Undercutting Technique

Reaming Tunnel Boring Machine

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Hat trick in the Uetliberg TunnelState of the art technology

It is a well known fact that me-chanically excavated tunnels are mostly round; and also that this fact is not necessarily desirable. The innovative technology of WIRTH GmbH, with their new Reaming Tunnel Boring Machine in the Uetliberg Tunnel, has re-medied this for the first time.

For the task in the Uetliberg hardrock near Zurich, the WIRTH TBE 500/1440 H-HST combines three elements, which have pro-ven themselves several times in preceding projects.

These elements are reaming techniques; an undercutting technique; and the ability to bore tunnel sections which are not round. This combination offers a range of advantages for the tun-

nel constructor. WIRTH tunnel boring machines that apply the reaming technique are especially suitable for large diameter tun-nels. It is a characteristic of the reaming system that a previously bored smaller tunnel is increased up to its final diameter.

Tunnel boring machines with reaming technique are braced in the pilot gallery, not in the actual tunnel, as it is done with conventional full-face machines. In this way, the reaming machine can be relatively easily adapted to different boring diameters, as modifications are required only on the cutter head not on the machine body itself.

This is done by the attachment of different cutter head arms. In

its original condition the boring diameter of the reaming tunnel boring machine described here was variable within a range of 8.00m to 12.00m.

After its refurbishment for the Uetliberg tunnel project it is ca-pable of coping with a diameter of 14.40m without problems.

Directly in front of the hydrauli-cally driven cutter head, the rea-ming machine is provided with a roof protecting shield to avoid uncontrolled caving in of the pilot tunnel roof, in insufficiently stable rock zones.

Behind the cutter head the full tunnel cross-section is available for rock securing or concreting work.

Reaming Tunnel Boring Machine

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The undercutting technique is known as an especially effective principle. Here, it is not so much the high compressive strength that plays a role but the essenti-ally lower tensile strength of the rock. Profiting from the under-cutting technique distinctly incre-ases the excavating performance per cutter.

Whilst this technology was al-ready applied in a Continuous Miner that WIRTH GmbH had constructed in the early nineties, in cooperation with the Canadian research organisation HDRK, this technical development has now been applied for the first time for the reaming principle.

The WIRTH TBE 500/1440 H-HST is a Reaming Tunnel Bo-

ring Machine capable of boring diameters up to 14.40m. For a reaming tunnel boring project, firstly, a pilot gallery smaller in diameter (e.g. five meters in the Uetliberg) is bored over the whole distance.

Secondly, the reaming machine is braced in the pilot gallery and reams the tunnel with six boring arms, to the final diameter. The new aspects of this procedure are the disk cutters arranged on radially displaceable skids.

During the cutter rotation they are spirally moved to the outside. By varying, radial displacement of the disk cutters, for instance, the circular shape of the tunnel can be flattened to a certain extent; a method reducing the

tunnel cross-section itself and li-miting the material requirement for planing the bottom.

Undercutting profile

Excavated tunnel section with Reaming Tunnel Boring Machine and pilot tunnel

A further advantage is the redu-ced energy consumption, as the rock is broken against a free sur-face and, therefore, in coarser cuttings compared to conventio-nal tunnel boring machines.

The short cutter head construc-tion allows securing work of the tunnel directly behind the face.

A further advantage, in compari-son to the conventional method, is the careful excavation and the depth of spacing, which is re-ad-justable at any time, and adap-

ted to the geology.For 20 years the City of Zurich has been planning a large by-pass – the West bypass, which includes two parallel tunnels 4.4 kilometres in length through the Uetliberg and the Ettenberg.

Based on the geology (a mixture of unconsolidated soil and rock) at first, the use of a mixed shield machine was taken into conside-ration, but after the preparation of a risk assessment this possibi-lity was ruled out. Whilst for the difficult unconsolidated sections

the choice was a core construc-tion, decision was made for blasting excavation in the rock section Eichholz.

The most favourable solution for the 2,800 metres long rock gallery, in the Uetlibergtunnel, was the WIRTH, TBE 500/1440 H-HST reaming tunnel boring machine, modified to work with the undercutting technique.

Both tunnels were initially bored to five metres in diameter, by means of a WIRTH TB III 450 E. The work for the first tunnel star-ted early in May 2002, and the second tunnel started in the last quarter of the year 2002.

In April 2003 the Reamer star-ted in the westbound tunnel, finishing on the 1st of February 2005, with the best rate of 16.5m excavation achieved in one day.

After refurbishment and removal, the TBM started the eastbound tunnel at the beginning of June 2005, and is now aiming for even better rates of excavation with the second drive.

WIRTH GmbH · Kölner Str. 71-73 · D-41812 Erkelenz · Phone +49 2431 83-0 · Fax +49 2431 83-267 Internet: www.wirth-europe.com · E-mail: info@wirth-europe.com

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Cutter for undercutting techniqueUndercutting head for boring diameter of 14.40 m