Medicine Hat sits on a complex alluvial plain carved by the South Saskatchewan River, where loose saturated sands and silty deposits can extend 15 meters or more below grade. With a population exceeding 63,000 and a growing footprint of mid-rise structures near the river valley, the seismic response of these soils is not a theoretical exercise. Our cyclic triaxial and CPT-based liquefaction analysis provides the numerical data required for geotechnical designs, quantifying cyclic stress ratios and post-liquefaction volumetric strain directly from undisturbed samples. In a region where the water table fluctuates seasonally between 2 and 5 meters depth, the margin between stable performance and seismic settlement is measured in small percentages of fines content. We run this testing under ASTM D5311 and correlate results with NBCC 2020 acceleration parameters to deliver factor of safety values for each critical layer.
Liquefaction in the river valley context is about settlement, not just bearing loss — a 15 mm differential settlement can shear utility connections long before structural collapse.
Our approach and scope
Local considerations
The hydraulic piston of a cyclic triaxial cell applies sinusoidal axial loads at frequencies between 0.1 and 2 Hz, while back-pressure saturation ensures B-values above 0.95 before shearing begins. In Medicine Hat, the biggest practical challenge is sample disturbance during extraction from saturated fine sands below the water table. Even minimal densification during sampling can artificially increase the cyclic resistance ratio by 20 percent or more, leading to unconservative designs. We address this by using thin-walled Shelby tubes with a stationary piston and immediate wax sealing on site. If the natural water content deviates more than 2 percent from the in-situ value, we reject the specimen and resample. This rigor matters because the difference between a safe design and a post-earthquake settlement that tilts a foundation wall often traces back to a single disturbed sample.
Reference standards
NBCC 2020 (Seismic Hazard and Site Classification), ASTM D5311 (Cyclic Triaxial for Liquefaction), CSA A23.3 (Concrete Structures — seismic design correlation), ASTM D1586 (SPT for field correlation), ASTM D5778 (CPT for liquefaction assessment)
Complementary services
Cyclic Triaxial Testing
Undisturbed samples tested under stress-controlled cyclic loading per ASTM D5311 to determine the number of cycles to liquefaction at various CSR levels.
CPT-Based Liquefaction Screening
Pore pressure dissipation tests and continuous tip resistance profiles used to calculate CRR via the Robertson (2009) correlation, corrected for fines content.
Post-Liquefaction Settlement Analysis
Volumetric strain integration using the Zhang et al. (2002) method, providing engineers with estimated settlement magnitudes for foundation design or ground improvement specifications.
Typical parameters
Common questions
What triggers a liquefaction study requirement in Medicine Hat?
Under NBCC 2020, sites classified as Site Class E or F, or those with saturated granular soils within 15 m of grade in a seismic zone, require a liquefaction assessment. The City of Medicine Hat typically requests it for any structure over three storeys or with a basement in the river valley corridor.
How long does a cyclic triaxial test program take?
From sampling to final report, expect 4 to 6 weeks. Consolidation and saturation alone can take 3 to 5 days per specimen in silty sands, and a standard program runs three specimens at different CSR levels to define the liquefaction resistance curve.
What does a soil liquefaction analysis cost for a typical Medicine Hat project?
A full liquefaction analysis including CPT profiling, sampling, and cyclic triaxial testing on three specimens ranges from CA$3,920 to CA$6,380 depending on depth and the number of critical layers identified during the field investigation.
Can you mitigate liquefaction risk without removing the soil?
Yes. Based on the factor of safety values we report, ground improvement methods like vibrocompaction or stone columns can densify the deposit in situ. We then verify the improvement with post-treatment CPT soundings to confirm that target CRR values are achieved.