SOME CONSIDERATION ON THE CAUSES OF CLIFF FAILURES OF RYUKYU LIMESTONE FORMATION IN RYUKYU ARCHIPELAGO AND THE ANALYSIS OF A RECENT CLIFF FAILURE

Abstract

 The authors have performed many investigations on the stability of cliffs with toe erosion in Ryukyu Archipelago. It is found that the degradation of a lot of erosion cliff failure surfaces was almost uniform. For example, a failed cliff with erosion on Sesoko Island was characterized as a three layered structure with different degradation degrees. Therefore, it is necessary to research the causes related to crack propagation and rock masses deterioration using different technique. In this study, we utilized an infrared camera, model experiments using shaking table and a series of finite element analysis. The finite element analyses were carried out by considering a three layered structure with different deterioration states. The site investigations, model tests and numerical analyses revealed that the conditions of degradation should have been different as the time of occurrence of tensile cracks was different in each layer. It has found that the tensile strength of rock mass should range between 0.24 and 0.35 MPa from the collapsed histories.