45 The Grohovo Landslide Monitoring System - Experiences from 18 Months Period of Monitoring System Operating Kristijan Ljutić (1) , Vedran Jagodnik (2) , Martina Vivoda (2) , Sanja Dugonjić Jovančević (2) , Željko Arbanas (2) 1) 4D Monitoring Ltd, Milčetići, Croatia, Milčetići 20, kristijan.ljutic@4d-monitoring.com 2) University of Rijeka, Faculty of Civil Engineering, Rijeka, Croatia Abstract The Grohovo Landslide, the largest active landslide along the Croatian part of the Adriatic coast, is located on the north-eastern slope of the Rječina River Valley. In 2009, the Croatian-Japanese research joint project DzRisk identification and Land-Use Planning for Disaster Mitigation of Landslides and Floods in Croatiadz was initiated and the Grohovo Landslide was chosen as a pilot area for a monitoring system development. A comprehensive monitoring system was designed, consisted of geodetical and geotechnical monitoring equipment. Installation was started in March 2011 and, in a major part, completed till the end of 2011. This integrated monitoring system generally can be divided in two major parts: geodetical consisted of GPS system (9 rovers and 1 master unit), and robotic total station with 24 geodetical prisms; and geotechnical consisted of pore pressure gauges, inclinometers and extensometers. Establishment of the monitoring system was carried out in stages according to monitoring equipment purchasing process and equipment delivery. Installation of inclinometer casings and pore pressure gauges was started in March 2011 while foundations and poles for long span extensometers were completed in May 2011. Main part of geodetical monitoring equipment was installed in July 2011. After monitoring system was powered up and turned on, several problems in equipment functioning were observed and equipment readjustment was carried out until the end of November 2011. Observations from geodetic prisms with robotic total station and GPS system are collected and processed in the automated integrated monitoring system software. During the first 18 months of monitoring system operating, the equipment calibration, system improvement and maintenance took considerable part of the system establishment. Seasonal meteorological and atmospherical conditions significantly influenced on monitoring equipment and results. Extreme temperatures during late June and whole July 2012 influenced in uneven bending deformation of the main pillar which affected on total station position and leaning and, consequently, on its measurements. While solar panel system power supplies at the landslide are sufficient for GPS rovers, the hybrid power system consisted of 1 KW solar panels and 500 W windmill located at the Veli Vrh location, during the late autumn and winter is not able to efficiently produce enough electric energy for main monitoring station consisted of PC workstation, robotic total station, main GPS unit, web camera and wireless network system to work continuously. However, collected measurement data are sufficient for observing the landslide in whole period, because of their consistent data trends and correlation between different data sets. In this paper the problems related to the installation and working of the system are described, as well as solutions those should improve the system for successful continuous work. Keywords landslide, monitoring system, calibration, maintenance Introduction The Grohovo Landslide, the largest active landslide along the Croatian part of the Adriatic coast, is located on the north-eastern slope of the Rječina River Valley outside of the City of Rijeka. It was noted that during 19 th and 20 th centuries considerable instabilities on the Rječina Valley slopes occurred. The last complex retrogressive reactivated landslide was activated in December 1996, after long dormant period and about 3.0x10 6 m 3 moved down the slope and buried the Rječina river-bed (Benac et al. 2005) (Fig.1). Figure 1 Aerial view at the Grohovo Landslide, May 2011.