MASW & VS30 Testing in St. Albert, AB

St. Albert sits at roughly 689 m elevation, straddling the transition between the glacial till plains and the deeply incised Sturgeon River valley. This creates wildly different seismic responses across short distances. We have measured VS30 values dipping below 180 m/s in saturated river clays near downtown, while the stiff till uplands in neighbourhoods like Erin Ridge routinely register above 400 m/s. Getting those site-specific shear wave numbers right is the difference between a realistic seismic design and an expensive overbuild. Our field crew runs the full 24-channel active-source MASW survey, processing the dispersion curves back in our lab to deliver a clear, defensible VS30 profile ready for your geotechnical report.

NBCC 2020 Table 4.1.8.4.B prompts a Class E investigation when shear wave velocity at 30 m stays below 180 m/s — a common measurement in St. Albert's valley floor clays.

Our service areas

Our approach and scope

The soil contrast between the Braeside flats and the Lacombe Park bench is exactly why a single default site class won't cut it in St. Albert. On the floodplain, you hit soft lacustrine silts and organic clay layers extending 15 m deep before competent till. The low shear wave velocity in those materials demands a rigorous Class E or F evaluation under NBCC 2020. Up on the bench, the dense lodgement till provides much better numbers, but the occasional buried pre-glacial channel can introduce an invisible low-velocity zone. Our array configuration lets us map that contrast cleanly, and we pair the results with CPT probing when the client needs to tie the velocity profile directly to tip resistance and sleeve friction for a refined liquefaction screening.

MASW & VS30 Testing in St. Albert, AB — Technical reference — St Albert Alberta

Site-specific factors

NBCC 2020 Division B, Part 4 requires a site-specific shear wave velocity measurement when the ground conditions suggest a possible Class E or F seismic site. Ignoring the soft clays and organic silts mapped extensively along the Sturgeon River and Big Lake margins by the Geological Survey of Canada puts the structural design at risk of underestimating the spectral acceleration. The engineering risk isn't just a higher lateral load: it's the potential for resonance in the 0.5–1.5 Hz band that can amplify ground motion, a concern Seed and Idriss documented extensively in soft soil amplification. A field campaign with MASW costs far less than the structural upgrades required if the design starts from the wrong site class.

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Email: info@geotechnicalengineering.vip

Reference standards

NBCC 2020 (National Building Code of Canada, Division B), CSA A23.3-14 (Design of Concrete Structures, seismic provisions), ASTM D7400-19 (Standard Test Method for Downhole Seismic Testing, referenced for methodology principles)

Typical values

Parameter	Typical value
Survey method	Active MASW, 24-channel, 4.5 Hz geophones
Max investigation depth	Typically 30 m, extendable with passive-source combination
Parameter delivered	VS30, shear modulus profile, site class per NBCC
Array length	46 m or 69 m standard, adapted to site access
Source type	Sledgehammer (accelerated weight drop for deeper targets)
Data processing	Dispersion curve inversion, 1D shear wave velocity model
Seismic site classification	Class A through F per NBCC 2020 Table 4.1.8.4

Common questions

What does a MASW survey cost in St. Albert?

A standard active-source MASW line to 30 m depth, processed to a VS30 profile and site class letter, runs between CA$2,410 and CA$4,920 depending on line length and access. A combined active-passive survey for deeper targets (50–60 m) falls at the upper end.

How long does it take to get the VS30 report?

Fieldwork is typically one day for a single array. Back in the lab, we run the dispersion analysis and inversion within 4 business days, delivering a signed PDF report with the velocity profile and the NBCC site class determination.

Why can't you just use the default site class from the geological map?

The surficial geology maps show broad units, but the shear wave velocity in St. Albert's valley clays can vary from 150 to 250 m/s within 100 m laterally. NBCC 2020 requires site-specific measurement when the default class would be E or F, precisely because that variation has real structural cost implications.

Does the MASW survey disturb the site?

No drilling or excavation. We lay out a geophone spread on the ground surface and strike a plate with a sledgehammer. The survey leaves no disturbance and we can work on graded pads, grassed areas, or asphalt with good coupling.

Location and service area

We serve projects in St Albert Alberta and surrounding areas. More info.

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