A developer broke ground on a five-storey mixed-use building near the Speed River last spring. The geotechnical report flagged a stiff clay till at depth but the seismic site class was unresolved. We mobilized a 24-channel geophone spread across the site in under three hours. The MASW dispersion curve revealed a clear impedance contrast at 28 metres. That single line delivered a VS30 of 310 m/s and a firm Site Class C designation without a single borehole. For Guelph’s complex glacial stratigraphy, surface-wave methods often outperform traditional refraction in the upper 30 metres. We routinely pair MASW with SPT drilling when the till package is highly variable or with seismic refraction to constrain bedrock rippability where the dolostone is shallow near the Eramosa River escarpment.
A measured VS30 in Guelph’s glacial till can drop a Site Class from D to C and reduce base shear by 20 percent.
Scope of work in Guelph
Demonstration video
Local geotechnical conditions in Guelph
We have seen too many Guelph projects where the geotechnical report defaults to Site Class D “by assumption” because no VS data was collected. That conservative call triggers higher seismic design forces and can add 15–25 percent to the lateral system cost on a mid-rise structure. On one West End project the structural team pushed back and requested a MASW survey. The measured VS30 came back at 380 m/s—solid Site Class C. The foundation design stayed the same but the shear-wall reinforcement dropped noticeably. The NBCC 2020 allows site-specific modal analysis when VS profiles are available. Skipping the test means leaving that optimization on the table. In the south end near Clair Road, deep lacustrine silts sometimes produce VS30 values below 200 m/s. Knowing that early lets the designer select the right ductility class before the permit drawings are locked.
Our services
Our Guelph MASW program covers the full workflow from field acquisition to a NBCC-ready site-class letter. Each survey is designed around the specific subsurface conditions of the Royal City.
VS30 Site Classification Survey
One or more MASW lines placed to capture the representative ground conditions at the building footprint. Includes dispersion analysis, inversion to 1D VS profile, and a signed report with NBCC 2020 site class for the structural engineer of record. Typical turnaround is three business days.
Combined MASW + Seismic Refraction
A dual-method package for sites where bedrock depth and rippability are also design concerns. The MASW line delivers VS30 and site class; the refraction line maps the top-of-rock surface and provides P-wave velocity for excavation planning. Common on Guelph sites along the Eramosa River corridor.
Frequently asked questions
What does a MASW survey cost for a typical Guelph building site?
How long does the field work take and will it delay our building permit?
Field acquisition for a standard MASW spread takes one to two hours. We can often schedule within the same week of the request. The processed report with VS profile and NBCC site class is delivered in three business days, so it rarely sits on the critical path for a building permit submission.
Can MASW replace boreholes for site classification?
MASW provides the shear-wave velocity profile needed for NBCC seismic site class, which boreholes alone cannot measure directly. However, boreholes or test pits are still necessary for foundation design parameters like bearing capacity and settlement. We typically recommend combining MASW with at least one SPT borehole for a complete geotechnical picture.
What site class is most common in Guelph?
Most Guelph sites on glacial till fall into Site Class C (VS30 between 360 and 760 m/s) or Site Class D (180–360 m/s). Shallow dolostone bedrock in the northeast part of the city can push a site into Class B. Deep silt deposits in the south occasionally produce Class E. A measured VS30 is the only reliable way to know.