Mr Pack said that officials found an explosive device inside the pipe, as well as another device inside the bunker.

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Inside the riser pipe is a space about half a meter in diameter, large enough to hold the spinning drill pipe and bit and to allow the return flow of drilling fluid.

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The material then bonds to the inside of the pipe and the resin cures or hardens, creating a new pipe within the pipe and restoring the integrity of the drain or sewer.

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As the liner is inserted into the pipe, it is turned inside out and forced through using water or air pressure.

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After the rescue, authorities found the pipe packed with explosives along with another explosive inside the bunker itself, authorities said.

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