The cyclic triaxial apparatus is the beating heart of any liquefaction assessment worth its data. In our Moncton setup, we run stress-controlled cyclic loading on undisturbed Shelby tube samples recovered from the silty sands of the Petitcodiac River basin. The machine applies sinusoidal axial loads at frequencies calibrated to the 2,475-year seismic event defined in NBCC 2020 — for Moncton, that means PGA values around 0.12g on firm ground, amplified by the soft estuarine deposits that blanket much of the city. We prepare specimens at in-situ density, saturate them under backpressure until Skempton’s B-parameter exceeds 0.95, and then count the cycles to 5% double-amplitude axial strain. That number — whether it is 8 cycles or 28 — determines if the layer triggers liquefaction at design Mw 7.0. The same sample set often feeds a companion grain-size analysis to check fines content against the Bray & Sancio criteria, because a soil with 35% passing #200 behaves entirely differently than a clean sand with 2% fines.
Liquefaction in Moncton is not a theoretical exercise — loose silty sands at 4 meters depth with groundwater at 1.5 meters produce factors of safety below 0.8 more often than most designers expect.
Technical details of the service in Moncton
Demonstration video
Critical ground factors in Moncton
The Petitcodiac River causeway — opened in 1968 and now partially replaced — altered sedimentation patterns for five decades, depositing a thick sequence of loose, compressible silts upstream of the gate. That legacy sediment sits directly beneath parts of downtown Moncton and the expanding Dieppe commercial corridor. Combine those young deposits with a water table that hovers within 2 meters of grade from March to November, and you have all three ingredients for liquefaction: loose granular soil, full saturation, and seismic shaking. The 2020 NBCC assigns Moncton a moderate hazard, but site amplification through soft clay and silt layers can push surface acceleration well above the rock reference. Factor in a fines content that varies from 5% to 40% across the same site, and a single CPT sounding may miss a critical lens. That is why our protocol runs at least three investigation points per building footprint when the desktop geological review flags the Tantramar marsh or river-terrace deposits. Ignoring lateral spreading potential along the riverbanks — where gentle 0.5% slopes can displace laterally by over 300 mm during a design event — is a liability no EOR should carry.
Our services
Liquefaction analysis in Moncton requires a layered approach — screening-level assessment first, then advanced laboratory or in-situ testing where the simplified procedure returns borderline factors of safety. Our lab runs both paths concurrently to keep the project schedule moving.
SPT-based Liquefaction Screening & Settlement Estimate
Borehole logging with SPT N60 measurements at 1.5-meter intervals through the critical upper 15 meters. We apply the Idriss-Boulanger triggering correlation with Moncton-specific magnitude scaling and overburden correction. Output includes factor of safety per layer, liquefaction potential index (LPI), and post-triggering settlement using Ishihara-Yoshimine volumetric strain curves. Typical delivery: 5 business days from last field log.
Cyclic Triaxial Liquefaction Testing (ASTM D5311)
Undisturbed Shelby tube samples tested under stress-controlled cyclic loading at CSR levels bracketing the design earthquake demand. We report cycles to 5% DA strain, excess pore pressure ratio (ru), and post-cyclic shear strength. Each specimen is reconstituted to field density and saturated to B ≥ 0.95. The curve of CSR versus cycles to liquefaction anchors the site-specific resistance, eliminating the uncertainty of SPT or CPT correlations in Moncton's variable estuarine silts.
Common questions
Does Moncton really have a liquefaction hazard worth investigating?
It does. The Petitcodiac River basin contains Holocene alluvial and estuarine sands that are loose, saturated, and within the upper 10 meters. NBCC 2020 assigns a moderate seismic hazard, but site amplification through soft soils can double the surface acceleration. We have measured N60 values below 10 in boreholes across Dieppe and central Moncton — those layers will trigger under PGA above 0.10g.
What is the difference between SPT-based and CPT-based liquefaction screening?
SPT screening uses blow counts corrected for energy, overburden, and fines content to estimate cyclic resistance ratio. It works with the drilling rigs already mobilised for logging. CPT screening provides continuous resistance profiles without soil disturbance, giving higher resolution on thin seams. In Moncton's interbedded silts and sands we often run both: SPT for sampling and index testing, CPT to fill the gaps between boreholes.
How much does a liquefaction analysis cost for a Moncton building site?
A complete package — including SPT-based screening, LPI calculation, settlement estimate, and the engineering report — typically ranges from CA$3,180 to CA$6,190, depending on the number of boreholes and whether cyclic triaxial testing is required. Boreholes with SPT at standard intervals run approximately CA$95 to CA$140 per linear meter in the Moncton area.
How long does the laboratory testing take?
Cyclic triaxial testing under ASTM D5311 takes 7 to 10 business days from specimen preparation to final data reduction. SPT-based screening and settlement estimates can be delivered within 5 business days of receiving the field logs. We provide preliminary results by email as soon as the last cycle count is confirmed.
What do you need from the geotechnical driller to start the analysis?
Borehole logs with SPT N-values at 1.5 m intervals, groundwater level recorded at time of drilling and after 24-hour stabilisation, soil descriptions including fines content estimate, and undisturbed Shelby tube samples from any sand layers where N60 < 15. The tubes must be wax-sealed, labelled with depth and borehole ID, and kept upright during transport to Moncton — vibration during shipping can densify loose samples and overestimate cyclic resistance.