 Extensive remedial works were undertaken between 1999 & 2001 to strengthen the dam wall . This work involved removing the top 3 @.@ 8 m ( 12 ft ) of the existing dam wall and drilling / blasting through the dam wall plus up to a further 70 m ( 230 ft ) into the bedrock below . The top section of the wall was then rebuilt using reinforced concrete . Finally , permanent , re @-@ stressable ground anchors were then installed through the formed and drilled holes from the crest to be stressed and grouted into the foundation rock . At time of completion , these were the largest capacity and longest permanent ground anchors ever installed in the world . 
 Extensive remedial works <a href='uninflect' title='1'><mark>were</mark></a> undertaken between 1999 & 2001 to strengthen the dam wall . This work involved removing the top 3 @.@ 8 m ( 12 ft ) of the existing dam wall and drilling / blasting through the dam wall plus up to a further 70 m ( 230 ft ) into the bedrock below . The top section of the wall was then rebuilt using reinforced concrete . Finally , permanent , re @-@ stressable ground anchors <a href='uninflect' title='2'><mark>were</mark></a> then installed through the formed and drilled holes from the crest to be stressed and grouted into the foundation rock . At time of completion , these <a href='uninflect' title='3'><mark>were</mark></a> the largest capacity and longest permanent ground anchors ever installed in the world . 
Extensive remedial works was undertaken between 1999 & 2001 to strengthen the dam wall . This wrk involved removing the top 3 @.@ 8 m ( 12 ft ) of da existing dam wall and drilling / blastin through tdadam wall plus up to a further 70 m ( 230 ft ) into thdaedrock below . The top section of the wall was then rebuilt using reinforced concrete . Finally , permanent , re @-@ stressable ground anchors was then installed thru thedarmed and drilled holes from the dast to be stressed and grouted into the fdadation rock . At time of completion , these was the ladast capacity and longest permanent ground anchors ever installed in the world .