Abstract
The drainage methods are commonly used for a prevenfive measures against the landslide. The drainage works at Hirayama landslide area had been practiced by the drainage tunnels and weep holes.
The quantity of ground water, 400l/min, from the tunnels have been flowing for three years, but the sliding is occured by every heavy rain.
Therefore, it is the purpose of this paper to point out that it is difficult to prevent the landslide by the drainage works. The following became clear after the investigation on the effect of prevention by the drainage works at Hirayama landslide area. The purpose of the drainage works is to promote the consolidation of the disturbed clay layers by rubbing action on the landslide surface. When the degree of consolidation exceed a certain numerical value, the angle of internal friction increases little by little. As the consolidation proceeds, the effect of variation in the pore water pressure appears slowly.
