Tunnel Shield an internal frame, or shield, used to support loose earth in a tunnel while digging First used in a tunnel in 1825, to excavate the Thames Tunnel, London, England

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The inspiration for the tunnel shield was a bizarre creature called the helmet-headed shipworm. While in prison for debt, a French engineer named Marc Brunel watched the worm bore through wood, using the hard shell on its head as a shield. As it tunneled into the wood, the worm excreted a substance that formed a rigid lining behind it. Brunel figured out a way to copy this idea on a large scale. He used a large iron frame to keep the gooey sides of a tunnel up while masons lined the inside with brick.

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