Laboratory CBR Testing for Pavement Design in Regina, SK

A contractor we work with regularly had a parking lot fail after two winters in east Regina—the asphalt cracked up in sheets. The culprit? A silty clay subgrade that looked fine during a dry August but turned to jelly after spring thaw. That project, off Prince of Wales Drive, taught us the same lesson every Regina pavement job reinforces: the CBR value of your subgrade isn't a formality. It’s the number that dictates whether your asphalt section survives the freeze-thaw cycles this city throws at it. At our lab, we run the Laboratory CBR test on remolded or undisturbed samples at the moisture condition that actually exists under your site—not a textbook assumption. We pair it with a grain size analysis when the fines content is suspect, because a CBR number without gradation context is half the story on Regina’s lacustrine silts.

A soaked CBR below 3% in Regina’s clay means your pavement structure isn’t a design choice—it’s a subgrade replacement decision.

Methodology and scope

West of Albert Street versus east of the Ring Road makes a difference in what you’ll get for a CBR value. The west side sits on slightly higher glacial till—denser, with more granular interbeds—and we routinely see soaked CBRs in the 6-8% range for native subgrade. Drive 10 minutes east toward the Pilot Butte Creek floodplain and the same depth of excavation hits soft, plastic clay where soaked CBR drops to 2-3%. That swing changes your pavement structural number by a factor of two. When we run the laboratory CBR test, we control compaction to Modified Proctor density per ASTM D1557 and then soak the specimen for 96 hours—four full days of saturation—because in Regina the water table rises fast after snowmelt. For projects needing a direct field benchmark, we often recommend cross-checking with an in-situ CBR test on the road alignment so the lab curve has a field-calibrated anchor point.

Local geotechnical context

Regina clay is lacustrine—deposited at the bottom of glacial Lake Regina roughly 11,000 years ago—and it has a shrink-swell potential that surprises engineers from out of province. A CBR test run at optimum moisture without soaking will grossly overpredict field performance. We’ve seen lab CBR values drop from 12% to under 3% after the 96-hour soak on a sample from the Harbour Landing area. That’s not an outlier; it’s the norm in post-glacial silts. If you build a commercial pad or a roadway section on a CBR assumed at 6% when the soaked reality is 2.5%, you’re looking at asphalt fatigue cracking within the first three freeze-thaw seasons. The laboratory CBR test, run properly, is cheap insurance against a pavement reconstruction that costs ten times the geotech budget. We always report both unsoaked and soaked values so the design engineer sees the full range of subgrade behavior.

Typical values

Parameter	Typical value
Standard referenced	ASTM D1883-21 / CSA A23.3
Sample preparation	Remolded at Modified Proctor (ASTM D1557) or undisturbed Shelby tube
Soaking period	96 hours minimum, water bath at 20°C
Surcharge weight applied	4.5 kg annular + slotted, per method
Penetration rate	1.27 mm/min ± 0.1
Readings recorded at	0.025 in (0.64 mm) increments to 0.300 in
Typical report values	CBR at 0.1 in and 0.2 in penetration, corrected if needed

Related services

Soaked CBR with Moisture-Density Curves

Full Modified Proctor compaction curve plus CBR specimens molded at optimum, 2% below, and 2% above—soaked and unsoaked pairs—to map the moisture sensitivity envelope for Regina’s silty subgrades.

Subgrade Soil Classification Package

Combined grain size, Atterberg limits, and laboratory CBR on the same sample. Delivers the USCS classification plus the soaked CBR needed for AASHTO empirical pavement design.

CBR Correlation with Field Testing

We run parallel lab CBR and in-situ DCP or field CBR tests so the design team has a site-specific correlation curve—critical on variable lacustrine deposits where one CBR number doesn’t represent the whole site.

Common questions

How long does a laboratory CBR test take in Regina?

From sample receipt to final report, plan on 7 to 10 calendar days. The compaction and molding takes one day, the 96-hour soak runs over four full days, and the penetration test plus data reduction takes another day. We can expedite to 5 days for a surcharge when the schedule is tight.

What does a laboratory CBR test cost for a Regina project?

A single-point soaked CBR with the companion Proctor curve typically runs between CA$180 and CA$330, depending on whether it’s a single specimen or a three-point moisture suite. Volume pricing applies when we’re processing multiple samples from the same subdivision or roadway alignment.

Do you need undisturbed or remolded samples for CBR testing?

Both work, but the answer depends on the project phase. For preliminary design, we test remolded samples compacted to the specified density. For forensic work on a failing pavement, undisturbed Shelby tube samples give us the in-situ density and structure—and we test those without remolding. We’ll guide you on which is right.

How does Regina’s clay affect CBR results compared to other Saskatchewan soils?

Regina’s glacial Lake Regina clays are more plastic and moisture-sensitive than the tills found in Saskatoon or the gravels near Moose Jaw. Soaked CBR values here routinely run 50-60% lower than unsoaked values, which is a bigger gap than in granular subgrades. That’s why the 96-hour soak isn’t optional for any Regina pavement design.