A mid-rise project on the Bedford Highway stopped dead in its tracks last fall. The excavator hit a pocket of fine gray silt at three meters. Nobody knew if it would drain or hold water. Turns out it was a marine clay layer, classic Halifax formation. The geotechnical report had missed it because the grain size analysis only ran a coarse sieve. That changed everything. Now we run the full hydrometer by default. In Halifax, where Lawrencetown till sits next to harbor mud, you cannot cut corners on particle distribution. We have learned to combine sieve stacks with sedimentation analysis for every borehole near the harbor. It is the only way to catch those sensitive silts before the footing goes in. When we prepare a grain size curve, we also triaxial test the same sample if the fines content exceeds 30 percent, because that silt can lose strength fast under load.
A missing hydrometer test in Halifax harbor silt can turn a routine excavation into a half-million-dollar dewatering nightmare.
Frequently asked questions
Why do I need both a sieve and a hydrometer test for a Halifax foundation?
The sieve alone only tells you the sand and gravel percentages. In Halifax, many soils contain a significant silt or clay fraction that passes the No. 200 sieve. That fine fraction controls drainage, frost heave, and long-term settlement. The hydrometer is the only way to measure it. Skipping it on a marine silt site can lead to a footing design that does not match the ground reality.
How much sample do you need for a complete grain size analysis?
We ask for about 500 grams of dry soil for a combined sieve and hydrometer run. For gravelly glacial tills from the Halifax area, we may need up to two kilograms to get a representative coarse fraction. We can work with bag samples or split-spoon samples from SPT drilling. The key is keeping the sample intact and not letting the fines dry out into hard lumps.
What is the typical cost for grain size testing in Halifax?
A combined sieve and hydrometer analysis in our Halifax lab ranges from CA$120 to CA$250, depending on whether it is a single sample or part of a larger geotechnical investigation package. The hydrometer test adds time because of the 24-hour sedimentation period. Rush turnaround is available at a premium.
How do I read the grain size distribution curve for my site?
The curve plots particle diameter on a logarithmic x-axis against percent passing on the y-axis. A steep curve means poorly graded soil, common in Halifax beach sands. A flat curve means well-graded material, typical of our glacial tills. The D10, D30, and D60 values let you calculate the uniformity coefficient and curvature coefficient. Those numbers tell you if the soil will compact well, drain freely, or trap water.
Does the test method change for marine clays versus glacial till?
The ASTM standards are the same, but the sample preparation changes. For marine clays from the Halifax harbor area, we dry the sample gently and use a mechanical disperser to break up the clay lumps without crushing the individual particles. For glacial till with a lot of coarse gravel, we run the full sieve stack first, then take only the minus-75-micron portion for the hydrometer. The two curves get mathematically combined into one continuous distribution.
