Work on the project had to be paused in June after contractors unearthed an inverted brick arch under the road at Botley Road bridge.
Ground investigations have since revealed that the metre-deep historic arch stretched for 100 metres. Archaeologists believe the arch is part of a Victorian water system, designed to keep river water away from the railway and city.
Work was also paused on Thursday 20th July, when a nearby area had to be evacuated following the discovery of a WWII era hand grenade within the work site, near to the railway tracks. Officers from British Transport Police attended the incident, alongside personnel from Explosives Ordinance Disposal.
A new work schedule has had to be drawn up to remove the brick arch before Network Rail’s contractor, Kier, can continue to divert the utilities below Botley Road. This will involve the installation of piles to support the bridge and a switch to 24/7 working hours. During this work, a temporary drainage system will be in place to manage groundwater, before a new permanent pumping system is installed later in the project.
As of this week, the team on site is working from 7am until 7pm, seven days a week. From Saturday 2nd September they move to round-the-clock working. The revised approach has been agreed with Oxford City Council, in consultation with Oxfordshire County Council.
Network Rail project manager Philip Morton said: "Whilst we knew the arch was there, it’s much larger than our original ground surveys identified, which has added a unique layer of complexity to our ongoing work to upgrade of Oxford station and surrounding areas.
“Due to its potential significance in supporting the bridge, removing the arch from beneath Botley Road is now our biggest challenge, but we’re addressing it as safely and efficiently as possible.
“Following further investigations, our new work plan involves installing piles to stabilise the bridge while we excavate the brickwork before we can continue to divert the utilities.
“Going forward, we will be working day and night so we can gain back some of the time lost, with the majority of the noisy work planned to take place during the day, to minimise disruption for the local community.”
Oxford Archaeology project officer Mark Dodd said: "The historic city of Oxford contains archaeological remains dating back to the prehistoric period, so there's always the potential to discover a bit of history beneath the ground.
“Owing to the existing road, the site itself wasn’t an ideal location for archaeology, so the best approach was for us to be on site while the works are underway. It’s likely the arch was used to help manage the groundwater owing to its low-lying position close to the river Thames and this is an excellent example of a Victorian engineering solution, as seen elsewhere throughout Britain at this time."
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