This study investigated deformation behavior that has been recognized as a precursory phenomenon of slope failure. The slope failure tests were conducted in which the deformation behaviors of model slopes were measured. The surface displacement of a sand model slope was measured using an invar wire extensometer, and the underground displacement was measured with a connected inclinometers together (or an inclinometer). The results indicated that the surface and ground displacements behaved similarly. The results also clarified the underground deformation behavior under different stress conditions. In addition, the results of the underground displacement measurements using the inclinometer was applied a prediction method using the reciprocal of velocity, and this paper showed the effectiveness of underground displacement measurement and the prediction of slope failure by the inclinometer.

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  The prediction of the slope failure time is evaluated by a method based on creep velocity of the surface displacement of the slope in normal engineering. However, such a method has problems in that the velocity of the tertiary creep is affected by many different conditions and it is difficult to judge the stage of the tertiary creep.
  This study examined the change over time of the slope displacement rate (velocity) and derived a criterion for tertiary creep. Model tests were conducted on a large-scale sand slope during periods of rainfall. The test results indicated that the change point of the slope displacement rate occurs at the same time at all positions of the sliding soil mass. In addition, the study showed the effectiveness of the judgment criteria using the slope displacement rate changes in a rainfall-induced slope failure.

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