Tunnel lining form

Claim 1

In combination with a tunneling machine which excavates a tunnel in a subterranean structure and provided with means for lining a wall of the tunnel immediately beind the machine with concrete, a removable tunnel casing adapted to be emplaced behind said machine to define a space with said wall to be filled with concrete, said casing commprising: a plurality of removable segmented generally cylindrical tunnel casing sections disposed substantially in axially end-to-end relation and formed with respective annular flanges at the axial ends of said sections whereby proximal flanges of successive casing sections define the respective joint forming a gap with a variable gap width, said casing sections being removably disposed in said tunnel such that a section can be moved from an upstream end of the casing to a location immediately behind said machine; sealing means on at least one of said casing sections at each of said joints for sealing the respective gap against incursion from the direction of a tunnel wall; respective drawbolts angularly spaced at each of said joints for drawing the proximal flanges thereof toward one another to varying distances depending upon the path of the tunnel; and angularly equispaced compression spacers disposed between and axially bridging the proximal flanges at each joint for variably establishing respective spacings between said proximal flanges at the respective spacers and between portions of the proximal flanges and being blockable to maintain the said spacing under compression forces whereby the progressive advance of the casing through said tunnel permits the casing to be oriented to tunnel curves with said sections and being blockable to maintain the said spacing under compression forces.