Seismic Amplification Analysis in Drummondville

Drummondville grew fast along the Saint-François River during the industrial boom, and much of its soil profile reflects that glacial and fluvial history. The city sits on a mix of Champlain Sea clay, sand terraces, and till from the last ice retreat. That layered stratigraphy creates sharp impedance contrasts, which means seismic waves can amplify unpredictably as they travel through soft clay into denser sand or till. We have seen projects where ignoring this effect led to unexpectedly high accelerations at the surface. Before any structural design, we run a full seismic amplification analysis in Drummondville to quantify that risk and match it to NBCC 2020 site class criteria.

A 2-second shift in fundamental period can double the base shear on a mid-rise building in Drummondville clay.

Our service areas

Ground improvement

Geotechnical drainage design ›Prefabricated vertical drain (PVD) design ›Preloading with surcharge design ›Geogrid specification ›Geomembrane specification ›

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Slopes & Walls

Soil erosion analysis ›Slope stability analysis ›Debris flow analysis ›Geocell design ›Slope stabilization design ›

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Laboratory

Proctor test (Standard or Modified) ›Soil mechanics study ›Laboratory permeability test (falling/constant head) ›

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Methodology and scope

The NBCC 2020 assigns site classes based on average shear-wave velocity in the top 30 meters, and for Drummondville that typically falls into class C or D depending on clay thickness. We follow ASTM D4428 for MASW surveys to measure Vs30 directly, then combine those profiles with a MASW Vs30 study for deeper resolution. When soft clay exceeds 10 m we also run a microtremor HVSR to identify the fundamental frequency of the soil column. The whole process ties back to CSA A23.3 for the structural interface.

MASW array: 24-channel geophone spread, 2 m spacing
HVSR recording: minimum 30 minutes per station
Site class verification per NBCC Table 4.1.8.4.A
Nonlinear site response using DEEPSOIL or equivalent

We calibrate each model against existing borehole logs from the area.

Technical reference — Drummondville

Local considerations

A common mistake we catch on Drummondville sites is assuming a single soil type controls the whole response. Contractors often pick a generic site class from old maps without considering the impedance jump between the soft marine clay and the underlying till. That jump can amplify spectral accelerations by 40% or more at mid-rise building periods. If the structural engineer uses a uniform spectrum without site-specific amplification, the design may be unconservative by a wide margin. We have documented cases where this oversight required post-construction ground improvement to meet the NBCC drift limits.

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Explanatory video

Applicable standards

NBCC 2020 (National Building Code of Canada), CSA A23.3:19 (Design of Concrete Structures), ASTM D4428/D4428M-18 (MASW testing), NEHRP Recommended Seismic Provisions (FEMA P-1050)

Technical parameters

Parameter	Typical value
Shear-wave velocity (Vs30)	180–360 m/s typical (Site Class D–C)
Fundamental site frequency (f0)	0.8–2.5 Hz depending on clay thickness
Peak ground acceleration (PGA)	0.18–0.32 g per NBCC 2020
Amplification factor (Fa)	1.0–1.6 per NBCC site coefficient
Soil column depth modeled	30–50 m to bedrock
Nonlinear degradation (G/Gmax)	Darendeli 2001 curves applied

Frequently asked questions

What is the difference between seismic amplification analysis and a standard geotechnical investigation?

A standard investigation focuses on bearing capacity, settlement, and soil classification. Seismic amplification analysis specifically evaluates how the soil column modifies earthquake ground motions — it measures shear-wave velocity, fundamental frequency, and nonlinear soil behavior. It is required for NBCC site class assignment and for performance-based design of structures in Drummondville.

How much does a seismic amplification analysis cost in Drummondville?

For a typical commercial or residential project, the range is CA$1.400 to CA$2.820. This includes field MASW survey, HVSR recording if needed, lab correlation, and the full numerical site response report. The final cost depends on the number of test stations and the complexity of the soil profile.

Is seismic amplification analysis mandatory for all buildings in Drummondville?

Not for every building, but the NBCC 2020 requires it for post-disaster buildings and for structures in Site Class F. For ordinary buildings in Site Class D or C, a simplified site coefficient can be used, but we recommend the full analysis for any building over 4 stories or with irregular geometry. The insurance and safety benefits usually outweigh the cost.

How long does the field work and reporting take?

Fieldwork typically takes one day for a standard MASW survey with 6 to 10 stations. Data processing and report writing take another 5 to 7 business days. For projects requiring nonlinear site response analysis, add 3 to 4 days for the numerical modeling. We can expedite if the schedule is tight.

Location and service area

We serve projects across Drummondville.

Location and service area