Development of regular check-up system of slope stability using RTK-GPS

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GPS have realized high precision survey of even a single nail on the ground. Real-Time Kinematic (RTK)-GPS can survey more points in shorter period than conventional static GPS. RTK-GPS could realize "regular check-up system of slope stability" system by detecting landslide precursor movement. Fundamental research was conducted for developing the system using RTK-GPS and obtained following results.1. Stability of RTK-GPS positioning was examined by 24-hrs continuous monitoring at a fixed point. Standard deviation of horizontal positioning was 3 mm. No drifting nor jump was observed. Power on/off test was conducted, however obtained first position dispersed not wider than 1 cm. These results imply high stability of RTK-GPS positioning. Static GPS needs more than 2 hours for positioning a point with precision of smaller than 5 mm, however, 300 epochs in 5 minutes by RTK-GPS 1-second-monitoring show standard deviation of only about 3 mm in North-South and East-West and about 6 mm in Up-Down component. This result means RTK-GPS has enough capability of detecting 5 mm of movement.2. Short-time RTK-GPS survey was repeated in Nuta landslide, Kochi Prefecture over the research period. Results show ; (1) 300 epochs in 5 minutes show only 3 mm of standard deviation even on slopes. (2) Movement vectors of the survey points in Nuta landslide in different landslide blocks show different movement direction. This implies that RTK-GPS can be used for landslide block discrimination.3. Automatic GPS antenna tripod stabilizer was developed using a electronic inclinometer and servo-motor. It can assist RTK-GPS short time survey because it can help setting the antenna exactly above the survey nail on the ground in a minute and keep it within 1 mm during the survey time even on soft ground. This system was applied for patent through Kansai TLO to the Japanese Patent Office.