Laboratory CBR Testing for Pavement & Earthworks in Newbridge

A contractor rang us last Tuesday afternoon about a stretch of new access road off the R445 near the Curragh for a logistics shed. The resident engineer wasn't satisfied with the field density readings on the capping layer and wanted a soaked CBR value by Thursday morning. We see this pattern every season in Newbridge—gravelly glacial tills that compact well on paper but soften noticeably after 96 hours of soaking in the mould. Our laboratory on the Naas road handles the full cycle: sample receipt, moisture conditioning to I.S. EN 13286-47, surcharge ring assembly, and plunger penetration at 1.27 mm/min. When the CBR at 2.5 mm penetration falls below 15% on a capping, it usually means the grading envelope is too wide and fines are migrating. We cross-check with a grain-size analysis from the same sample to confirm the particle distribution and pinpoint the fraction causing the swell.

A CBR test without the full moisture-density curve is just a number—we need the compaction curve to know if the soil was placed at 95% of MDD before the plunger ever touches it.

How we work

The alluvial gravels near the Liffey floodplain east of Newbridge town behave entirely different to the lodgement tills up by the train station. The till gives CBR values between 8% and 25% unsoaked, dropping to 4%–12% after four days submerged, while the river terrace gravels often hold above 30% soaked if the cobble fraction is clean. That contrast matters when you're designing pavement foundations for a distribution centre versus a housing estate link road. One job last autumn near the Whitewater extension had us running soaked CBR on six bulk samples from the same borrow pit because the fines content varied from 12% to 34% across the face. That kind of scatter tells the designer whether to spec a stabilised sub-base or rely on mechanical interlock. Where the soaked CBR stays stubbornly below 5%, we recommend the design team consider stone-columns as a ground improvement option before placing the pavement layers, particularly on soft silty clays that show low penetration resistance.

Local considerations

Newbridge grew fast during the 1990s and early 2000s, with housing estates spreading onto agricultural land that had never seen heavy pavement loading before. Some of those access roads were built on silty clays with CBR values under 3%, and within five years the surface course was cracking at the edges and rutting in the wheel paths. The underlying problem was simple: the design assumed a soaked CBR of 5% based on a desk study, but the actual subgrade was much weaker, and the capping thickness wasn't adjusted. We now routinely see engineers requesting laboratory CBR before tender, not because the standard changed, but because the cost of pavement failure is too visible around Kildare. Tight marl deposits and laminated silts near the canal are particularly tricky—they look firm in the cut face but lose strength rapidly when saturated. A soaked CBR test on a remoulded specimen at the compaction target reveals the weakness before the asphalt goes down.

Applicable standards

I.S. EN 13286-47:2021 – Unbound and hydraulically bound mixtures – Test method for the determination of California bearing ratio, TII Specification for Road Works Series 600 – Earthworks (Transport Infrastructure Ireland), I.S. EN 13286-2 – Determination of dry density and water content (Proctor relation), BS 1377-4:1990 – Soils for civil engineering purposes – Compaction-related tests (referenced where not superseded)

Technical data

Parameter	Typical value
Standard applied	I.S. EN 13286-47:2021 (soaked & unsoaked)
Mould diameter	152 mm (CBR mould with collar)
Compactive effort	2.5 kg rammer, 450 mm drop, 5 layers × 62 blows (Proctor)
Surcharge mass	Annular weights equivalent to 50–120 mm pavement
Penetration rate	1.27 mm/min ± 0.1 mm/min
Soaking period	96 hours submerged, swell monitored daily
Reporting	CBR at 2.5 mm and 5.0 mm penetration, corrected for concavity
Sample mass required	Minimum 25 kg per specimen (retained on 20 mm sieve)

Common questions

How much does a laboratory CBR test cost in Newbridge?

A standard soaked CBR test on a single specimen runs between €100 and €190, depending on whether you need the full Proctor compaction curve alongside it. If we're running multiple points from the same bulk sample, the per-point cost drops. We quote per job, not per specimen, so you know the total before we start.

How long does a soaked CBR test take from sample drop-off?

Minimum five working days. Day one we dry back or add water to condition the sample, then compact and assemble the mould with surcharge rings. The specimen soaks for 96 hours with daily swell readings. Penetration and data reduction happen on day five. Unsoaked CBR on granular material can be reported in 24 hours.

Do you test samples from outside Newbridge or only local sites?

We receive samples from across Kildare, west Wicklow, and south Dublin. As long as the material arrives in sealed bags with chain-of-custody paperwork, we treat it the same as a sample from a Newbridge site. We will arrange courier collection if you need it.

What sample mass do you need for a CBR test?

At least 25 kg per specimen if the material is retained on the 20 mm sieve, or 15 kg for finer soils. The standard mould is 152 mm diameter, so we need enough to compact five layers at the required compactive effort plus extra for moisture content determination. If you are unsure, call us before dispatching and we will advise based on the material description.

Which CBR value is used in the pavement design: 2.5 mm or 5.0 mm?

I.S. EN 13286-47 specifies that the test report must include both values, corrected for any concavity in the curve. The pavement designer typically uses the higher of the two as the design CBR, provided the correction is applied correctly. If the 5.0 mm value exceeds the 2.5 mm value, we flag it in the report and may recommend re-compaction or a check on the density achieved.

Laboratory CBR Testing for Pavement & Earthworks in Newbridge

Our service areas

In-Situ Testing

Foundations

Slopes & Walls

How we work

Local considerations

Need a geotechnical assessment?

Applicable standards

Technical data

Common questions

Location and service area