Abstract
　Damages of coastal dikes and seawals are almost ccaused subsequentl to scour in the toe and to suck out in back-filling soil and sand. Coastal dikes and seawalls protect the land from wave action by the concrete wall and back-fill. Development of the caves in back-fill reduces the stability of dikes and seawalls. It is, therefore, important to know actual conditions of the caves. This report researches about actual conditions of the caves in back-fill of dikes, and seawalls along Yoshikawa, Akaoka, Kishimoto Coast, about 4.4 km east from the Monobe river in Kochi prefecture.
　It was confirmed that the caves have a developing tendency, when the width of the beach in front of seawalls is narrow and their foundations are exposed. The depth of the largest cave in the investigated ones is about 4.4 m. The seawall that includes this cave will be easily destroyed by wave pressure.

【キーワード】：海岸護岸・堤防，裏込め土砂，吸い出し

*愛媛大学大学院連合農学研究科
United Graduate School of Agricultural Sciences, Ehime University
**高知大学農学部
Faculty of Agriculture, Kochi University