The failure time of a slope is predicted by a method based on creep failure theory for slope displacement on natural slopes, embankments, and cutting slopes. These prediction methods employ several equations based on the relationship between the displacement rate (displacement velocity) and time. However, such methods harbor problems because the shape of the tertiary creep curve is affected by many conditions, and it is difficult to identify the phase of tertiary creep. This study examines the time change in the displacement rate of the slope and derives an index for identifying the phase of tertiary creep. Two models of large-scale composite granite slopes were tested by using a large-scale rainfall simulator. In the experiments, the slope displacements were monitored in real time. From these results, inflection points were found in the velocity of the slope displacement. It was found that the corresponding inflection points at different locations in the sliding soil mass occurred with the same timing. This paper discusses the effectiveness of the prediction method for slope failure time by using the inflection points of displacement rate in real-time monitoring records.

1. [1] H. Kobashi and K. Sako, “The present state of slope monitoring techniques by various measurement instruments,” Geotechnical Engineering Magazine, The Japanese Geotechnical Society, Vol.55, No.9, pp. 7-11, 2007 (in Japanese).
2. [2] T. Uchimura, I. Towhata, L. Wang, and I. Seko, “Simple and low-cost wireless monitoring units for slope failure,” Proc. of the First World Landslide Forum, Int. Consortium on Landslides (ICL), pp. 611-614, 2008.
3. [3] Y. Ikegami, “Development of wireless sensor network and monitoring of an active slope,” Geotechnical Engineering Magazine, The Japanese Geotechnical Society, Vol.56, No.11, pp. 16-19, 2008 (in Japanese).
4. [4] M. Saito and H. Uezawa, “Failure of soil due to creep,” Proc. of the 5th Int. Conf. on Soil Mechanics and Foundation Engineering, Vol.1, pp. 315-318, 1961.
5. [5] M. Saito, “Forecasting time of slope failure by tertiary creep,” Proc. of 7th Int. Conf. on Soil Mechanics and Foundation Engineering, Vol.2, pp. 677-683, 1969.
6. [6] T. Fukuzono, “A method to predict the time of slope failure caused by rainfall using the inverse number of velocity of surface displacement,” Landslide Socociety, Vol.22, No.2, pp. 8-13, 1985.
7. [7] T. Ishizawa, T. Danjo, N. Sakai, and T. Fukuzono, “Study of prediction method of slope failure in rainfall using sensing – Effectivity of slope monitoring using Connected type multisensor –,” Proc. of Geokanto2016, The Japanese Geotechnical Society, CD-ROM, Disaster prevention7-1, 2016 (in Japanese).
8. [8] T. Ishizawa, N. Sakai T. Moroboshi, and T. Fukuzono, “Effective-ness of underground displacement measurement using inclinometer for prediction of slope failure,” The Journal of Japan Landslide Society, Vol.50, No.6, pp. 256-267, 2013 (in Japanese).
9. [9] T. Fukuzono, “Prediction of Failure Time of a Slope by Reciprocal of Mean Velocity – Study on Prediction of Slope Failure (3),” Report of the National Research Institute for Earth Science and Disaster Prevention, Vol.46, pp. 45-81, 1990 (in Japanese).