Tunnel boring machine (TBM) manufacturer Robbins has said that the first of two crossover TBMs for the Mumbai Metro Line 3 has arrived on site.
The twin 6.65m TBMs will bore parallel 2.8km tunnels in mixed geology including basalt, shale, tuff, and breccia with possible water pressures up to 2bar.
Assembly and launch preparations for the first crossover machine is estimated to take about six weeks and will be ready to launch in August. The second will arrive on the site at the end of July ready for assembly.
Operation of these two machines will be carried out by Larsen & Toubro, part of the Larsen & Toubro - Shanghai Tunnel Engineering JV (L&T-STEC JV), while Robbins will provide key staff for the initial boring phase.
Mumbai Metro line 3 TBM
When completed the metro tunnels will run between the Cuffe Parade Station and Hutatma Chowk station, passing through the Vidhan Bhavan and Church Stations. Both crossover machines will be launched from the same 25m deep by 22m long shaft at the Cuffe Parade Station.
The TBMs will begin their excavation in hard rock mode, and the face of each will be equipped with six muck buckets and six large internal muck loading plates. This design, in combination with the screw conveyor located at the centerline of each machine, will allow for the option of fully emptying the cutterhead chamber, resulting in minimal wear, according to Robbins. Muck will be removed from the tunnels via muck cars.
Robbins projects manager India Jim Clark said: “Our target is to achieve an average of 250m of boring per month, and to complete the boring operations is 20 months, which includes the additional time required for the short start-up using umbilicals on the initial drives, dragging the machines and re-launching through three stations.”
Contractor Larsen & Toubro plan to work crews on double shifts in order to keep to this timeline.
The 33.5km long Line 3 on Mumbai Metro will have 26 underground stations and and a total of 17 TBMs will be used to excavate the new route.