Underground Singapore 2011 The machine that NFM delivered for this job is in charge of boring a total of 12 km in several sections. It goes across a widely varied geology, from very hard rock (granitoid rock with porphyry inclusions, up to 180 MPa), folded and alternating shale layers, fragmented and weathered rock, clayey marls and completely weathered granite. The choice was made to use a Dual Mode machine that can operate in either EPB or open mode, with a belt conveyor muck transport system. In order to handle the geology changes along the drive, it was decided to design and manufacture several cutter heads, each one of them specifically adapted to the given corresponding geological context. Three cutter heads have therefore been provided. The first one follows a pure hard rock design, but with openings in the face and drag bits for soft ground, that allows it to be used in EPB mode. The second one is of the soft ground type, with arms and plates, bearing drag bits for both directions of rotation, and on which disc cutters or tilting scrapers can be mounted indifferently. The third cutter head is a genuine hard rock design, with a fully closed face, perfectly adapted to operate in open mode through the granitoid rock section. The main characteristics of the Barcelona machine are as follows: Table 3 – Dual Mode TBM Data Type of Tunnelling Shield type Excavation Diameter Length of TBM + Back Up Number of 17” disc cutters Total power Drive unit power Nominal / Max Thrust Nominal / Unlock Torque Shield weight Total weight
Dual mode machine Single shield , passive articulation Ø11.95 m 126 m 71 (cutter heads 1 and 81 (cutter head 3) 8150 kVA 4725 kW 90 000 kN / 110 000 kN 28930 kN.m / 37 000 kN.m 1500 Tonnes 2200 Tonnes
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The main challenge was to organise the design, fabrication and delivery of every cutter head according to the planning of operations, and to perform the exchange operation in sometimes difficult conditions. As an example, the following describes the original cutter head exchange operation executed at Maragall metro station where access directly above the cutter head was not possible. The site configuration is as follows: a shaft is bored 15 m to the side of the tunnel, and a gallery (6.5 m in width and 15 m in height) is excavated using traditional methods so as to communicate with the main tunnel. This gallery is further equipped with two tracks on which a self-propelled truck can move. Upon arrival of the TBM, its cutter head emerges in the communication gallery. The current cutter is disconnected from the drive unit and positioned onto the truck with the help of hydraulic jacks. The truck can then be moved below the shaft opening, from where a crane hoists the cutter head up to the surface. Installing the new cutter head follows the same principle in reverse sequence. The complete exchange operation was executed in 3 weeks.
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