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University of Zagreb Engineering Geologists Perform Forecasting and Protective Monitoring of the Kostanjek Landslide

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central part of landslide. Today there are still more than 300 homes and associated infrastructure on the moving landslide mass. Since the movement started, it has resulted in significant damage to both residential and commercial buildings and properties. Martin Krkač, assistant professor at the Faculty of Mining, Geology and Petroleum Engineering of the University of Zagreb, explains that despite extremely slow landslide movements over the past 50 plus years, the risk surrounding the landslide is still high. Since 2011, scientists have been working to estimate these risks by acquiring new knowledge about landslide movements. subscription gives users the flexibility to choose the level of accuracy to suit their application needs from meter level to centimeters. There are several unique characteristics of the Kostanjek landslide that made monitoring challenging including finding adequate positions to monitor within the landslide, providing adequate electrical power supply, gaining permission from local citizens and city authorities to monitor the area. Cheaper solutions, such as total station, were not possible, because landslide morphology disable the line- of-sight visibility between total station and prisms. The Kostanjek landslide is the largest landslide in the Republic of Croatia. It is activated by mining activities in 1963, i.e., undercutting of the marly slopes and uncontrolled blasting. Excavation of the total volume of 5.1*106 cubic m. in the marl quarry caused slope instability of 32*106 sq. m. volume and superficial movement in the wider residential area placed around abandoned open pit. Scientists report the width of the displaced mass is some 960 meters, and the total length of the landslide is 1.26 kilometers. The depth of the sliding surface is 62.5 meters in the Between 2011 and 2014 the landslide scientists from Zagreb, Rijeka and Japan, Geomatika Smolčak Ltd. and Trimble Inc. developed and implemented a real-time monitoring system to monitor and predict the movement of the landslide that got around the problem of line-of-sight. GNSS receivers and various types of geotechnical sensors have been installed. All movement sensors are connected to the core of the monitoring system, the Trimble 4D Control monitoring software. The software processes, visualizes and forecasting models by scientists also required extensive monitoring of causes of landslide movement (precipitation and groundwater level). Trimble 4D Control™ monitoring software, Trimble NetR9™ GNSS reference receivers. Precise GNSS monitoring - Sixteen Trimble NetR9 receivers collect GNSS data and deliver it in real time via routers to Trimble 4D Control software for real-time landslide monitoring. Remote sensor management and visualization - City authorities, scientists and other project stakeholders can monitor and visualize the landslide movement, remotely from a web portal using Trimble 4D Control software. Building more reliable landslide movement model - The landslide monitoring system aids in the development of more accurate movement models which enable forecasting of landslide movements. Kostanjek landslide movement predictions are based on empirical models, combining landslide movement parameters with other parameters of landslide causes such as groundwater levels and precipitation. Figure 1. Trimble NetR9™ GNSS reference receiver. "We analyze its displacements, velocities and accelerations depending on influence of precipitation and groundwater level changes," said Dr. Krkač. "The analyses of continuous time series of landslide displacements obtained by GNSS revealed unambiguous sliding of the huge landslide mass in the direction of 60-meter-high cuts in abandoned open pit. Moreover, we identified two movement patterns, slower and faster movements which corresponds to periods of higher precipitation and higher groundwater levels. High quality data enabled quantitative comparison of the relationship between sliding and its causes using advanced statistical models." With these observations the goal is to better predict the displacement based on meteorological prognosis of precipitation. Dr. Krkač explains that the prediction of landslide displacement 24 hour in advance is necessary for early warning of civil protection that are responsible to activate measures of evacuation in case of threatening sliding. Precise GNSS Monitoring Data Mining Activities Caused Slope Instability Solution I N D U S T R Y P R O D U C T W A T C H 2 2 G I S R E S O U R C E S | S E P T E M B E R 2 0 1 8 Results

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