Grouting to remove piles from a tunnelling machine cutter-head

摘要

This paper provides a summary report on measures taken to remove embedded steel 'H' pile obstacles from the cutter head of an advancing tunnel-boring machine. The piles were part of the soil-mixing retaining wall built for the cut-and-cover tunnel construction of a Taiwan high-speed rail tunnel and a Taiwan railways administration tunnel, which were directly above the mass rapid transit tunnel that was to be constructed. The collision zone between the boring machine and piles was below groundwater level and was approximately 23 m below the ground surface in a silty sand layer. To remove the piles safely from the cutter head, horizontal grouting from two adjacent work pits was conducted for waterproofing and solidification purposes. By controlling the amount of soil being flushed out during the grout hole drilling first, and also the pressure used for grouting later, the measured tunnel settlement resulting from grouting was negligible. Because of the favourable watertightness of the grouted zone and the dewatering influence of a nearby construction site, pile removal was conducted under particularly dry working conditions. In total, 12 piles were identified in the collision zone and were successfully removed from the cutter head by hand tools.