LINING.
Either iron or masonry may be used for lining shield-driven tunnels but present practice is almost universally in favor of iron lining. As usually built, iron lining consists of a series of successive cast-iron rings, the abutting edges of which are provided with flanges. These flanges are connected by means of butts, the joints being packed with thin strips of wood, oakum, cement, or some other material to make them water-tight. Each lining ring is made up of four or more segments, which are provided with flanges for bolted connections similar to those fastening the successive rings. Generally the crown segment is made considerably shorter than those forming the sides and bottom of the ring. The erection of the iron segments forming the successive rings of the lining may be done by hand in tunnels of small diameter where the weights to be handled are comparatively light, but in tunnels of large size special cranes attached to the shield or carried by the finished lining are employed. The construction of the iron lining for the Hudson River tunnel is illustrated in [Chapter XX.], and that for the St. Clair River tunnel is shown by [Fig. 137].
Part Transverse Section.
Longitudinal Section.
Fig. 137.—Cast-Iron Lining, St. Clair River Tunnel.
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