| 摘要 |
A sheet of material is folded in opposite directions around a first set of equidistant parallel fold lines to form a second set of equidistant parallel fold lines which intersect with each other and with the first lines at substantially opposing but equal angles. Successive rhomboids are formed between every second first fold line and the opposing corners of each rhomboid in the respective row of rhomboids contacts every second first fold line, whilst an intermediate first fold line extends through the other corners of the rhomboids in this row. Successive rhomboids in each row are folded along a central fold line to form a convex region in between two triangular sub-regions separated by this fold line. The sheet is pleated about the fold lines so that the first fold lines are substantially parallel offset relative to each other, so that the sheet adopts a curved shape forming the walls and roof of the tunnel. The rhomboid pattern extends along a central region of the sheet width defined by the first fold line direction and the first fold lines extend over the entire width of the sheet. The edges of the sheet located outside the central width region are pleated by folding them along the first fold lines and the combined length of the pleated edges in the sheet width direction is greater than the distance between the opposite ends of the remaining central width region. The pleated edges overlap with each other and have parallel length axes so that they form a pleated floor structure. |
