Abstract
The Roughcastle tunnel is 147 m long and forms part of the Millennium Link connecting the Forth and Clyde Canal and the Union Canal at Falkirk, Scotland. The tunnel was constructed in a mixed face of stiff Glacial Till overlying Lower Coal Measures that comprise interbedded sandstones, mudstones and coals of varying strength. An unfilled, abandoned stoop-and-pillar fireclay mine underlies the tunnel at shallow depth. Boreholes were drilled into the mine to ascertain the rock quality in the roof and pillars and ultrasonic surveys were carried out to determine the condition of the workings.
Risk assessment models indicated that the risk of roof beam failure and collapse chimney initiation in the sandstone or siltstone was extremely low in the current conditions, but the risk of beam failure when mudstone was the roof rock was high. The measures adopted in the design to ensure the structural integrity of the tunnel and the construction techniques employed are described with particular attention to the single-pass sprayed-concrete lining technique.
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