Double shield pair to head to Spain13 April 2005
In late February, German manufacturer, Herrenknecht, was preparing to ship two 3.37m o.d. doubleshield hardrock TBMs to the Jucar-Vinalopo Water Transfer Project in Spain.
The TBMs will be used to drive four tunnelled sections, with a combined length of 23.3km, by NESCO and OHL/UTE Cuesta Vinalopo. Designed for hardrock formations, the machines are expected to bore through dolomites, limestones, siltstone and marl as they complete the individual legs between 4km and 7.3km long. The 170m long machines will be operated in conventional or continuous mode depending upon conditions.
Competent rock will allow the ringbuild to take place behind the machine, concurrent with excavation and with consequently high production rates. When poorer quality ground is encountered such as in a fault zone, the machine can be driven as a conventional shield, with ringbuild taking place as a serial activity on the workcycle. The reduced productivity is offset by the enhanced safety for the workforce, equipment and the integrity of the tunnel itself. Although this approach is not revolutionary in itself, the incorporation of it into such a small diameter TBM is what provided the real challenge for Herrenknecht's engineers.
Following a workshop inspection of the machines by the scheme's client and contractors in late February, the TBMs are being disassembled for shipping. Tunnelling is planned to start in the spring on the site at Ayora in Greater Valencia. Upon completion, the Jucar-Vinalopo scheme will transport 80 million cubic metres of water annually to the Mediterranean coastal areas by means of a 67km long pipeline. The river Jucar basin is one of the few places in Spain where water reserves are greater than demand and it is well placed to assist in meeting water demands in the tourist areas.