MASW / VS30 Testing in Burlington: Subsurface Shear Wave Velocity

Burlington sits at roughly 74 meters above Lake Ontario, but the real story is underground. The city's position between the Niagara Escarpment and the lake basin creates a subsurface profile that varies dramatically within a single city block. Glacial till, dense silts, and the Queenston Shale bedrock all interact with seismic waves differently. A 2015 seismic hazard assessment by Natural Resources Canada placed Burlington within a moderate seismicity zone, which means site-specific ground motion analysis isn't just academic—it directly impacts structural design loads under NBCC 2020. The MASW method cuts through this complexity. Surface wave propagation analysis delivers a continuous VS30 profile without drilling, which proves invaluable when you're dealing with the unpredictable depth to bedrock found near the Escarpment's toe. We combine this with seismic refraction when the bedrock surface needs precise mapping for foundation decisions.

A VS30 value is not just a number for the geotechnical report—it's the single parameter that can shift your seismic design category by a full class.

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Methodology and scope

The overburden across Burlington is dominated by Halton Till—a dense, silty clay matrix with interspersed sand lenses that confuses traditional borehole-only investigations. VS30 values here typically range from 200 m/s in deeper soil deposits near the lake to over 600 m/s where shale is shallow along the Escarpment corridor. The MASW technique uses a 24-channel seismograph and 4.5 Hz geophones in a linear array. Active-source shots generate Rayleigh waves, and the dispersion curve extracted from the field data undergoes iterative inversion to produce a 1D shear wave velocity profile. Testing conforms to ASTM D6429-20 and the ESAC method for passive-source integration when greater depth penetration is needed. The resulting VS30 is calculated per IBC/ASCE 7-22 procedures, directly feeding into NBCC Site Class determination. A Class C profile (360–760 m/s) is common, but we've documented Class D conditions requiring de-amplification considerations. For deep infrastructure, the shear wave profile also feeds liquefaction assessment where saturated sand layers exist below the groundwater table.

MASW / VS30 Testing in Burlington: Subsurface Shear Wave Velocity — Technical reference — Burlington

Local considerations

A common mistake is assuming the NBCC default Site Class C for Burlington without testing. The Halton Till can look competent in a split-spoon sample, yet its shear wave velocity might fall into Class D or even E where deep lacustrine clays are present. That error means using a lower site coefficient in seismic calculations—underestimating lateral forces on the structure by 20% or more. On the other side, assuming Class E near the Escarpment when bedrock is actually shallow at 5 meters leads to over-engineering and wasted concrete. The Ontario Building Code references NBCC 2020 for seismic provisions, and the regulator expects a defensible VS30 value. A surface-based MASW survey provides that without the mobilization cost of a drill rig. It's also the only practical way to profile sites where access restrictions prevent heavy equipment from entering.

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Applicable standards

NBCC 2020 (National Building Code of Canada), ASTM D6429-20 (Standard Guide for Selecting Surface Geophysical Methods), ASCE/SEI 7-22 (Minimum Design Loads for Buildings and Other Structures)

Technical parameters

Parameter	Typical value
Test Standard	ASTM D6429-20
Geophone Frequency	4.5 Hz vertical component
Array Configuration	Linear, 24-channel
Maximum Investigation Depth	30–45 m (active + passive source)
Key Output Parameter	VS30 (m/s), NBCC Site Class A–E
Data Processing Method	MASW dispersion, ESAC passive
Applicable Code	NBCC 2020, ASCE 7-22

Frequently asked questions

What does a MASW survey in Burlington typically cost?

A standard active-source MASW survey for a single building site in Burlington ranges from CA$2,220 to CA$3,730. The price depends on the array length, whether passive-source integration (ESAC) is required for greater depth, and site accessibility. Multi-line surveys for larger developments are priced by linear meter of coverage.

How does MASW compare to a downhole seismic test for determining VS30?

MASW is non-invasive and measures the average shear wave velocity over the entire array length, which is often more representative than a single borehole measurement. A downhole test provides velocity at discrete intervals in one location but requires a cased borehole. In Burlington's till, where lateral variability in sand lenses is common, the spatial averaging of MASW often yields a more conservative and defensible VS30 for site classification.

Can MASW be performed on small or confined lots in Burlington?

Yes, but with array adaptation. The standard 46-meter linear spread requires open space. On smaller lots, we use a shortened array with higher-frequency geophones, which reduces maximum depth penetration to approximately 15–20 meters. For tight urban sites, a combined active/passive setup using a circular or L-shaped array can still produce valid dispersion curves without the full linear footprint.

What is the regulatory acceptance of MASW for NBCC 2020 site classification?

MASW is accepted by geotechnical reviewers across Ontario when performed and processed according to ASTM D6429-20 and the ESAC method. The Ontario Building Code references NBCC 2020 Table 4.1.8.4.A for site classification based on VS30. A report signed by a Professional Engineer with the raw dispersion curves, inversion parameters, and VS30 calculation is the standard deliverable for a building permit submission.

Location and service area

We serve projects across Burlington and its metropolitan area.

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