Abstract
The repair of tunnel linings on the Hong Kong Mass Transit Railway by means of a unique robotic system was the subject of the British Tunnelling Society Meeting at the Institution of Civil Engineers on November 24, 1994. Inspections during the mid 1980s revealed the need for repair in certain tunnels, particularly where aggressive sea water penetrating the ground was slowly percolating through the precast concrete tunnel linings, causing extensive spalling. A repair method had to be devised, which could be executed within the daily 5 o'clock shut down period to avoid disruption to railway operation. The concept eventually established after considerable research and trials was: To seal existing leaks; To remove cover concrete to the inside face reinforcement; To remove the corroding near face reinforcement wherever possible; To replace the existing cover concrete with a thicker (75 mm) layer of high density, low permeability (<1 x 10 (-12m/s) shotcrete to induce saturation of the existing lining to create a nil oxygen environment, thereby stabilizing corrosion.
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