Laboratory CBR Test for Pavement Design in Tralee

Designing a pavement in Tralee means accounting for two fundamentally different ground conditions that exist just a few kilometres apart. The compact glacial tills underlying the town centre and Ballyseedy tend to deliver reliable bearing capacity once properly compacted, while the alluvial silts along the River Lee floodplain near Blennerville exhibit far lower stiffness and demand careful CBR verification. This contrast becomes critical when specifying sub-base thickness for access roads servicing new residential developments around the Tralee-Fenit greenway corridor. A laboratory CBR test run under controlled moisture and density conditions provides the soaked strength value that feeds directly into pavement design catalogues, removing the guesswork that leads to premature rutting. We complement this with grain size analysis to confirm fines content and Atterberg limits to flag plasticity risks before compaction begins.

A soaked CBR of 3% versus 8% can double the required pavement thickness — that difference alone justifies a €200 laboratory test on every subgrade material in Tralee.

Our approach and scope

On sites around Tralee, we frequently see imported granular fill that looks competent in the stockpile but degrades significantly when saturated. The laboratory CBR test captures this behaviour explicitly: a specimen compacted at optimum moisture content is submerged for 96 hours under a surcharge weight simulating overlying pavement layers, then penetrated with a 49.6 mm diameter piston at 1.27 mm/min. The force required to achieve 2.5 mm and 5.0 mm penetration is ratioed against a standard crushed stone reference, yielding the CBR percentage. We run the test in triplicate when variability is suspected, particularly on the glaciofluvial deposits common along the Dingle Peninsula approach roads. For larger infrastructure projects, the soaked CBR value is correlated with plate load test results to validate in-situ stiffness assumptions and refine the modulus of subgrade reaction used in rigid pavement design.

Local considerations

Tralee sits at just 5 metres above sea level in the town centre, with groundwater frequently encountered within 1.5 metres of the surface in the Ballymullen and Cahermoneen areas. Subgrades that test at CBR 8–12% during a dry summer can drop below 3% after a wet Kerry winter, triggering differential settlement and alligator cracking across the pavement surface. The laboratory CBR test explicitly models this worst-case scenario through the 96-hour soak, but a common oversight is failing to match the compaction energy to the actual site specification — using standard Proctor when modified Proctor is required underestimates density and inflates the CBR value. On brownfield sites near the former Denny bacon factory, we have measured CBR values as low as 1.5% on saturated made ground, requiring full subgrade replacement or stabilisation with stone columns before pavement construction can proceed.

Technical data

Parameter	Typical value
Standard followed	I.S. EN 13286-47:2021
Mould diameter	152 mm (CBR mould)
Compactive effort	Standard or Modified Proctor (I.S. EN 13286-2)
Soaking period	96 hours submerged, surcharge applied
Penetration rate	1.27 mm/min
Typical specimen mass	4.5–5.0 kg per mould
Testing temperature	20 ± 2 °C (water bath)
Report turnaround	5 working days standard

Related services

Soaked CBR determination

Four-day submerged test at specified compactive effort, with swell measurement and penetration curve analysis.

Modified Proctor compaction

Determines maximum dry density and optimum moisture content per I.S. EN 13286-2, the prerequisite for CBR specimen preparation.

In-situ density correlation

We pair laboratory CBR with field sand cone density testing to verify that site compaction achieves the target percentage of maximum dry density.

Pavement thickness design input

Interpretative report translating CBR values into equivalent subgrade strength categories for TII pavement design catalogues.

Relevant standards

I.S. EN 13286-47:2021 – Unbound and hydraulically bound mixtures – Test method for the determination of California bearing ratio, I.S. EN 13286-2:2010 – Test methods for the determination of dry density and water content (Proctor), TII Publication CC-SPW-01200 – Specification for Road Works Series 600 – Earthworks, NRA HD 26/06 – Pavement and Foundation Design (legacy, still referenced regionally)

Frequently asked questions

What does a laboratory CBR test cost in Tralee?

A standard soaked CBR test on a single sample ranges from €100 to €220, depending on whether compaction curve determination is included. Testing three points for a full moisture-density relationship increases the total. We provide a fixed quote before work begins, with no hidden charges for swell measurement or penetration curve reporting.

How long does it take to get CBR results for a pavement design submission?

The soaking period alone requires 96 hours. Including sample preparation, compaction, soaking, penetration testing, and reporting, the standard turnaround is 5 working days. We can expedite to 4 days when project schedules demand it, though the soak duration cannot be shortened without compromising the test's validity under I.S. EN 13286-47.

Can you test CBR on site in Tralee or is it laboratory only?

The formal soaked CBR test is exclusively a laboratory procedure because it requires controlled compaction into a rigid mould and a 96-hour water bath. For rapid field assessment, we offer the Dynamic Cone Penetrometer as a complementary in-situ index, which we then correlate against laboratory CBR values from the same formation. This is particularly useful on linear projects like the Tralee Bypass where conditions change frequently.