SEGMENT

PURPOSE:To obviate the need for supporting and perform an open excavation of ground by, when a segment of a side wall is disassembled and shield tunnels are joined, releasably incorporating a segment piece into a frame before disassembling the segment. CONSTITUTION:Parallel and adjacent tunnels are excavated by means of a shield excavator and a lining of segments 1 is formed to construct a shield tunnel having rectangular section. In this case, the shield tunnel is constructed in such a manner that the segments 1 are continuously applied to opposing surfaces of the tunnels only and ordinary segments are applied to the remainder of the surface. After the shield tunnels are constructed, the ground within a proper range is improved and water is sealed and the segments 1 of the opposing walls in a longer side direction are disassembled, wherein disassembling is performed by removing segment pieces 5 from within a frame 4 and the vertical load is born by column members 2 and beams 3. And sumultaneus with the disassembing of the segment 1, an earth retaining steel plate is provided between the shield tunnels to enable an open excavation of the ground.