LAYING EFFECT OF BREATHABLE . WATER PROOF SHEET ON RIVER DIKE CONSIDERING HEAVY RAIN AND AIR BUBBLE

Abstract

Based upon numerical analysis, the damage of a river dike caused by a localized torrential downpour is presumed to be related to the saturation of the dike, due to seepage water from the dike surface and blow off of pore air (air blow) following a rise in the seepage line in the dike. Since a river dike located at the downstream, where urbanization has been in progress, is composed of sandy soil consisting mainly of soft and fine particles, the river dike is considered to be easily damaged by pore air that has been enclosed within the dike body. In this study, by performing experiments using a dike model equipped with a rainfall generation apparatus, the behavior of a pore air mass captured by rainfall seepage and a rise in the river water level was investigated. When no countermeasures had been taken to the dike, a rise in the pore air pressure and an air blow phenomenon were confirmed following rainfall seepage and a rise in the river water level. When seepage prevention measures using an unbreathable - waterproof sheet had been taken, the pore air pressure below the sheet rose. When seepage prevention measures using a breathable - waterproof sheet had been taken, the effect of preventing rainfall seepage and that of reducing the pore air pressure were confirmed.