Ajax sits on a shallow overburden layer above the Ordovician bedrock, just 90 meters above Lake Ontario. This changes everything for seismic site classification. The 2020 NBCC now requires site-specific shear wave velocity data for most mid-rise buildings, and the generic Class C assumption often fails here due to rapid impedance contrasts within the first 30 meters. We run MASW surveys with 24-channel arrays to capture the fundamental-mode dispersion curve cleanly, even when cultural noise from the 401 corridor or the GO Transit line interferes. Our processing workflow picks the correct dispersion branch for Ajax's typical stratigraphy: stiff clay till over weathered shale. The result is an unambiguous Vs30 value for your structural design.
A Vs30 value derived from an incomplete borehole is a liability. Full-wavefield methods give you the complete 30-meter profile, no gaps.
Process and scope
Local ground factors
The most common mistake we see in Ajax is skipping the geophysical survey entirely and classifying the site as Class C based on a handful of SPT N-values. That shortcut backfires when the site is actually Class D or E. The difference is a 20–40% increase in seismic base shear. Post-tender reclassification forces structural redesign, and the schedule impact can exceed the entire testing budget tenfold. Another risk is running MASW on a Friday afternoon with heavy truck traffic 50 meters away. The passive-source energy from the road masks the fundamental mode, and the dispersion image becomes uninterpretable. We schedule surveys during low-noise windows and use active-source stacking to suppress transients. Every Ajax report includes the raw dispersion image so the reviewing engineer can verify the mode identification.
Reference standards
NBCC 2020 – National Building Code of Canada (seismic provisions, Part 4), ASTM D4428/D4428M-19 – Standard Test Methods for Crosshole Seismic Testing (MASW shares equipment and processing standards), ASCE/SEI 7-22 – Minimum Design Loads (site classification tables for U.S. reference), CSA A23.3-19 – Design of Concrete Structures (references NBCC site class)
Other technical services
Vs30 Site Classification Survey
Full MASW acquisition with two orthogonal spreads. We deliver Vs30, site class per NBCC 2020 and ASCE 7, and a signed engineering report ready for building permit submission. Includes time-averaged Vs profiles and spectral acceleration parameters.
Combined MASW + Refraction Package
We shoot both MASW and seismic refraction on the same geophone spread. You get Vs30 from surface waves plus a P-wave bedrock depth map from refraction. Ideal for sites with suspected shallow bedrock or variable overburden thickness.
Typical parameters
Questions and answers
How much does a MASW survey cost in Ajax?
For a standard Vs30 site classification survey in Ajax, the cost ranges from CA$2,390 to CA$3,710, depending on the number of spreads, site access conditions, and whether you need a combined refraction survey. We provide a fixed-price quote after reviewing your site plan.
How long does it take to get the report?
Fieldwork takes half a day for a single-spread survey. The processing and interpretation require 3–5 business days. Rush delivery is available if you need the Vs30 data for a permit deadline.
Can MASW work on asphalt or concrete surfaces?
Yes, we can couple geophones to pavement using base plates anchored with wax or quick-set plaster. The surface wave energy propagates through the pavement into the underlying soil. We have run many surveys in Ajax parking lots and industrial yards without issues.
What depth does the MASW method reach?
With a 69-meter spread and a 10-kg sledge source, we reliably resolve the Vs profile to 30–35 meters in the glacial soils typical of Ajax. If you need deeper data, we can extend the array or use a weight-drop source, though 30 meters covers the NBCC Vs30 requirement.