The Variation of Pore Water Pressure on the Landslide Slip Surface due to Seepage of Rain

Abstract

Rainwater percolates slowly downward through the parts of high permeability in the layers and finally it is deposited near the landslide surface.According to the general consideration, a ladslide is caused by the pore water pressure due to the deposition of ground water on the landslide surface. Furthermore, it should be noted that when rainwater seeps downward in the layers, which are mostly unsaturated, air in the void of the unsaturated parte of the layers is compressed by the seepage pressure due to the descent of the wetting front; as a direct effect upon the pore pressure on the landslide surface.The results of model tests for the phenomena as described above, are as follows;(1) When the wetting front descends into the unsaturated layers, the pore water pressure equivalent to 17-83% of the seepage pressure occurs on the landslide surface.(2) When the artesian pressure is acting on the landslide surface prior to the descent of the wetting front, the water pressure on the landslide surface increases slowly, provided that the wetting front seeps down in the unsaturated layers, and as time proceede, the pore water pressure will be equal to the seepage pressure in value.