| 摘要 |
PROBLEM TO BE SOLVED: To improve the function of an earth cover layer by forming the grain size of earth of the earth cover layer put on an underground tank so as to become finer as it goes up. SOLUTION: A conglomerate layer of which grain size gets finer as it goes up from a roof 4 side, a sand layer, and a cohesive soil layer are laid on a low temperature underground tank. The upper side thereof is covered with an earth cover layer 6 provided with a surface soil layer 6d for vegetation. A peripheral part 6K encircling the upper part of the side wall 3b of the tank 10 is provided in the conglomerate layer, and the outer peripheral side of the cohesive layer is made wider than the outer periphery of the conglomerate layer and the sand layer, and the upper part of the peripheral part 6K is covered with a skirt 6S. Since the earth cover layer 6 has finer grains as it goes up, it prevents the saturation zone from spreading to the upper part from the underground water level owing to the capillary phenomenon and also prevents the underground water from penetrating from the lower part of the coverting layer. Further, since the water-permeability of the cohesive layer is poor, rainwater flows to the lower ground along the outer peripheral slope face 6P of the skirt 6S to prevent the humidity in the layer 6 from increasing. In this way, the earth cover layer can be prevented from freezing and a stable earth cover layer without ground deformation can be formed.
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