Tunnelling works for Dubai's 15km-long Route 2020 rail network are 50% complete, the head of the emirate's Roads and Transport Authority (RTA) confirmed.
Construction completion rates for the network's stations range from 4% to 42%.
HE Mattar Al Tayer, director-general and board chairman at RTA, said tunnelling works for the project span 3.2km, with depths varying from 12m to 36m.
The Al Wugeisha Expo 2020 tunnel boring machine (TBM) commenced tunnel drilling works at Al Furjan, passed through Discovery Gardens, and reached the underground station near Jumeirah Golf Estates (JGE) last February.
Tunnelling works will continue up to the Dubai Investment Park (DIP), with all tunnel-related activities scheduled for completion this December.
Architectural, construction, and electro-mechanical designs are currently being developed for the Expo 2020 station, the network's elevated and underground stations, and the Nakheel Harbour and Tower station.
The underground station at JGE is 42% complete, while the underground station at DIP is 8% complete.
Al Furjan's and Discovery Gardens' elevated stations are respectively 14% and 12% complete, while the Expo and Nakheel stations are 7% and 3% complete.
Construction works for the deep foundations and pillars at Discovery Gardens have been completed, and the manufacturing of metal structures for the neighbourhood's elevated station is 35% complete.
Deep foundations work for the Nakheel station are 50% complete, while the footbridge linking the station to the Park-n-Ride Terminal has been removed to begin the new station's construction works.
The casting of reinforced concrete for the foundations of Expo station's main building has commenced, and works to cast concrete pillars have passed the 70% mark.
Construction of pillars and walls of the Expo station's western and eastern gates are respectively 90% and 40% complete.
Up to 60 viaduct segments have been installed in various parts of the project, and all viaduct construction is due to complete in November 2018.
The project's Al Wugeisha TBM can crush stones and penetrate through sandy layers any soil components it encounters during the drilling process.
The machine features metal gear supported by an automated tail, and a cutting wheel with a cavity that varies in shape according to the type of drilling and soil layers.
RTA's Al Tayer said the project is proceeding as per approved timelines, with the first metro carriages for the development due to arrive this July.
Rail works for Route 2020 are expected to complete in July 2019, with RTA set to commence test runs in February 2020, Dubai Media Office reported.