GRP Pipe as Protection Pipe for LNG Pipeline at Isle of Grain power station

For the first 2 drives the pipe lengths were two 3 m pipes behind the shield with the remaining pipes being 6 m long. Every third pipe was fitted with two bentonite injection points. The 144 m long drives were at relatively shallow depths and parallel to each other so that they could share the same jacking pits. Shortly after starting the second drive an obstruction was encountered that stopped the machine, which was eventually found to be a large steel pipe crossing the top of the proposed alignment. This investigation involved a hand constructed adit cut through from the first drive in front of the second drive to determine the extent of the obstruction. The remedial action was to reverse the machine out by winching, to remove the first few pipes while at the same time backfilling in front of the shield and at the same rate using low density concrete to stabilize the void left. The drive was then restarted 1 m lower so as to go under the existing pipe.The pipes in the third and fourth drive had to be installed at a depth of 23 m because they had to cross a gas main (2x DN 1400, main supply from London) a safe enough distance below it.