Disassembly of the internal equipment of the 11m diameter Lovat EPBM working on Moscow metro is underway following completion of the 30 degree downward drive for an escalator access tunnel, and contractor Mosmetrostoy plans more such works.
The skin of the TBM has been left in place to support the tunnel lining during the disassembly, and the equipment is being withdrawn back up the bore to the surface.
Key design challenges for the large diameter TBM and the construction process had to be overcome for the full system to work successfully at that slope.
In addition, the 9.4m i.d. bore had to be done in EPB mode given the geology – dolomite, limestone, clay, marl, loam and loamy sand, and there being mixed ground conditions for much of the drive. The groundwater pressure met was up to 4.5 bar.
Lovat said that stabilising the centre of gravity was a key design challenge, which it solved with modifications to the cutterhead overcut diameter to provide the mounting of the main drive to be offset vertically higher. The change kept the shield from sinking at the invert by eliminating the gap between the skin and ground.
Materials handling on the downward slope also required a mine-type hoist system to supply 7.25 tonne segments to the backup. A bespoke segment car was lowered down the bore. The rings (6+1) are 10.6m o.d.
The TBM with a two-stage screw conveyor and high density pumping system to deal with spoil removal, and Lovat said this was an important technological advancement in its offering.
Manoeuvrability in excavating the 150m long escalator access tunnels came from two articulation joints and a cyclical copy cutter (T&TI, January 2008, p7).
Lovat supplied the design for the lining and segment forms as well as providing technical support, guidance systems, ground conditioning and grouting equipment.
