Self Drilling Anchors for Collapsed Viaduct
The main railway line between Dublin and Belfast suffered a major collapse on a viaduct that crosses the Broad Meadow Estuary at Malahide, just north of Dublin. Fortunately, the collapse happened just after a packed commuter train had crossed the old stone viaduct.
The solution was to core through the original stone piers and then to insert 5-6m long, 168mm diameter casings into the rock armor. The silts beneath were immediately grouted in order to ensure that the borehole was sealed down to competent ground below the base of the causeway.
Afterwards, a total of 192 up to 18m long R51N self drilling anchors were inserted through the permanent casing and drilled into dense gravel to underpin the original stone piers. At the two piers immediately adjacent to the collapse, 14 T76N self drilling anchors in lengths of 22m were installed vertically from track level to depths of 22m in order to attain working loads of up to 600KN.
All 11 piers and the abutments at both ends of the viaduct were underpinned with R51N self drilling anchors, using 100mm tungsten carbide drill bits. Simultaneous drilling and grouting was employed to ensure that the gravels in the proximity of the bore were fully permeated and any loose soils further consolidated.
The self drilling anchor was proved to be the ideal solution for working in loose granular soils below the pier footings.