SOIL AND SAND SEAL IN SHIELD EXCAVATOR

PURPOSE: To restrain heating at a lip seal by a method wherein heat-responsive members which deform, in accordance with rise of the temperature, so as to warp the lips toward the side receiving the pressure of earth are mounted at the inside or the surface of the lips of a flexible lip seal. CONSTITUTION: Heat-responsive members 13 are mounted by embedment, with appropriate intervals provided in the circumferential direction of a seal, to the inside of each of lips 12a of a lip seal 12 formed of a flexible sealing material. Then, the lip seal 12 with the heat-responsive members 13 mounted thereon is mounted on a shield main body 1 with a seal repressor 14, and the lip front ends 12b are pressed against a cutter wheel 2 by the cutting face water pressure P working on the lips 12a. In the case where the temperature at the seals rises to a point above transformation temperature for shape memory alloy, a repulsive force σ generated by deformation reduces the pressing force working on the seal sliding surface by the cutting face water pressure P and heating at the lip front ends 12b is restrained. Thereby, deterioration and breakage of the sealing materials can be prevented and sealing performance can be maintained.