Tunnel Business Magazine

FEB 2018

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Page 17 of 43

TUNNELINGONLINE.COM TBM: TUNNEL BUSINESS MAGAZINE // FEBRUARY 2018 F E A T U R E S T O RY 1 8 sible blocks, boulders or larger stones, a jaw crusher could be moved in from a parking position and activated in front of the suc- tion grid. This required a manual inter- vention and additional mechanical effort to change the operation mo diameters smaller than 8 m this becomes even more difficult. Although the Socatop project was to stay a one-of-a-kind solution for a rather long time, it showed conclusively that a com- plex combination of different technologies can make sense if the project circumstanc- es are right. In y 2013, Bouygues Civil Works Florida successfully completed the exca- vation of the P oad tunnel in Florida. The project comprises 1.2-km long twin-tube tunnels that cross the shipping channel and cruise ship terminal with their ends curving off to tie-in the existing road alignments on Watson and Dodge is- lands. The tunnels accommodate two traf- fic lanes, curbs, walkways, ventilation fans and additional safety features. Tunnelling f ort Tunnel in the Biscayne Bay was realized in porous and variable subsoil conditions of mainly sand and limestone and chloride ground- water. Due to high ground permeability in the porous formation and environmental concerns related to possible loss of slurry into the Biscayne Bay aquatic preserve, Ø12.87m) from Herrenknecht was selected to excavate and line the twin tub ould be adapted to deal with the variable ground conditions of locally high permeability where it was required to control the water and extract the rock at the tunnel face. The machine could be operated both in EPB mode with material discharge through the screw con- veyor onto a continuous conveyor muck handling system and in a water controlled process (WCP) mode with hydraulic muck- ing as the machine crossed beneath the channel and entered into the highly per- meable rocks. The WCP mode bypasses the discharge gate and the muck is processed directly from the screw conveyor through a crush- er and into a slurry pipeline to get pumped to a separation plant on surface. The system does not incorporate a crusher in the exca- vation chamber as done in a standard slur- ry machine. The cutterhead tool configura- tion is designed to limit the particles that can enter the excavation chamber to a size suitable for the installed screw conveyor. The WCP mode as designed f that excavated the P is a simplified system or preliminary step in the development of the Variable Den- sity where a rotary crusher-slurryfier box was designed in combination with the screw conveyor outlet. The rotary crusher- slurryfier box has to be moved into a park- ing position before the belt conveyor can be put in operation. Variable Density TBM, a new genera- tion of multi-mode soft ground TBM The demand of today's specific project conditions where frequent changes of soils, rocks and mixed face conditions of soils and rocks at the tunnel face are more and more common and this beneath the groundwater table had led to the develop- ment - also for small to medium sized - to change between operation modes, e.g. from a slurry supported face to an earth pressure supported face and this with full control of the face pressure also during the transition between modes. This new generation of multi-mode the Variable Density com- bines the individual advantages of each system in one machine. The development of the Variable D ocused on the goal to change between the closed operation modes (slurry and earth pressure face support) in the tunnel without any need of mechanical modification in the excavation chamber or behind the gantry in the tunnel area. The Variable Density can be operated as classic Slurry with an air bubble system to control the face pressure and in a full EPB mode. The change between the modes can be done gradually under permanent and full con- trol of the tunnel face pressure and with- out any need of chamber interventions. This machine can also be operated using Figure 2 - Functional Principles used for The "WCP – Mode" on the Port of Miami TBM. Figure 3 - Variable Density TBM, different tunneling modes for optimum adaptability in difficult soft ground.

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