A recent industrial access road near the River Barrow in Carlow started showing alligator cracking within eighteen months of opening. The pavement design had used generic CBR values without accounting for the silty alluvium beneath the topsoil. We were called in to forensic the failure, and the root cause was simple: the subgrade modulus used in the layer thickness calculations did not reflect what was actually underneath the formation level. In Carlow, where glacial tills and river gravels mix unpredictably with softer lacustrine clays, a desk-based assumption is a gamble. Our approach to flexible pavement design ties the structural analysis directly to site-specific geotechnical data, ensuring the asphalt, base, and sub-base layers work as a coherent system rather than a disconnected stack of materials. We combine laboratory characterisation with field assessment to give the pavement engineer a subgrade that behaves as predicted, not as hoped. A CBR road investigation provides the stiffness input, while grain size analysis confirms drainage characteristics of the unbound layers.
A pavement is only as good as the subgrade it sits on. In Carlow's mixed glacial deposits, that subgrade changes every hundred metres.
Methodology applied in Carlow
Demonstration video
Local geotechnical conditions in Carlow
The most common mistake we see on Carlow sites is treating the pavement design as a standalone exercise, disconnected from the earthworks specification. A contractor achieves a visually firm subgrade, the pavement designer assumes a CBR of 5%, and within two winters the surface is rutting because the actual soaked CBR was closer to 2%. The cost of reconstructing a failed pavement is three to five times the cost of a proper geotechnical investigation upfront. Another risk specific to Carlow is the presence of soft alluvial pockets along the Barrow and Burren tributaries: these lenses are often too small to appear on a regional geology map but large enough to cause differential settlement under a road alignment. We mitigate this by specifying a subgrade inspection protocol that triggers additional testing where the formation soil changes character. For industrial yards and logistics centres, where channelised heavy loading concentrates stress, we often recommend a Proctor-based compaction verification to ensure the upper subgrade achieves the stiffness assumed in the layer design.
Our services
Our flexible pavement design work in Carlow covers the full chain from subgrade investigation through to layer thickness optimisation. Each service is tailored to the specific traffic loading and ground conditions of the site.
Subgrade Assessment and CBR Programme
Field sampling, soaked CBR testing, and stiffness profiling to establish the design subgrade modulus for flexible pavement analysis. We map variability across the site so layer thicknesses reflect real ground conditions.
Pavement Layer Thickness Design
Mechanistic-empirical design of asphalt, base, and sub-base layers following NRA HD 26/06 for the specified traffic loading. We optimise layer thicknesses to balance construction cost against design life.
Drainage and Frost Protection Design
Assessment of granular layer permeability and frost susceptibility to ensure the pavement structure remains stable through Carlow's wet winters. We specify filter criteria to prevent fines migration between layers.
Questions and answers
How much does a flexible pavement design investigation cost in Carlow?
For a typical road or yard project in Carlow, the geotechnical investigation and pavement design package ranges from €1,670 to €4,840, depending on the number of CBR samples, the linear metres to be assessed, and whether laboratory testing includes advanced parameters like resilient modulus.
How is the subgrade CBR value determined for a Carlow pavement design?
We extract undisturbed or remoulded samples from the formation level, soak them for 96 hours to simulate worst-case moisture conditions, and test penetration resistance following IS EN 13286-47. The soaked CBR value is the direct input into the pavement thickness design charts.
What traffic loading can a flexible pavement in Carlow be designed for?
We design flexible pavements for traffic loads from 1 million standard axles for residential access roads up to 80+ msa for heavy industrial yards and logistics hubs. The design life typically spans 20 to 40 years depending on the client's maintenance strategy and the criticality of the asset.