Geotechnical Excavation Monitoring in Ottawa: Protecting Shoring...

Excavating in Centretown with its urban fill is a different world from cutting into the sensitive Leda clay deposits south of Hunt Club. Ottawa’s geology shifts dramatically within a few kilometers, and a monitoring plan that works for a sandy till in Kanata can fail completely in the Champlain Sea silts of Vanier. Our team deploys instrument arrays that match the specific stratigraphy of each site, tracking lateral movement, groundwater fluctuation, and vibration transmission. Before installing the shoring, we often complement the subsurface profile with CPT soundings to identify thin drainage layers that trigger instability, and we verify the bedrock refusal depth with seismic refraction to ensure the monitoring anchors have competent grip. The goal is to detect deformation patterns before they become structural problems for the excavation or the adjacent heritage buildings.

A 4 mm/day creep in Leda clay at 11 m depth won't show on the surface—but it will fail a shoring wall within a week if unaddressed.

Scope of work

The core of our field kit for Ottawa projects centers on dual-axis in-place inclinometers with ±0.01 mm resolution, installed behind soldier pile and lagging walls or secant pile shoring. We pair them with automated total stations tracking prism targets fixed to neighboring facades, typically reading every 15 minutes during active excavation stages. In a recent downtown project near the Rideau Canal, the combination of vibrating wire piezometers and real-time inclinometer arrays allowed us to identify a 4 mm/day creep trend in a stiff clay layer at 11 m depth—movement that standard visual inspection would have missed. For deep cuts where blasting is required, we integrate triaxial geophones per O. Reg. 213/91 guidelines and cross-reference the data with grain-size analysis to correlate vibration attenuation with the fines content of the surrounding soil. Every sensor is calibrated to CSA A23.3 standards before deployment, and data streams into a cloud dashboard accessible to the structural engineer and the general contractor simultaneously.

Area-specific notes

The most common mistake Ottawa contractors make is assuming that a stiff, overconsolidated Leda clay will stand unsupported without generating pore pressure changes. They excavate, install the shoring, and skip the piezometers because the soil 'looks dry.' Six months later, a water main leak three blocks away migrates through a silty seam, saturates the clay interface, and the wall deflects 40 mm overnight. By the time the cracks appear in the adjacent building, the repair cost has already exceeded the monitoring budget by a factor of ten. Another frequent oversight is underestimating vibration damage to unreinforced masonry structures in Lowertown and Sandy Hill—the NBCC threshold of 5 mm/s PPV is not a suggestion. We also cross-check settlement readings with Atterberg limits testing when the excavation exposes clay layers with borderline plasticity indices, because a soil that shrinks aggressively during dewatering will produce settlement patterns that look alarming but are structurally manageable if predicted early.

Standards used

CSA A23.3-19 (Design of Concrete Structures – shoring references), NBCC 2020 Part 4 (Structural Design – excavation and shoring provisions), ASTM D6230-21 (Inclinometer monitoring procedures), O. Reg. 213/91 (Construction projects – vibration and blasting control), City of Ottawa By-law 2009-258 (Protection of adjacent properties during excavation)

Technical data

Parameter	Typical value
Inclinometer accuracy	±0.01 mm per reading
Total station angular precision	0.5” (Leica TS60)
Vibration threshold (heritage masonry)	5 mm/s PPV per NBCC
Piezometer range	0–350 kPa (vented transducer)
Data transmission interval	5–60 min adjustable
Typical monitoring duration	4–18 months per project

Common questions

What monitoring is legally required for a 7 m deep excavation in Ottawa clay?

Under NBCC 2020 Part 4 and the City of Ottawa's excavation by-law, any excavation deeper than 6 m—or shallower excavations that extend below the footing level of adjacent structures—requires a monitoring plan sealed by a Professional Engineer. At minimum, this includes settlement points on adjacent buildings, inclinometers in the shoring wall, and vibration monitoring if blasting or heavy compaction is planned. The specific sensor types, reading frequencies, and threshold values must be calibrated to the site's geotechnical report.

How quickly can you deploy instrumentation after receiving a contract?

For typical Ottawa projects, our field crew can mobilize within 5 business days of contract award. Inclinometer casings are installed during shoring construction; surface settlement points and prisms can be placed the same day the baseline survey is completed. Automated total stations and geophones require approximately 48 hours on site for calibration and networking before active monitoring begins. We maintain a local inventory of sensors to avoid supply-chain delays.

What is the typical cost range for excavation monitoring in Ottawa?

Monitoring budgets for a standard 6–12 month excavation in Ottawa generally range from CA$1.220 to CA$3.310 per month depending on the number of inclinometer strings, settlement points, and whether automated versus manual readings are specified. A full-service contract including installation, cloud data platform access, weekly engineering reports, and final close-out documentation typically falls within this range. Projects requiring vibration monitoring or real-time satellite-based settlement tracking are priced at the upper end.

Geotechnical Excavation Monitoring in Ottawa: Protecting Shoring and Adjacent Structures

Our service areas

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Excavations

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Scope of work

Area-specific notes

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Standards used

Technical data

Common questions

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