Calgary's glacial till and post-glacial alluvial deposits are overlain in many areas by engineered and uncontrolled fill from decades of urban development. The depth of these fills can reach several meters in districts like Bridgeland or the downtown core, where historical riverbank grading and industrial backfill created heterogeneous conditions. Before designing a foundation on fill, we run a campaign of boreholes and in-situ tests to profile the fill's composition, compaction level, and moisture content. In zones where fill is deep, results are combined with a MASW survey to obtain shear-wave velocity profiles and detect loose pockets that could cause differential settlement.
A single loose pocket of uncontrolled fill can produce 25 mm of differential settlement under a moderate column load if not identified early.
Methodology and scope
A typical project we worked on near the Bow River involved a four-story residential building over 4.5 meters of sandy silt fill placed during the 1970s. The fill had pockets of organic debris and old construction rubble, which made standard bearing capacity estimates unreliable. Our lab ran 12 dynamic cone penetration tests and 6 SPT borings on site, then correlated the blow counts to relative density using CSA A23.2-9A / CSA A23.2-9A / CSA A23.2-9A / CSA A23.2-9A / CSA A23.2-9A / ASTM D1586 procedures. For deeper fill zones, we also performed precarga-sobrecarga trials to gauge long-term compression behavior. The final foundation design used a mat slab on improved ground, with settlement predictions validated by our consolidation tests on undisturbed tube samples.
Technical reference image — Calgary
Local considerations
Calgary sits at an elevation of roughly 1,048 meters above sea level, with a semi-arid climate that subjects near-surface soils to seasonal moisture swings. In fill deposits, these cycles can cause volume changes of 3% to 8% in clayey fractions, leading to differential heave or settlement under foundations. The risk is magnified in older neighborhoods where fill was placed without compaction control, such as sections of Inglewood or Sunalta. Our team identifies these high-risk zones using a combination of georadar and test pits, then applies the NCEER-based liquefaction screening even for fills, since loose saturated sands can lose strength during a seismic event.
Continuous sampling and SPT at 0.75 m intervals through fill layers to identify weak zones, organic pockets, and density variations.
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Consolidation & Compression Testing
One-dimensional consolidation tests (CSA + CSA + CSA + CSA + ASTM D2435 (also CFEM Ch 2) (also CFEM Ch 2) (also CFEM Ch 2) (also CFEM Ch 2) (also CFEM Ch 2)) on undisturbed samples from fill to determine Cc, Cr, and preconsolidation stress.
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Plate Load Tests on Improved Fill
In-situ plate load tests (ASTM D1196) after dynamic compaction or preloading to verify modulus of subgrade reaction.
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Settlement Monitoring Program
Installation of settlement plates and inclinometers with bi-weekly readings during and after construction to track fill consolidation.
Applicable standards
CSA A23.2-9A / CSA A23.2-9A / CSA A23.2-9A / CSA A23.2-9A / CSA A23.2-9A / ASTM D1586 (Standard Test Method for SPT), CFEM (Description and Identification of Soids – Visual-Manual Procedure), NBCC 2020 (National Building Code of Canada – Part 4 Foundations), CSA A23.3-19 (Design of Concrete Structures – Settlement Criteria)
Frequently asked questions
How deep are typical fill deposits in Calgary?
Fill thickness in Calgary varies widely by district. In older industrial areas like Manchester or east of the downtown core, fills can reach 5 to 7 meters. Residential subdivisions on former agricultural land usually have 1 to 3 meters of engineered fill over glacial till.
What tests are most useful for foundation design on fill?
SPT with continuous sampling is the primary method to detect soft layers and organic material. For fills with high fines content, we also run Atterberg limits and one-dimensional consolidation tests. A georadar survey can quickly map the fill/till interface across the site.
What is the typical cost range for a foundations-on-fill study in Calgary?
A standard investigation covering boreholes, SPT, consolidation testing, and a geotechnical report falls between CA$1,070 and CA$3,140, depending on fill depth and the number of test points. Additional tests like plate load or MASW increase the total.
Can shallow foundations be used directly on fill?
Only if the fill is engineered, compacted to at least 95% of standard Proctor density, and verified by field density tests. For uncontrolled or heterogeneous fill, we recommend soil improvement (preloading or deep soil mixing) or deep foundations that bypass the fill layer entirely.
