HIGHWAY WIDENING - N18 BUNRATTY BYPASS. CO. CLARE, IRELAND

The N18 was constructed in 1990 over soft subsoils which were thought to be where the local river used to flow. The west bound section of the dual carriageway had settled quite substantially in five areas along the stretch adjacent to Bunratty Castle. Leca® LWA 10-20mm was used to replace the heavy road construction materials originally installed to the underside of sub-base.

The LECA® LWA was delivered by a 5000m3 capacity ship directly into the port of Foynes, not far from the site, and then transported over a period of two days in 60m3 high sided articulated tipper vehicles and loose tipped into a storage bund local to site.

Whilst the repairs were taking place, the westbound N18 traffic was temporarily moved onto the east bound carriageway reducing the N18 into a single carriageway. For this reason, time was limited and speed of installation was essential.

Once Clare County Council had excavated the first of the five areas that needed to be re-levelled, the LECA® Lightweight Expanded Clay Aggregate was transported from the storage bund and tipped directly into the void. The Leca® LWA was then compacted in one metre layers using a 360° excavator, the same equipment that was being used to distribute and level the Leca® LWA across the sub-formation. The use of LECA® LWA provided a simple lightweight solution. The design is expected to achieve a minimum of 20 year sustained design life.

The installation was very quick and simple and the contractor, Clare County Council Works Department, was happy with the speed in which they were able to carry out the works and re-open the busy N18 to traffic.

FACTS

Amount of material: 5000m3 of LECA LWA (10-20mm)

Interesting Fact: Leca® LWA 10-20mm was used to replace the heavy road construction materials originally installed to the underside of sub-base.

Delivery Method: 4-Wheel Articulated Tippers

Main Customer: Clare County Council

LECA® LWA within Highway Development

Construction of embankments over weak and compressible soil deposits, where the loading of the embankment causes soil consolidation and settlement, is common. Depending on the height of the embankment, the depth of the weak soil deposit and the consolidation properties of the soil strata, total settlements can be very deep and problematic in terms of road evenness, function and durability of the road construction. In the most difficult cases, various combinations of soil strengthening techniques are available, for example, preloading, vertical drainage and deep stabilisation with piles all of which are time consuming and costly to install.

By lightening the embankment in highway development with Leca® Lightweight Expanded Clay Aggregate, subsoil strengthening and lengthy settlement can be reduced or even avoided altogether. Using Leca® Lightweight Expanded Clay Aggregate on large scale cut and fill operations and construction on soft soils or bad ground can overcome stability problems, reducing the risk of landslide and deformation. Used in road embankments, Leca® LWA exerts much lower horizontal earth pressures compared with other backfill materials, helps improve stability and reduce the need for counterfill.