TBM TUNNELING | TECHNICAL
“Each excavation stroke is followed by the ring
building sequence,” says Herrenknecht. It is stop-and-go, or ‘discontinuous’. A pause. The continuous tunneling approach overcomes the
pause to enable boring forward while simultaneously building rings. The system has been designed to do so by a different approach to the management of thrust cylinders where computerized controls permit the cylinders to operate individually while ensuring their combined effect has the right total pressure and direction of thrust, and so maintains the correct alignment of the excavation. The core idea is for the TBM operator to check
where the display panel is showing the current center of pressure, resulting from the combined effects of pressures in each thrust cylinder. On the panel, the operator next selects the desired center of thrust and the computerized system makes the adjustments across the cylinders. The ‘Center of Thrust (CoT)’ system moves operators
away from manual adjustments of rotary controls (potentiometers) on the control panel to adjust pressures in the thrust cylinders. Instead, in the new computerized control system, the adjustments are managed by algorithms to maintain the CoT spot selected by the operator. Removing the necessity of the pause offers
opportunity to save total time in each cycle of mechanized tunneling (total of excavation and ring building) and, consequently, in the larger construction operation. Soft ground tunnels could be built faster – and possibly the entire projects, too, depending on how well, after the civil engineering stage, the follow-on activities proceed, such as installation of railtracks/ roadways, M&E, signaling, lightning, ventilation, power, signage, and more. Herrenknecht said its continuous tunneling system is on two variable density slurry TBMs being used to build
some of the tunnels for Phase 1 of HS2 rail project, in the UK. Tunneling is well underway on the Chiltern Tunnel, in Lot C1, where Align JV (Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick) is using the two 10.26m-diameter machines to erect concrete rings of 2m length (7, incl key) and 400mm thickness. The TBMs ‘Florence’ and ‘Cecilia’ were launched in mid-2021. For its technological work, Herrenknecht previously
won accolades twice before at Bauma – for its E-Power Pipe system that supports power cable laying (2019), and for its Pipe Express system (2013) for laying pipelines.
SEGMENT PRODUCTION AUTOMATION As Herrenknecht notes, more producers are relying on automation tools that have proven their advantages and durability for concrete segment production. Advancing technology as well as there being too few skilled workers, the high cost of labor, the need for higher safety levels, and desire for faster, high quality production from lower cycle times are all among the drivers of the change. Efforts are focused on three areas of robotic support
– hydraulic opening/closing of molds, then cleaning and oiling them before pours, and then once concrete is cast and still wet to apply a rotating pipe-roller to achieve smooth and accurate surface finish. Each step saves time in delivering the quality sought.
For example, the hydraulically-operated mold can have all covers and side walls open in less than half a minute. The system doesn’t involve use of bolts (reducing maintenance needs, in that respect) but a hydraulic steering block to control pressures and obtain the required spatial dimensions and to tight tolerances. The rotating pipe roller delivers the required surface
density as it transports surplus material to the top of the curved casting, enabling voids to be filled, says Herrenknecht. It adds that the entire finishing process
Below left:
Example of a type of control panel for TBM operators to control thrust cylinders by settling a center of pressure/thrust. Cylinder pressures are then managed by computer
Below right: TBM employing continuous tunneling system on Chiltern Tunnel of HS2 project, in UK
Spring 2023 | 35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53
