer too. Our lab runs the full ASTM D422/D6913 suite. We see silts from the Assiniboine floodplain every week. We see tills from the Birds Hill esker. Grain size distribution determines frost susceptibility. It controls drainage design. It predicts swelling potential. Miss the clay fraction and your retaining wall fails. It's that simple. For deep foundations in the clay belt, we often pair grain size with liquefaction screening when silts are present below the water table.

If your grain size curve stops at the No. 200 sieve in Winnipeg clay, you just ignored the most reactive 40% of your soil.

Methodology and scope

CSA A23.3 references ASTM D422 for concrete aggregate gradation. But we go further. Our Winnipeg lab runs sieve stacks from 75 mm down to 75 microns. Then the hydrometer takes over. We measure specific gravity per ASTM D854. Temperature correction is critical here. The lab sits at 238 meters elevation. Barometric pressure affects readings. We use sodium hexametaphosphate as dispersant. The hydrometer settles for 24 hours minimum. We log readings at 0.5, 1, 2, 4, 8, 15, 30, 60 minutes then 4 and 24 hours. This catches the 2-micron clay fraction. The old Winnipeg building code missed this. Now engineers demand it. A full curve from gravel to colloids tells you the soil's story. You see gradation gaps. You see uniform sands. You see gap-graded tills. Each one behaves differently under load. Each one drains differently. We flag anything outside the envelope immediately.

Local considerations

The biggest mistake we see is contractors using a simple wash-sieve and calling it done. You get sand and gravel percentages. That's it. The remaining fines go down the drain. In Winnipeg's Lake Agassiz clay, those fines are pure smectite. They swell 30% when wet. Your foundation heaves. Your slab cracks. Your basement leaks. A proper hydrometer test catches this. Another common error is dry sieving sticky clay. The lumps won't break. You get false coarse readings. We wet-sieve everything first. The wash water carries fines to the hydrometer cylinder. Nothing is lost. Frost heave design under NBCC requires the silt-clay split. Guess wrong and your frost wall is undersized. The soil freezes. The ice lens grows. The structure moves. In Winnipeg, frost penetrates over 2 meters deep. The grain size curve is your first line of defense against heave.

Technical parameters

Parameter	Typical value
Sieve range	75 mm to 75 µm (No. 200)
Hydrometer range	75 µm to 1 µm (clay colloids)
Standard	ASTM D422 / D6913 / D7928
Sample mass	500 g minimum (fines-rich), up to 50 kg for gravels
Dispersant	Sodium hexametaphosphate (NaHMP)
Hydrometer type	ASTM 152H, calibrated at 20°C
Reported parameters	D10, D30, D60, Cu, Cc, % gravel, sand, silt, clay
Turnaround	3 business days standard, 24-hour rush available

Associated technical services

Combined Sieve + Hydrometer

Full curve from 75 mm gravel down to 1 micron clay. Includes D-values, Cu, Cc, and USDA or USCS classification. Standard report with gradation chart.

Wash Sieve Analysis

For clean sands and gravels where fines content below 5% is expected. Wet washing through No. 200 sieve. Dry sieve of retained fraction. Fast turnaround.

Hydrometer-Only Analysis

For fine-grained soils passing the No. 200 sieve. 24-hour sedimentation test with full Stoke's Law calculations. Required for frost heave susceptibility classification.

Aggregate Gradation for Concrete

Per CSA A23.2-2A. Combined coarse and fine aggregate gradation. Check against CSA A23.1 limits for Winnipeg ready-mix and precast applications.

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, ASTM D854 Specific Gravity of Soil Solids, CSA A23.1/A23.2 Concrete Materials and Methods (aggregate gradation reference)

Frequently asked questions

How much sample do you need for a combined sieve and hydrometer test in Winnipeg clay?

For typical Lake Agassiz clay with high fines, 500 grams of air-dried material passing the No. 4 sieve is sufficient. If gravel is present, we need up to 5 kg total to run the coarse sieve stack properly. For aggregate gradation per CSA, 10 kg minimum for 20 mm nominal size.

What does a grain size analysis cost in Winnipeg?

A combined sieve and hydrometer test typically ranges from CA$130 to CA$270 depending on sample complexity. A wash-sieve only runs at the lower end. Full hydrometer with specific gravity is at the upper end. Volume discounts apply for 10+ samples.

How long does the hydrometer test take to run?

The sedimentation portion runs 24 hours minimum per ASTM D7928. We take readings at specified intervals over that period. Total lab turnaround including oven-drying, sieve analysis, and reporting is 3 business days. Rush service delivers in 24 hours for an additional fee.

Why does Winnipeg clay need a hydrometer instead of just sieves?

Winnipeg sits on glacial Lake Agassiz deposits. The clay fraction often exceeds 60% and includes swelling smectites. A sieve stack stops at 75 microns and misses everything finer. The hydrometer captures particles down to 1 micron. This clay fraction controls frost heave potential, swelling pressure, and drainage behavior. Without it, your geotechnical design is guessing.