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Works begins on chalk-fall prone rail tunnels in Kent

NEWS

SPECIALLY DEVELOPED tunnel lining plant began work last month on refurbishing the 180-year-old Strood and Higham rail tunnels in Kent.

The £40M, 12 month project is designed to remedy the persistent chalk falls that have disrupted services through the tunnels since December 1999.

Contractor Costain will use Italian designed steel erecting plant with a protective full-tunnel section canopy to install steel ribs at 2m centres.

The machine trims the tunnel profile to ensure it remains outside the kinematic envelope of the track with the additional lining.

The works train will erect the ribs to its rear as it progresses down the twin track tunnel.This process will be followed by a bespoke shuttering system that will enable 350mm thick selfcompacting concrete bays to be cast on to the shuttering. .

This full-tunnel section shutter can automatically retract from the lining before moving on to the next 10m long bay. Each 70m 3bay will be struck within four hours.

Higham tunnel is 1.4km long and Strood tunnel, 60m away, is 2.1km. About 60% of the total length of the two tunnels together is brick lined while the rest is exposed chalk.

In the past temporary repairs have been been carried out in response to localised chalk falls triggered by vibration and water percolation. In December 1999, a chalk fall caused a passenger train to derail.

In June 2000 a shaft collapsed, closing the tunnel. Since July 2000 the tunnel has operated with a 20mph speed limit. The tunnel will remain closed for the rest of this year and passengers will continue to endure a replacement bus service.

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