KVAERNER CEMENTATION Foundations has recently finished one of the first major soil nailing contracts in Eire.
Five hundred soil nails, typically 8m long, and 100 minipiles, typically 10m long, were installed to support temporarily the 8.5m deep basement excavation walls for a new terminal building at Dublin Airport.
Slopes were between 85degrees and vertical and faced with fabric and geogrid or reinforced gunite in more critical areas.
Ground conditions were stiff to hard boulder clay with cobbles and boulders overlying limestone at depth. Because there was a 3.5m height restriction over part of the site, Kvaerner, working for main contractor Michael McNamara, decided that soil nailing, combined with minipiling to underpin adjacent buildings, was the most cost-effective solution.
The firm says that as well as being fast and easy to install in the difficult ground, using soil nails also meant excavation props were not needed, making permanent slab and wall construction quicker, easier and cheaper.
And using minipiles was less risky than mass concrete underpinning, avoiding undermining of the existing bases. The small diameter grouted minipiles bonded the bases with the hard material at depth, reducing potential settlement.