In the Haute-Yamaska region, many sites sit on loose sand and silt layers deposited by the Yamaska River. These deposits, at shallow depth in Granby, can lose strength fast under seismic loading. We run liquefaction potential analysis in Granby Quebec using field data from SPT and CPT, combined with lab grain-size curves. A standard penetration test alone is not enough; you need the fines content from a grain-size analysis to apply the NCEER/Youd-Idriss 2001 correction. Our lab in the Eastern Townships processes samples within 48 hours, so the factor of safety against liquefaction is not guesswork. We apply the Seed & Idriss simplified procedure, validated for the seismicity of southern Quebec. The output is a clear yes/no on liquefaction risk, plus settlement estimates if the soil will densify.
Liquefaction is not a yes/no from one SPT value — it's a chain of field data, lab fines content, and site-specific seismic demand from NBCC 2020.
Methodology applied in Granby Quebec
Risks and considerations in Granby Quebec
Granby sits on the edge of the Western Quebec Seismic Zone. While moderate, the NBCC 2020 design ground motion for a 2% in 50 years hazard is enough to trigger cyclic mobility in loose saturated sands. The Yamaska River floodplain deposits — mostly fine to medium sand with silt lenses — are the primary concern. If the factor of safety drops below 1.1, we calculate post-liquefaction volumetric strain using the Ishihara & Yoshimine 1992 chart, calibrated with our lab-measured relative density. The resulting settlement in Granby can reach 5-10 cm for a 3-meter liquefiable layer, enough to tilt shallow footings and break utility connections. We flag these zones clearly in the borehole log and the geotechnical report.
Our services
Our liquefaction assessment in Granby combines three deliverables into one report:
SPT-based liquefaction screening
We drill to 20-30 meters, record blow counts, and correct for overburden, hammer energy, and fines. Factor of safety per layer per NBCC 2020 seismic demand.
CPT continuous profiling and Ic classification
Cone penetration with pore pressure measurement. Robertson soil behavior type index (Ic) identifies liquefiable layers without disturbing the soil.
Lab grain-size and Atterberg limits correlation
Sieve and hydrometer analysis on split-spoon samples to determine percent finer than 0.075 mm. This fines content directly adjusts the CRR curve in the Youd-Idriss framework.
Frequently asked questions
How much does a liquefaction analysis cost in Granby?
The fee ranges from CA$3,240 to CA$6,350 depending on the number of boreholes or CPT soundings and the lab testing program. A typical project with two SPT boreholes, one CPT, and grain-size analysis on 8-10 samples falls near the midpoint. We provide a fixed-price quote after reviewing the site location and planned foundation type.
Which NBCC site class does Granby usually fall into?
Most sites near the Yamaska River floodplain are class D (stiff soil) or E (soft soil) due to the sand and silt deposits above the till. We measure Vs30 with MASW when the site class is borderline, because the amplification factor changes the design spectral acceleration significantly.
Can you run the analysis if we already have SPT logs from another contractor?
Yes, we can review existing borehole data and run the liquefaction triggering analysis as long as the logs include sample depths, blow counts, and soil descriptions. We do need a split-spoon sample for lab grain-size verification — fines content cannot be inferred from blow count alone.
What is the turnaround time for a full liquefaction report?
From field work completion to final report, we deliver within 5 business days. Lab grain-size tests take 2 days, and the triggering analysis and settlement calculations take one day. If you need a preliminary factor of safety sooner, we can send a draft within 48 hours of receiving the field data.