Screw conveyors are useful ... so the hole is a bit larger than the pipe that forms the center. They’re then given a slight spiral (think a lock washer) by walloping with a sledgehammer.

An African mine will be among the first adopters of innovative Rail-Running Conveyor (RRC) technology, commercialised by FLS in collaboration with Australia’s University of Newcastle ...

Large-diameter dual-channel slurry TBM “CREC 1503” manufactured by CREG (China Railway Engineering Equipment Group Co., Ltd.) ...