Eight variable density (VD) tunnel boring machines (TBM) were used on the project, four EPB TBMs and 16,000 tunnel segment rings installed. The 11 underground stations constructed also served as TBM launching and retrieval shafts.
Tunnelling in KL geology poses various challenges, particularly the tricky karstic limestone: tunnellers encountered complex geological interfaces between Kenny Hill, KL limestone and an abrasive granite region where frequent, almost daily stops were required to replace worn TBM cutting tools and to carry out preventative maintenance.
Other than the more complex geology, the Putrajaya Line tunnels also passed close to critical infrastructure, such as major railway lines, elevated transits, the SMART tunnel, and the Kajang Line tunnels. Despite the geological and other challenges, the Putrajaya Line is on target to open by January 2023.