In October 2008, McDonnell Piling & Foundations Limited carried out the installation and testing of ground anchors for R.T.E. at Mullaghanish, County Cork. The overall project consisted of the construction of a 220m high telecommunication mast, together with the construction of a series of reinforced concrete stay blocks and connectors. The stay bocks were retained using Dywidag ground anchors.
Killarney Telecom Limited were appointed to construct the stay blocks with Turmbau Steffens & Nölle of Berlin, Germany, appointed as project engineers in charge of the design and construction of the mast.
As part of the tendering process, McDonnell Piling & Foundations Limited (McD) outlined a scope of works for the installation and testing of all ground anchors. Due to the location of the site, on top of Mullaghanish mountain, several technical and logistical issues had to be addressed;
The proposed location for the stay blocks and anchors consisted of soft peat over sandstone rock. McDonnell Piling & Foundations Limited carried out a series of dynamic probes at each stay block location, so as to determine the exact depth of the overlying peat and to plot an accurate profile of the underlying rock.
Following detailed examination of the working loads, ground conditions and restricted site access, McDonnell Piling & Foundations Limited proposed a series of 24 number Dywidag double corrosion protected 63.5mm GEWI 555/700 monobar anchors. Each anchor was designed for a maximum safe working load of 817Kn with a total length of 9m. Eight number stay blocks were to be retained by 3 number anchors at each location. All anchors were to be installed at a rake, ranging in angle from 40° to 55.5° to the horizontal.
McD proposed that all anchors were to be installed using a Boart DB100 piling rig. Due to the narrow access roads, the layer of soft peat at stay block locations and requirement for drilling to be carried out at a rake, the Boart DB100 proved to be the ideal machine. It is a 12 tonne track mounted unit with an overall width of 2480mm and length of 8300mm.
Installation of Anchors
At each stay block location the peat layer was excavated to expose the underlying sandstone rock. Using steel mats to spread the rig load, McD tracked the Boart DB100 to each stay block location prior to drilling commencing.
Boart DB100 rig drilling 150mm D.T.H.Hammer system.
A 150mm diameter borehole was drilled to the designed depth at each anchor location. On completion the anchors were installed and grouted from toe level using tremie pipes.
Testing of Anchors
All 24 number working anchors were subjected to acceptance testing and were tested to 1.5 times working load, 1225.5Kn. One sacrificial anchor was installed and tested to 80% of the ultimate capacity of the anchor, 1700Kn.
Anchor Testing at Mullaghanish, Co. Cork.
All anchors were successfully tested, with all final results within the design parameters.
McDonnell Piling & Foundations Limited completed all anchor works on site in late October 2008, the overall project was completed in January 2009.