The present invention relates to shape deformable materials, which are capable of being deformed, storing an amount of shape deformation, and recovering at least a portion of the shape deformation when exposed to a humid environment. Since the shape of the excavating surface on the work face formed by the cutter is set by a curvature, upon advance of the shield machine by boring through the tunnel wall, the tunnel wall to be excavated, the shape of which is cylindrical, can be cut into by opening a hole which extends diametrically outward from the central portion of the cutter. A step is also performed to form an electrically conductive contact plug that extends in the contact hole, is electrically coupled to the lower barrier layer and protrudes above the electrically insulating layer.