Reaming Tunnel Boring Machine Undercutting Technique

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Cordelia Elliott
6 years ago
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1 Reaming Tunnel Boring Machine Undercutting Technique

Hat trick in the Uetliberg Tunnel State of the art technology Reaming Tunnel Boring Machine It is a well known fact that mechanically excavated tunnels are mostly round; and also that this fact is

2 Hat trick in the Uetliberg Tunnel State of the art technology Reaming Tunnel Boring Machine It is a well known fact that mechanically 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 remedied 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 proven themselves several times in preceding projects. Seite 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 tunnel constructor. WIRTH tunnel boring machines that apply the reaming technique are especially suitable for large diameter tunnels. 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 capable of coping with a diameter of 14.40m without problems. Directly in front of the hydraulically driven cutter head, the reaming 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.

Excavated tunnel section with Reaming Tunnel Boring Machine and pilot tunnel The undercutting technique is known as an especially effective principle.

Profiting from the undercutting technique distinctly increases the excavating performance per cutter.

3 Excavated tunnel section with Reaming Tunnel Boring Machine and pilot tunnel 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 essentially lower tensile strength of the rock. Profiting from the undercutting technique distinctly increases the excavating performance per cutter. Whilst this technology was already 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 Boring 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 limiting the material requirement for planing the bottom. Undercutting profile Seite

A further advantage is the reduced energy consumption, as the rock is broken against a free surface and, therefore, in coarser cuttings compared to conventional tunnel boring machines.

A further advantage, in comparison to the conventional method, is the careful excavation and the depth of spacing, which is re-adjustable at any time, and adapted to the geology.

4 A further advantage is the reduced energy consumption, as the rock is broken against a free surface and, therefore, in coarser cuttings compared to conventional tunnel boring machines. The short cutter head construction allows securing work of the tunnel directly behind the face. A further advantage, in comparison to the conventional method, is the careful excavation and the depth of spacing, which is re-adjustable at any time, and adapted to the geology. For 20 years the City of Zurich has been planning a large bypass 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 consideration, but after the preparation of a risk assessment this possibility was ruled out. Whilst for the difficult unconsolidated sections the choice was a core construction, 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 started early in May 2002, and the second tunnel started in the last quarter of the year In April 2003 the Reamer started 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. Undercutting head for boring diameter of m Cutter for undercutting technique WIRTH GmbH Kölner Str D Erkelenz Phone Fax Internet: info@wirth-europe.com B 311 e Technische Änderungen vorbehalten

N4.1.5 Uetliberg Tunnel

N4.1.5 Uetliberg Tunnel The world's largest tunnel bore extender (TBE), which excavates the molasse by undercutting, was commissioned on April 11, 2003. As already reported at the ITA 2003 in Amsterdam,