North Vancouver sites sitting on the Capilano Sediments demand a hard look at seismic performance. We see this daily in our lab—samples from Lower Lonsdale to Lynn Valley arrive with grain-size distributions that flag potential liquefaction risk under the NBCC 2020 seismic hazard values. The 49.3206°N location puts the city in a zone where crustal and subduction earthquakes both matter. Our team runs the cyclic triaxial tests and SPT-N correlations that tell the real story. Many boreholes in the District encounter loose silty sands between 3 and 12 meters depth, exactly the strata that need CPT testing to map continuous profiles without sample disturbance. We also cross-check with grain-size analysis on every split-spoon recovery because fines content shifts the liquefaction susceptibility threshold more than most engineers expect.
Fines content below 15% in a saturated sand at 6 meters depth is the point where we start seeing excess pore pressure ratios above 0.8 in our cyclic triaxial runs.
Process and scope
The rain-soaked glacial till and marine silts of the North Shore create a unique testing environment. Moisture conditions here—over 2,200 mm of annual precipitation on the slopes—keep the groundwater table unusually high, often within 2 meters of grade. That saturation is the trigger mechanism. Our laboratory procedures follow CSA A23.3 and ASTM D5311 for cyclic loading, but we adapt the confining pressure ranges to match the overburden stress typical of North Vancouver's dense urban lots. A sample from the Norgate area behaves differently than one from Deep Cove—the mineralogy changes, the angularity of particles shifts, and so does the pore pressure buildup curve. We measure it all. The post-liquefaction volumetric strain is what dictates foundation recovery, and that number comes directly from our triaxial cell data, not from a textbook correlation.
Applicable standards
NBCC 2020 – National Building Code of Canada, seismic provisions, CSA A23.3 – Design of concrete structures, seismic requirements, ASTM D5311 – Standard Test Method for Load Controlled Cyclic Triaxial Strength of Soil, ASTM D3999 – Standard Test Methods for the Determination of the Modulus and Damping Properties of Soils
Frequently asked questions
What soil types in North Vancouver are most susceptible to liquefaction?
The Capilano Sediments—loose to compact silty sands and sandy silts deposited in a marine deltaic environment—are the primary concern. We also identify liquefiable layers within the Vashon Drift where lenses of outwash sand are trapped between till units. Any saturated granular soil with less than 15% fines and an SPT N60 below 15 blows at depths shallower than 15 meters warrants laboratory cyclic testing.
How does NBCC 2020 change liquefaction requirements compared to NBCC 2015?
The 2020 edition updated the seismic hazard values for the North Shore, generally increasing the short-period spectral acceleration. It also clarified the requirement for site-specific response analysis on Site Class D and E profiles. For North Vancouver, this means more projects now trigger the liquefaction assessment requirement under Article 4.1.8.16, especially on sites with saturated sands within 10 meters of grade.
What is the cost range for a soil liquefaction analysis in North Vancouver?
A complete program—including cyclic triaxial testing on three specimens, index property testing, and the engineering report with factor of safety profiles—typically falls between CA$3,140 and CA$5,250. The range depends on whether undisturbed sampling is feasible or if we need to reconstitute specimens to target density, and on the number of layers requiring individual analysis.
How many cyclic triaxial specimens do you need for a reliable analysis?
We recommend a minimum of three specimens per critical layer, tested at different cyclic stress ratios to define the CSR-N curve. For a site with two distinct liquefiable strata, that means six specimens. This gives enough data points to fit a power-law curve and reduce the uncertainty in the factor of safety. For preliminary screening, a single specimen at the design CSR can provide a pass/fail indication.
Can you perform the analysis if only SPT data is available, without undisturbed samples?
Yes. When undisturbed sampling is not possible—common in the looser sands of North Vancouver—we use the SPT N60 values and fines content from the split-spoon recovery to select a target density. We then reconstitute specimens in the lab using moist tamping to that density and run the cyclic triaxial program. The results are correlated back to the field penetration resistance, and we provide a conservative factor of safety profile based on the Seed-Idriss simplified procedure updated with the NBCC 2020 PGA.
