Unique Robbins TBM and Back-Up Will Make Short Work of Hong Kong Tunnels

The Po Shan Road project on Hong Kong Island is part of a much larger effort on the island to control groundwater accumulation during storms. The area, set on a very steep hill above the central business district, is prone to landslides during heavy rains.  Expensive homes and apartment buildings are located on the hills, so any slides would affect both residential and commercial property.

Many of the design elements on the machine for this project are due to site restrictions, including size of the work site. The entire site is just 25 m (82 ft) wide x 27 m (88 ft) long and the tunnel portal is 50 m (164 ft) from busy Po Shan Road. A high-end condominium building less than 50 m (164 ft) from the jobsite necessitated no-blast regulations and required a TBM-driven tunnel in order to minimize noise and vibration.

A specially designed back-up will aid the machine in boring the headings- a hydraulic power pack will be mounted on the rear section of the Robbins TBM, while the electrical transformers and electrical control cabinets will remain at the tunnel portal, connected to the TBM by umbilical cables containing power and electrical control cabling.  Muck is removed using a system of muck cars. The TBM conveyor rests on a stationary muck storage car that empties into a bottom conveyor. Muck is transferred from the conveyor to a traveling muck car pulled by a locomotive.

The tunnels are anticipated to be in mostly Grade I rock, predominantly granite and tuff with a UCS of 200 to 300 Mpa (29,000 to 43,500 psi).  A conventionally-mined access tunnel will serve as the launch site for the TBM, which will bore the 244 m (800 ft) long High Tunnel before being retracted and rotated to bore the 165 m (541 ft) long Low Tunnel. In order to make the TBM retractable, Robbins designed the cutterhead with bolt-on muck buckets and cutter housings. The reduced machine size will allow for TBM retrieval through the bored tunnel even after ring beams and shotcrete have been applied as temporary support.

Project specifications at Po Shan Road are part of a growing trend in the industry of tunneling in highly urbanized areas. "Restrictions on the use of explosives are becoming more common in high population density locations. Contractors therefore have to find more innovative ways to excavate hard rock in urban environments," said Joe Roby, Vice President of The Robbins Company.

Once boring at Po Shan is complete, several hundred sub-vertical holes will be drilled from inside the tunnel, up-hole. Water will be drained from the hillside into the drainage tunnels via these sub-vertical holes. A modified drill rig and hydraulic hammer rig will drill the holes and slotted drainpipes will be installed. The amount of drainage needed will be continuously monitored using standpipe piezometers fitted with automatic loggers. The meters will transfer data to engineering offices in real-time.  Water collected inside the tunnels will be channeled to a nearby public storm water drainage system.

Contact Information:
The Robbins Company
Brianna Home (Marketing Director)
5866 South 194th St.
Kent, Washington 98032 USA
Direct: +1 253 872 4484
eMail: homeb@robbinstbm.com
Web: http://www.robbinstbm.com

Desiree Willis (Technical Writer)
5866 South 194th St.
Kent, Washington 98032 USA
Direct: +1 253 872 4490
eMail: willisd@robbinstbm.com
Web: http://www.robbinstbm.com