Work is being driven forward on the reboring of Farnworth Up Tunnel, on the commuter route between Manchester and Bolton, which is being enlarged to accommodate two tracks and overhead line equipment as part of the North West Electrification Programme.
Despite carrying out extensive ground investigations, the project team was faced with considerable challenges early in the excavation when the tunnel was twice inundated by running sands but, following difficult remedial works, progress since has been uninterrupted.
Key to the reboring is an open-face shield – a machine built in modular form by an engineering firm in Oldham and then assembled on site. It includes two telescopic cutting booms which are used to excavate material from the upper and lower halves of the working face; behind them is a hydraulic system to install the concrete lining.
Once the tunnelling is complete, the machine will be dismantled and its launch pit filled before track laying gets underway. Based on current rates of progress, it’s hoped the railway will be restored to full operation by the end of the year.