Tunnelling machine with three telescopic cylinders behind cutting head - has sequentially operated jacks advancing cylinders and head after concrete injection

摘要

The tunnelling machine has a cylindrical cutting head consisting of a ring of concrete inside a metal lining. The front face slopes inwards and the periphery carries a pointed cutting ring. This is forced forwards by a set of three cylinders powered by a system of jacks, the cylinders being operated sequentially to move telescopically. Between the head and the first cylinder is a ring of smaller guide jacks. A layer of clay is injected through passages along the first cylinder around the second cylinder, when the first cylinder has been forced forwards by the main jacks. A layer of concrete is injected around the third cylinder, and the cylinders are then progressively advanced.