In Brampton, the contrast between the shallow Halton Till plain and the deeper buried valleys of the Laurentian Channel creates a subsurface geometry that routinely complicates seismic site classification. A standard borehole log alone will not resolve the shear stiffness profile needed for NBCC 2015 Table 4.1.8.4.A compliance. The multichannel analysis of surface waves method delivers a continuous VS30 profile without coring through the stiff till-and-shale transition that wears down tooling on the east side of the Etobicoke Creek watershed. Our team runs 24-channel arrays with 4.5 Hz geophones, processing dispersion curves in the frequency–phase velocity domain to extract fundamental-mode Rayleigh wave data that feeds directly into the site-specific ground motion calculation. For sites near the Queen Street corridor where the water table sits within 2 m of grade, we pair the MASW line with a seismic refraction spread to constrain the P-wave velocity of the saturated overburden and isolate the water-table artifact from the true shear-wave depth model.
A 24-channel MASW array can resolve a 30 m shear-wave velocity profile in less than 40 minutes per spread, delivering NBCC site class directly from measured Rayleigh-wave dispersion.
Applicable standards
NBCC 2015 Part 4, Table 4.1.8.4.A — Site Classification for Seismic Site Response, ASTM D4428/D4428M-14 — Crosshole and Surface Wave Shear Wave Velocity Testing, NEHRP Recommended Provisions for Seismic Regulations, FEMA P-1050, CSA A23.3-14 — Design of Concrete Structures, Annex N (soil–structure interaction)
Common questions
What is the typical cost of a MASW survey for a single-building lot in Brampton?
How does MASW compare to downhole or crosshole shear-wave testing for NBCC classification?
MASW is a non-invasive surface method that measures the average shear-wave velocity over the entire array length, while downhole and crosshole tests measure velocity between fixed borehole intervals. In Brampton’s till-over-shale geology, MASW avoids the borehole-casing resonance and grout-coupling problems that can distort downhole records above 25 m depth. The trade-off is vertical resolution: a 3 m geophone spacing resolves layers no thinner than about 1.5 m, so thin high-velocity stringers may be averaged into the surrounding material. For sites requiring layer-specific velocity for soil–structure interaction models, a combined MASW-plus-downhole program provides both the spatial average and the discrete log.
Does the City of Brampton require a MASW survey for building permit applications?
The City of Brampton does not mandate a specific test method; it requires a signed geotechnical report that assigns an NBCC site class based on measured soil properties. When the site is underlain by more than 3 m of soft clay or loose fill — common in the older downtown blocks and along the Etobicoke Creek corridor — the geotechnical engineer of record typically recommends a MASW line because SPT-N correlations alone are unreliable for NBCC Table 4.1.8.4.A classification in these materials. The Building Division’s plan review staff may request the shear-wave velocity data directly if the proposed site class deviates from the default Class C assumption.
What is the minimum site access width needed to deploy a MASW array in Brampton?
A standard 24-channel array with 3 m geophone spacing requires a clear linear run of 69 m plus a few metres at each end for the source offset. On narrow Brampton infill lots — 12 to 15 m wide in the older A-section subdivisions — we reconfigure to a 2 m spacing with 48 channels, which maintains the 30 m depth penetration within a 94 m line but doubles the channel count. For lots under 50 m in any direction, a 2D array with orthogonal short lines or a passive-source microtremor array may be the only viable alternative, and we design the geometry case by case after a site walk.
