BTS, LINING – SLIPFORMING | TECHNICAL
Figure 2. Slipform Tunnelling machines - (left, top & bottom) Synchronous version for lining a tunnel whilst it is being excavated, and (right, top & bottom) the Non-Synchronous version for lining existing tunnels.
(Figure 2). To enable the material to be put into, and then “crushed” into place, “there has to be a resistance,” he said. As the Non-Synchronous system does not support new main tunnel excavation there remains a need for a reaction to oppose the force from the injectors. In this case, the solution is to have the injectors at an angle, “or vectored”. Additionally, it uses wheels, skids or both for additional braking force (as shutter friction will not be enough). They are mounted on hydraulic actuators, enabling the machine to be self-centring in combination with a position monitoring system and fuzzy logic control. The choice of wheel or skid depends upon the nature of the substrate.
NOVEL SUB-SYSTEMS At the heart of the Slipform TunnellingTM
machinery are two novel sub-systems: the injectors; and the shutter.
The injectors Injectors, located around the periphery, help to ensure efficient distribution of the lining material behind the shutter and also, by compressing the material, have reactionary forces that thrust forward the machine (Figure 3). They are, in effect, jacking off the lining – but the material is not precast but in the process of being compacted. The injectors act independently, placing and packing the material until the target pressure for each is achieved for quality, including around tunnel curves or in overbreak areas. Crucially, an integral cleaning system is fitted to flush and cool the injectors.
The shutter The shutter is a novel, passively articulated system formed from steel segmental rings and is expected to be only 3m-long, irrespective of tunnel diameter, Colin said. The steel rings of the shutter are tied together with high-tensile steel bars, tensioned using hollow cylinder jacks (connected in series, keeping the load in each bar the same, no matter its length). A compressible packer and gasket is incorporated at the joints, enabling passive articulation for the shutter to accommodate tight vertical and horizontal curves. Simplicity is key in the mechanised system and components can be replaced underground, if necessary, Colin said.
Forces, advancing, cleaning The forward push comes from the combined thrust of the actuator/injectors, which together overcome the total of: friction loss in the injectors; drag of TBM/shield and of the shutter; the nominal force needed to tow the trailing gear; and, also to support the face. There are a lot of actuators, Colin said: a typical machine design for Synchronous mode has 49 actuators. The typical stroke for the injector is about 300mm. The injections are relatively little and often. “A really important part of the design is the length of
the injector head” – sized to cover the material supply pipe and then beyond, leave the pipe open for flushing mode with the separate cleaning system working from behind, via the piston chamber. When the injector is withdrawn past the material supply pipe, and into the cleaned piston chamber, it is primed to stroke again,
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