Digging for monitoring gold: in-tunnel monitoring during the Crossrail Paddington Station box excavation

Increasingly on large infrastructure projects, programme constraints require conflicting construction activities, often by different contractors, to be carried out concurrently. This was the case during construction of the new Crossrail Paddington Station in London.

The Crossrail Western Tunnels comprise twin-bored tunnels through central London constructed by tunnel boring machine (TBM). In order to meet a tight construction programme, a ‘TBM first’ strategy was adopted, whereby the tunnels were driven first and the stations were built around them, with the temporary rings broken out as the excavation advanced.

The Crossrail Paddington Station box was located 880m along the 6850m twin bore tunnel drive from the Royal Oak Portal to Farringdon Station. Design stage programming suggested that waiting for the tunnel drives to be completed before excavation of the box would not only have significantly delayed construction of the station but would have resulted in delay to project completion. Similarly, as Paddington station was located so close to the start of the tunnel drives, completion of the box construction before commencement of tunnelling was not feasible.