In Ajax we often see pavement engineers wrestling with subgrade conditions that change dramatically between the lakeshore plain and the inland till deposits. The Duffins Creek watershed and proximity to Lake Ontario create moisture-sensitive silty sands that can lose bearing capacity fast if the pavement structure isn't tailored to the actual soil profile. A properly executed flexible pavement design here depends on more than traffic counts and asphalt thickness—it starts with a thorough site investigation and lab program that quantifies how the subgrade will behave under repeated loading through spring thaw and summer heat. We’ve supported road reconstruction projects along Bayly Street and new residential subdivisions near Audley Road where the difference between a 15-year and 25-year pavement life came down to the CBR and Proctor numbers we provided. Before committing to a structural number, local contractors will often pair our pavement analysis with test pits to visually confirm stratification at the formation level.
In Ajax, the difference between a pavement that lasts 12 years and one that lasts 25 is nearly always in the subgrade characterization—not in the asphalt.
Process and scope
Local ground factors
A 40,000 sq ft retail plaza off Harwood Avenue punched through the asphalt in three spots after just two winters. The original geotechnical report relied on boreholes taken in August when the water table was at its seasonal low. By January the silty sand subgrade had absorbed moisture from the adjacent stormwater pond, the CBR dropped below 2%, and the granular base pumped fines up through the asphalt cracks. The owner spent CA$180,000 on full-depth reconstruction plus underdrain installation—roughly triple what a proper flexible pavement design with saturated CBR testing and subsurface drainage analysis would have cost upfront. In Ajax’s climate, ignoring the worst-case moisture scenario is the single most expensive shortcut a developer can take on pavement works, and we see it repeated on sites from Pickering Beach Road to the 401 commercial corridor.
Reference standards
ASTM D1883-21 — CBR of Laboratory-Compacted Soils, AASHTO T 307-99 (2021) — Resilient Modulus of Subgrade Soils, ASTM D698-12(2021) — Standard Proctor Compaction, OPSS 501 — Ontario Compaction Standards for Granular B and Subgrade, Town of Ajax Engineering Standard Drawings — Pavement Structure Details
Other technical services
Laboratory CBR and Proctor Testing
Soaked and unsoaked CBR on remoulded samples compacted at standard Proctor effort, with moisture-density curves used to define the compaction specification for subgrade and granular layers.
Resilient Modulus (Mr) Determination
Cyclic triaxial testing per AASHTO T 307 for MEPDG-based pavement design, providing the stiffness input needed for arterial roads and high-traffic commercial lots in Ajax.
Frost Heave and Drainage Assessment
Evaluation of subgrade frost susceptibility based on grain-size distribution and Atterberg limits, combined with groundwater monitoring to set underdrain depths and granular base thickness.
Pavement Structural Section Design
Layer thickness and material specification—asphalt, granular A/B, subbase—calculated from design CBR and traffic loading, compliant with Town of Ajax standards and OPSS requirements.
Typical parameters
Questions and answers
What does flexible pavement design cost for a typical Ajax residential subdivision road?
For a local road segment in Ajax the geotechnical investigation and pavement design package typically runs between CA$2,490 and CA$6,150, depending on the number of boreholes or test pits, the lab testing scope (CBR, Proctor, grain-size), and whether resilient modulus or FWD correlation is required. This covers the soil sampling, soaked CBR testing, compaction curves, frost susceptibility evaluation, and the final pavement structure report with layer thicknesses suitable for Town of Ajax approval.
How do you determine the design CBR for Ajax’s silty sand subgrades?
We collect bulk samples from the formation level during test pitting or borehole drilling, then remould them in the lab at the target moisture and density from the Proctor curve. The samples are soaked for four days to simulate spring-thaw saturation before running the CBR penetration test. Where the subgrade varies across the site—common near the Duffins Creek corridor—we test multiple samples and recommend the design value based on the weakest representative zone, not the site average.
What pavement structure does the Town of Ajax typically require for local roads?
The Town’s standard drawings generally call for 40–50 mm of HL3 or HL4 surface course asphalt over 60–70 mm of HL8 binder course, placed on 150–200 mm of Granular A base and 300–450 mm of Granular B subbase, but the exact thicknesses depend on the subgrade CBR and the road classification. Our reports specify the structural number and layer thicknesses that meet both the Town’s minimums and the actual soil conditions we measure on site.
Can you design a flexible pavement section if the subgrade CBR is below 2%?
Yes, and it happens more often than you’d think in Ajax, especially where organic silts or saturated fine sands are encountered near drainage courses. When soaked CBR falls below 2% we evaluate subgrade stabilization with lime or cement, geogrid-reinforced granular layers, or a thicker subbase section to distribute loads. The final recommendation balances constructability, cost, and the required design life, and we include the stabilized mix design or reinforcement specification in the pavement report.