| 摘要 |
PROBLEM TO BE SOLVED: To prevent the deterioration in the water permeable function of a filter layer. SOLUTION: A water feeder has an expandable water feeding pipe 22, a hydraulic jack 24, and a water introducing part 26. The water feeding pipe 22 is a double tube composed of an inner tube 22a and an outer tube 22b, and is open on both ends. The water introducing part 26 has a easing 26a, the filter layer 26b, a biodegradable sheet 26c, and a biodegradable viscous substance 26i. The filter layer 26b is housed in the casing 26a. The sheet 26c and the viscous substance 26i are decomposed by a microorganism such as bacteria. The sheet 26c is locked at the outer peripheral edge on the easing 26a so as to cover an outside surface of the filter layer 26b housed in the easing 26a. The viscous substance 26i is filled in the filter layer 26b so as to fill up a clearance space of the filter layer 26b.
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