| 摘要 |
PURPOSE: To maintain positively a drainage function by installing a water permeable layer made of resin or rubber on a single surface of a needle punched non-woven cloth with a specified weight and thickness and specifying an elongation and a coefficient of permeability after the application of a specific fixed load. CONSTITUTION: A resin or rubber-made water conducting layer 3 is installed to a single surface of a needle punched non-woven cloth whose weight exceeds 300g/m<2> and, what is more, whose thickness exceeds 3mm. On one hand, preferably, a hydrophobic resin or rubber-made hydrophobic layer be installed on the other surface. In this case, the following properties are required as a drainage sheet 1: The elongation is 2% and below and the coefficient of permeability in the sheet face direction is 1.0×10-<1> cm/sec and over after the application of a fixed load of 1.5kg force/5cm width for 7 days. The water permeable layer 3 is laid out so that it may face with the subsoil side of an excavated tunnel. Then, spring water from the underground is discharged from the inside of the non-woven cloth outside the tunnel by way of the water permeable layer 3. This construction makes it possible to discharge efficiently spring water from the underground outside the tunnel and cast concrete to a satisfactory extent.
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