GPS is now being used widely for monitoring rock displacements, and it has been a useful tool for various rock engineering projects. The most important technical issue for the practical use of GPS in monitoring displacements is to perform real-time and precise monitoring even under adverse observation conditions, i.e., steep slopes, the existence of trees and walls above/around the sensors, bad weather conditions, etc. The authors and their colleagues have developed a precise real-time displacement monitoring system using GPS and have established a method of data processing which can automatically reduce the errors caused by meteorological factors and obstructions above the antennas.

In this research, the GPS displacement monitoring system is applied to monitor the displacements of an unstable steep slope for the safe management of a national road in Japan over the long term. Three-dimensional displacement monitoring results are shown.

1. Introduction

Monitoring rock displacements is important to assessing the stability of rock slopes. The Global Positioning System (GPS) can continuously measure three-dimensional displacements over extensive areas. The "ISRM Suggested Method for Monitoring Rock Displacements Using the Global Positioning System" was proposed (Shimizu et al., 2014) as technology which can be used by anyone.

In this research, the GPS displacement monitoring system developed by the authors is applied to assess the stability of an unstable steep slope along a national road in Japan. Since local slope failures have occurred in the slope several times over the last 20 years, displacement monitoring has been conducted by borehole inclinometers and surface extensometers. Some of the instruments, however, have occasionally not worked due to large deformations, and it has become difficult to perform the monitoring continuously. In order to overcome such trouble, the GPS monitoring system has been applied (Furuyama et al., 2014). In this paper, the results of three-dimensional displacement monitoring using GPS are shown, and the applicability of this system for assessing slope stability is discussed.

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