Our team sets up the full sieving and sedimentation train in the Calgary lab using a Gilson SS-15 sieve shaker and a series of ASTM E11 sieves from 75 mm down to 0.075 mm. For the fine fraction we run the hydrometer analysis in a temperature-controlled bath at 20°C. The entire process follows ASTM D6913-17 for coarse-grained soils and ASTM D7928-17 for the silt-clay portion. Before any classification we always check the sample mass against the minimum required by the standard — for a 50 mm maximum particle size you need at least 20 kg of dry material. The final USCS group symbol and AASHTO group index come from the grain-size curve combined with Atterberg limits from the fraction passing the No. 40 sieve.
Calgary glacial till falls between ML and CL groups; AASHTO A-4 to A-6 with group index between 4 and 12 depending on the fines content.
Methodology and scope
Calgary sits on a complex mix of glacial till, lacustrine clays and fluvial gravels from the Bow and Elbow river terraces. The till here has a bimodal grain-size distribution typical of lodgment till — high silt fraction in the matrix with occasional cobbles — so the standard USCS classification often falls into ML or CL groups. For highway embankments and subgrades we combine the classification with a CBR vial assessment to evaluate bearing capacity under soaked conditions, and we always cross-check the AASHTO group index with the límites de Atterberg to detect swelling potential in the Bearspaw shale zones. The cold semi-arid climate means freeze-thaw cycles can alter the gradation of the upper 1.5 m, so we classify samples from below the frost line or specify the seasonal moisture correction per CFEM (Canadian Foundation Engineering Manual).
Technical reference image — Calgary
Local considerations
Calgary has a population of 1.3 million and sits at 1,045 m elevation in a seismic zone classified as moderate (NBCC 2020 PGA 0.16g). The thick glacial till sequences can mask liquefiable sand lenses up to 3 m thick that only appear when you perform a full soil classification with hydrometer analysis. Without the USCS group symbol and the fines content above 35%, those lenses get missed in routine logging. We always run the full classification on every borehole sample from the river valley areas — the Elbow Park and Inglewood neighborhoods have documented cases of differential settlement linked to undocumented silt layers that only showed up in the hydrometer curve.
152H with ASTM 152H scale, Meniscus correction applied
Atterberg limits
Liquid limit (LL), plastic limit (PL), plasticity index (PI) per CSA A23.2-2A
AASHTO group index
Ranges from 0 (granular) to 20+ (clayey subgrade)
Sample mass required
20 kg for max particle size 50 mm; 65 kg for 75 mm
Test duration per sample
2-5 days including drying, sieving and hydrometer sedimentation
Associated technical services
01
Full USCS Classification with Grain-Size Curve
Complete sieve and hydrometer analysis following ASTM D6913 and D7928, with Atterberg limits on the minus No. 40 fraction. The final report includes the cumulative grain-size curve, the USCS group symbol and group name, and the AASHTO classification with group index. We flag any soil that falls into the A-6 or A-7-6 groups because those indicate high plasticity and potential swelling under the Calgary climate.
02
AASHTO Subgrade Classification for Pavement Design
We determine the AASHTO group classification and group index specifically for pavement subgrade evaluation per ASTM D3282. This service includes the standard sieve analysis plus the liquid limit and plasticity index, and we calculate the group index using the standard equation GI = (F-35)(0.2+0.005(LL-40)) + 0.01(F-15)(PI-10). The result directly feeds into the AASHTO flexible pavement design method for Calgary roads and industrial yards.
Applicable standards
CFEM (Canadian Foundation Engineering Manual) (Standard Practice for Classification of Soils for Engineering Purposes – USCS), ASTM D3282-15 (Standard Practice for Classification of Soils and Soil-Aggregate Mixtures – AASHTO), CSA A23.2-2A (Standard Test Methods for Liquid Limit, Plastic Limit and Plasticity Index of Soils), ASTM D6913-17 (Particle-Size Distribution of Soils Using Sieve Analysis)
Frequently asked questions
What is the difference between USCS and AASHTO soil classification?
USCS (CFEM (Canadian Foundation Engineering Manual)) classifies soils based on grain-size distribution and plasticity into groups like GW, SP, CL, CH — it is the standard for geotechnical engineering worldwide. AASHTO (ASTM D3282) classifies soils into groups A-1 through A-7 with a group index that quantifies the subgrade quality for pavement design. Both systems use the same basic test data (sieve, Atterberg) but apply different boundary criteria. For Calgary projects we typically report both because the city's engineering standards reference AASHTO for roads and USCS for foundations.
How long does a full soil classification take in your Calgary lab?
A standard USCS classification including sieve analysis, hydrometer and Atterberg limits takes 3 to 5 working days from sample reception. The hydrometer sedimentation requires 24 hours of settling time for the 0.002 mm reading, and the oven-drying steps add another 12-24 hours. We can expedite to 2 days for urgent projects by running parallel sieving and Atterberg on separate splits, but the hydrometer timing cannot be compressed further.
What sample mass do you need for soil classification in Calgary?
The required mass depends on the maximum particle size in the sample. For a typical Calgary glacial till with cobbles up to 75 mm, we need 65 kg of dry material. For samples from the Bow River terrace sands (max particle 19 mm), 5 kg is sufficient. The ASTM D6917 standard specifies the minimum mass by sieve size — we always verify the sample meets the requirement before starting because undersized samples give biased gradations.
Does soil classification in Calgary need to account for frost heave potential?
Yes, absolutely. Calgary experiences up to 1.8 m of frost penetration in a typical winter. The USCS classification alone does not directly predict frost heave, but the fines content and the plasticity index from the classification are the primary inputs to the frost susceptibility criteria (FHWA and Canadian standards). Soils with more than 20% fines passing the No. 200 sieve and a PI below 10 are considered highly frost-susceptible — that combination is common in Calgary's glacial till, so we always flag it in the classification report.
