Grain Size Analysis in Pickering: Sieve + Hydrometer Testing for Accurate Soil Classification

For a single sample processed through the full sieve stack plus hydrometer sedimentation, the cost ranges from CA$120 to CA$280 depending on whether the material is predominantly sand or contains a high clay fraction that requires extended sedimentation readings. Volume pricing applies for projects submitting five or more samples at once, which is common on subdivision earthworks contracts across north Pickering.

The Ontario Building Code, through its reference to the Canadian Foundation Engineering Manual, effectively requires hydrometer analysis whenever the fines content—particles passing the 0.075 mm sieve—exceeds 12 percent by mass. This threshold is critical for frost heave classification: soils with more than 10 percent finer than 0.02 mm by hydrometer are considered frost-susceptible and may require deeper footings or subgrade replacement in Pickering's climate zone.

A standard combined sieve and hydrometer analysis takes 48 hours in our Pickering lab. The hydrometer portion requires a minimum 24-hour sedimentation period for the clay fraction to settle properly—this cannot be rushed without compromising accuracy. For urgent cases, such as a ready-mix pour that needs aggregate gradation approval, we offer same-day sieve-only reporting if the sample arrives before 10:00 AM.

We require approximately 2 kilograms of material for a standard combined analysis, collected in a sealed plastic bag to preserve natural moisture. For gravelly soils, the sample should be larger—around 5 kilograms—so we have enough coarse fraction to run the full 75 mm through 4.75 mm sieve stack without bias. Samples taken from test pits or SPT split spoons are both acceptable, provided the bag is labelled with the project name, borehole number, and depth interval.

Sieve-only data can reliably classify clean gravels (GW, GP) and clean sands (SW, SP) where the fines content is visually confirmed to be below 5 percent. Once the percent passing the 0.075 mm sieve exceeds that threshold, the distinction between silty sand (SM), clayey sand (SC), and borderline silt (ML) becomes ambiguous without hydrometer data. In Pickering's glacial deposits, we frequently encounter sand with 8 to 15 percent fines that looks clean in the field but plots as SC after hydrometer testing—a difference that changes the allowable bearing pressure and the drainage design assumptions.