Tunnel Business Magazine

FEB 2018

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Page 20 of 43

TUNNELINGONLINE.COM F E A T U R E S T O RY 2 1 TBM: TUNNEL BUSINESS MAGAZINE // FEBRUARY 2018 the attached slurry circuit to the Slurry Treatment Plant at surface. In slurry and high density mode the muck transfer along the screw conveyor is a combination of a mechanical and hydraulic transportation. In case of required simplified crusher maintenance the screw conveyor flat gate has to be closed and the slurryfier box can be accessed in free air. Variable Density TBM (Ø7.41m) for Hong Kong's Shatin to Central Link Contract 1128 The Shatin to Central Link (SCL) in Hong Kong is a strategic rail line that stretches from Tai Wai to Admiralty. It connects several existing rail lines and passes through multiple districts in Hong Kong. When finished it will serve areas in East Kowloon that currently do not have an ervice and will also strengthen the linkage betwe erritories and Hong Kong Island. The Dragages-Bouygues JV has won the contract to construct 2x2 tunnels that will form part of a 6-km long extension of the Shatin to Central Link. Tunneling works comprise two eastern tunnels (up-track and down-track) of each approximately 590 m in length that will run from the south ventilation building and the new Exhibition station on the Shatin to Central Link and two western tunnels (up-track and down-track) of each approximately 510 m that will be excavated between Fen- wick Pier emergency egress point and the existing Admiralty station. The up-track tunnels are deeper tunnels; the down-track tunnels are shallow tunnels. All tunnels are to be constructed in complex geologi- cal conditions that comprise very variable geology that is mainly composed of com- pletely decomposed granite (CDG) with the presence of boulders, corestones and tran- sition zones in mixed face conditions and sections of alluvium and marine deposits. These heterogeneous conditions along the specific sections demand the use of two different typ liquid supported tunnel face and the city's first Variable D Three sections, the two western tunnels and the up-track tunnel of the eastern sec- tion are planned to be excavated using a e start- ed opera ch 2016. The Variable D Ø7.41m), was launched in August 2016 to excavate the down-track shallow tunnel section of the eastern tunnels. This section is characterized by large portions within fill material that is frequently composed of rock fill blocks in the previous temporary seawall zone. The Variable D ontinuously adapt to the face density to deal with the demand of the predicted heterogeneous and shallow ground conditions. The can be operated both in a slurry and high density mode. The latter mode is used to cope with the very variable geology as- sociated with shallow cover of locally less than 1 diameter where possible risks such as blow outs and settlements might have been an issue in slurry mo can be operated also with the Slurry Treatment Plant on surface is accordingly designe Two Variable Density TBMs (Ø7.05m) for Forrestfield Airport Link in Perth, Australia Salini Impr W Pty Ltd. JV was contracted to construct the twin tube rail tunnels for the Forrestfield Air- port Link project in Perth, Australia. The Forrestfield Airport Link is a new rail line including two twin tube tunnels that have a bored tunnel length of about 7.14 km. This new rail line will connect Bayswater Junction with Forrestfield. A major section of the alignment crosses beneath the Perth airport precinct. This includes sensitive area beneath the airport runways, taxi- ways and buildings. The expected subsurface conditions along the bored tunnel alignment are char- acterized to be variable, sand, clayey sand and cemented layers with varying degrees of strength and cementation. The major- ity of the tunneling ground is expected to be composed of mixed face conditions be- neath the groundwater table. With focus on the predicted vary- ing geological units and their varying strength the application of two Variable D onsidere with a diameter of 7.05 m will be oper- ated along the entire tunnel alignment in closed pressurized mode to guarantee ground stability during excavation. The machines will be launched at Forrestfield dive portal, extending westward and end- ing at the Bayswater dive portal. The Variable D or the For- restfield Airport project are configured to operate in closed EPB and in slurry mode with a filled excavation chamber and a con- trolled support of the tunnel face pressure. Both in EPB and slurry mode the muck is extracted out of the pressurized excava- tion chamber via the screw conveyor and further processed with liquid mucking re- spectively hydraulic material transport via a closed, pressurized slurry circuit accord- ing to the slurry mode or operation with a slurry treatment plant at surface. To support the hydraulic muck transport, the muck is transferred at the end of the screw conveyor into a slurryfier box to liquefy the excavated material. A roller crusher is installed in the slurryfier box that process- es the material to a size suitable for hydrau- lic mucking via slurry circuit. The two Variable Density or Perth started tunneling in July and Sep- tember 2017. In the past a large number of tunneling projects were successfully completed in sensitive areas. The machines applied to date show the highest technical and qual- ity standards of mechanized tunneling technology mastering project challenges and individual tasks in the interest of cus- tomers, clients and the environment. Conclusion With the first introduction of multi- mo chnology in 1980s and the further development in multi-mode technology with the possibility to change between various operation modes in the tunnel, e.g. from open to closed EPB and slurry mode and also to change between the two soft ground modes, the founda- tion was laid for the new generation of multi-mode soft ground the Vari- able D e machines can smoothly and with continuous setting of the face pressure change between the op- eration modes from EPB to slurry, even in small and mid-r A major technological advantage of these machine types is that the set face pressure can be kept during the transi- tion of operation mode and the need for working chamber interventions is avoided. The number of applications of this new generation of multi-mode soft gr vantage of having a safe solution at hand even for potential high risk areas to support a set- tlement controlled operation with less impact to man and envir of today's tunneling projects feature complex heterogeneous geology and en- vironment with low overburden or the demand of crossing beneath important and sensitive structures. With the state- of-the-art Variable D ch- nology these projects can be safely and reliably implemented. Karin Bäppler is Head of Geotechnics and Consulting-Traffic Tunnelling, Herrenknecht AG; Frédéric Battistoni is Division Manager-Traffic Tunnelling, Herrenknecht AG; and Werner Burger is Manager of the Design Division-Traffic Tunnelling, Herrenknecht AG.

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