Re-alignment of Bletchley flyover underway to enable high-level platforms to be built
SOME of Europe's largest mobile cranes have been deployed to remove sections of the Bletchley flyover spanning the West Coast Main Line as part of preparations for East West Rail (EWR) during April and May.
The flyover was a product of
BR's 1955 modernisation plan. Construction of the 37-arch Bletchley flyover started in 1959, with it opening in 1961, but only after being load tested by eight steam locomotives!
It never carried regular passenger traffic, being built for freight travelling across England, avoiding congested routes via London, and remained underused for many years before being mothballed in October 1993.
The line forms a key part of the plan to restore train services between Oxford and Milton Keynes/Bedford. It returned to operational status in 2006, along with a mile of track west of Bletchley, ending in a new loop at Newton Longville, but was again taken out of use in 2019, the track lifted and ballast removed exposing the flyover's concrete deck for removal.
4D software
This location forms Area 2C of the East West Rail Project, which will result in high-level platforms built on the flyover and a new eastern entrance to the station.
To provide enough space for the platforms, 14 flyover arches alongside and over the WCML will be replaced, with the alignment moved slightly east.
Before the first span was removed, detailed calculations and simulations were carried out using 4D building-information modelling software. Constant monitoring equipment was then fitted to the flyover spans and supporting piers.
Before removal, each span and crossbeam had to be cut free from the bridge deck and supporting piers then lifted using synchronised hydraulic jacks installed underneath each 300-ton span.
It was estimated these could move to a maximum of 5mm before they might start to fracture under stress.
A lifting beam was fixed at both ends of a span connected to pattress plates on its underside.
Span 17 was the first to be removed using a 750-ton counter-balanced crane on
April 22 followed by spans 18 and 19 on April 25 and May 3, respectively. The estimated span weight proved to be within 2% of the actual weights.
Volker Laser has undertaken all the jacking works, with project leader Jeff Booth saying: "The spans' removal on the west side, but not over the WCML, were used as atrial followed by a review carried out on everything we did on those spans to enable the lift.
Safety reports
"We have also undertaken safety justification reports to prove our methodology prior to working on the spans over the WCML as this type work has never been done before. This is to mitigate risk to the WCML in every aspect and avoid closing it:'
A further eight sections spanning the West Coast Main Line were removed over three weekends in May, with the spans directly over the WCML due to be removed over six weekends in July and August.
"It never carried regular passenger traffic, being built for freight travelling across England, avoiding congested routes via London, and remained underused for many years before being mothballed in October 1993."