Saint-Jerome’s expansion along the Rivière du Nord corridor brought heavy civil work onto terraces underlain by Champlain Sea deposits. Anyone who has excavated below three metres near Rue Saint-Georges knows the transition from dry granular overburden into grey silty clay can happen in the span of a single bucket. Our team approaches every deep excavation design here by mapping that contact first, because where La Mer clay appears the earth pressure diagram changes completely. In the lower Laurentians, a CPT test run to refusal gives a continuous pore-pressure and tip-resistance profile that picks up sensitive clay layers far better than SPT alone, and we integrate those readings directly into the shoring model.
When La Mer clay sensitivity exceeds 15, the difference between a stable cut and bottom heave is often a single day of rain.
Process and scope
Site-specific factors
Saint-Jerome sits near the northern limit of the Champlain Sea incursion, meaning the clay we encounter is often thinner and more desiccated than in the Montreal lowlands but still carries elevated salinity and a metastable structure. A week of July rain on a partly exposed cut can trigger small rotational slides that close the excavation overnight. The bigger threat is long-term creep in temporary berms left standing through freeze-thaw cycles, a problem we document regularly on multi-season projects near the old Cégep sector. We address this by specifying inclinometer casing behind the wall line as part of excavation monitoring, reading cumulative displacement weekly, and adjusting the strut preload before cracks appear at street level.
Reference standards
NBCC 2015 – National Building Code of Canada, Part 4 structural design, CSA A23.3-14 – Design of concrete structures for shoring elements, CFEM 4th ed. – Canadian Foundation Engineering Manual, earth pressure and deep excavation chapters, ASTM D2487 – Unified Soil Classification for Laurentian till and clay description
Other technical services
Shoring wall design and constructability review
Complete soldier pile and lagging or secant pile wall design with staged excavation profiles, strut and tie-back layout, and preloading schedules. We include a constructability review that accounts for winter shut-down periods and spring groundwater peaks typical of the Rivière du Nord basin.
Integrated monitoring plan for deep cuts
Instrumentation layout with inclinometers, piezometers, and optical survey points tied to the excavation sequence. We set alert thresholds based on the computed wall deflection envelope and track readings against the design assumptions throughout the project.
Typical parameters
Frequently asked questions
What is the typical cost range for geotechnical design of a deep excavation in Saint-Jerome?
For a project with a 5 to 10-metre cut, the design package including site investigation interpretation, shoring calculations, and construction drawings generally falls between CA$3,000 and CA$11,690. The final figure depends on the complexity of the ground profile, the number of support levels, and whether tie-back anchors or internal bracing are required.
How do you determine the earth pressure diagram for the sensitive clay found in Saint-Jerome?
We use the apparent pressure diagrams originally developed by Terzaghi and Peck, modified for stiff-fissured and sensitive clays. The envelope is calibrated against the undrained shear strength profile obtained from field vane tests and CPTu pore-pressure data. Where clay sensitivity exceeds 10, we increase the basal pressure component to account for possible strain softening during excavation.
Does the NBCC require a site-specific seismic analysis for deep excavations in Saint-Jerome?
Yes, under NBCC 2015 Part 4, a site-specific seismic evaluation is required when the excavation exceeds 6 metres in depth and is located within 100 metres of an existing building or a major lifeline. Saint-Jerome falls within a moderate seismic zone, and we include pseudo-static analysis of the shoring wall under the design earthquake ground motion specified for the area.
What groundwater control strategy works best in the fractured bedrock of the northern Saint-Jerome area?
The reference range for this service in Saint-Jerome is CA$3.000 - CA$11.690. The final price depends on the project scope and volume.
How do you manage bottom heave risk in excavations that bottom in La Mer clay?
We evaluate the factor of safety against basal heave using the bearing-capacity-based method from the CFEM. When the computed factor drops below 1.5, we extend the wall toe into the underlying till or rock, or specify a jet-grouted base plug installed before the final lift. Real-time inclinometer data at the wall toe provides early warning of heave movement during the critical excavation phase.