To provide a method for stabilizing a water collecting filtration layer, by which the water intake function of the filtration layer can be kept over a long period of time.
This method is applied to a water collecting pipe 12 buried in the submarine ground 10 for taking in seawater. A filter layer 14 and a sand layer 16 which constitute the filtration layer are formed on the outer periphery of the pipe 12. The layer 14 is composed of a crushed stone layer 14a and a particle size-adjusted crushed stone layer 14b. The layer 14a is formed on the outer periphery of the pipe 12 to have a prescribed thickness. The layer 14b of a prescribed thickness is formed on the layer 14a. A layer 16 of a prescribed thickness is formed on the layer 14b. The mutual ratio between the amount of a soil particle having a specified particle size of the layer 16 and that of the crushed stone having the specified particle size of the layer 14 is set to satisfy a specified relational expression. The layer 14 allows the permeation of water and has a water-semipermeable structure for hindering the permeation of the soil particles of the layer 16.
OKAMOTO HIDEYASU