Preparations are being made on a tight hillside site in Hong Kong to receive a 3.5m Ø Robbins TBM designed to run in short mode for driving two stretches of drainage tunnel as part of a slope stabilisation scheme.
The work site in Northern Hong Kong Island’s Wan Chai area is only 25m-27m wide and the tunnel portal is less than 50m from expensive apartments, restricting the options for back-up on the project, which has been mandated as a shield drive due to restrictions on blasting. It is an example of the more innovative ways being developed for non-blasting tunnel solutions in urban environments, notes Robbins VP Joe Roby.
For the Po Shan Road project, Robbins has developed a mucking out arrangement involving spoil delivery by conveyor to a storage car behind the TBM, with its own bottom conveyor. From there, spoil will be transferred to a shuttling muck car that is pulled by a loco. Other aspects of the back-up arrangement for the TBM include a hydraulic power pack mounted at the rear of the machine while electrical transformers and cabinets will remain at the portal, connected by umbilical cables.
In August, the main beam TBM is due to be launched to drive a 50m long access tunnel that will lead to a pair of bores set out in a two-pronged arrangement – the 244m High Tunnel and the 165m Lower Tunnel. The bores will be driven through Grade I granite and tuff of UCS 200MPa-300MPa. Housing 17” front-loading cutters, the new type of cutterhead does not rely on welding and consists of a 250mm thick front plate with a cone and flange behind.
Also mounted on the cutterhead will be muck buckets and cutter housings that are removable. The arrangement will enable the size of the TBM to be reduced for retrieval to the access adit following the 225m-radius High Tunnel drive and then rotated for relaunch.
Lining will be bolts, mesh, shotcrete, ring beams and a final 200mm thick concrete shell.
Robbins sees potential to use the back-up elsewhere, and is exploring the possibility for another project. The company also sees possibilities to using the removable elements-concept to reduce TBM size during projects elsewhere. It added that for the Po Shan Road project, the non-welded cutterhead was tailored to make assembly easier in China.
Contractor on the Po Shan Road project is China State/China Railway JV, and from the two main tunnels it will bore a series of drainage holes to be fitted with slotted pipes for regulated groundwater drainage to the public storm water network.
The landslide prevention project is part of a wider scheme in Hong Kong to control groundwater levels during storms.
Robbins assembles its TBM for short mode drives on Hong Kong drainage tunnels Robbins TBM assembly Robbins assembles its TBM for short mode drives on Hong Kong drainage tunnels Robbins TBM HK
