engleski

Introduction of one of Methods to Predict Failure Time of a slope widely used in Japan and application to the Kostanjek Landslide

This paper introduces one of the methods to predict failure time of a slope which has been widely used in Japan. Creep deformation of substance is generally described as that it proceeds through three processes (transitional creep, steady creep, and accelerated creep) and finally reaches failure. Slope failure can be also considered that it may follow the same process. Remaining time until slope failure has strong correlation with accumulated deformation semi-logarithmically. In this paper the method to predict failure time of a slope is explained using the actual data of the extensometer. An alarm system is one of the functions of the early warning system. However, when the early warning system is discussed, some time an alarm system tends to be set aside for issuing, because an alarm system may involve societies and become a social scientific aspect. In the last chapter the general design of the planned integrated monitoring system of the Kostanjek landslide (the city of Zagreb) will be briefly presented. A comprehensive integrated real-time monitoring system will be installed on the Kostanjek Landslide as a part of the research activities in the Croatian–Japanese Bilateral Project. The monitoring system will consist of 36 sensors for geodetic and geotechnical monitoring of landslide movement and monitoring of landslide causal factors. Equipment for monitoring of landslide movement at the surface and in the underground will include: 15 precise GNSS referent stations (GPS), 8 long-span extensometers and 1 vertical inclinometer. Pore pressure gauges in boreholes (3 pieces), water level gauges in wells (3 pieces), sensor for discharge measurement, rain gauge and accelerometers (4 pieces) are aimed at monitoring of landslide triggering factors. GNSS referent stations will be placed on 15 locations at the surface of landslide body with average distance between locations of 200-300 m (total landslide area is 1.2 km2). Extensometers will be installed at the top of the landside and at a left flank of landslide. Piezometers, inclinometers and vertical extensometers will be installed at one location in the central part of the landslide body. All monitoring equipment will be connected in one system with continuous monitoring and export of the data to a data center. An early warning system for possible landslide movement, which presents landslide risk for houses and structures, will be established, based on the monitoring results. Installation of the extensometers started in November 2011 and it will be finished until spring 2012. Installation of other components of monitoring equipment will start in spring 2012 and it is planned to be finished until September 2012. Because of the poor data, the existing landslide model is relatively rough. Establishment of the threshold values for early warning system requires additional reinterpretation of the landslide model in order to establish relationship between landslide hazard (velocity and magnitude of landslide displacement) and landslide risk (rate of damaging of endangered houses and acceptable risk). The described methods to predict failure time of a slope widely used in Japan will be applied to the Kostanjek landslide using data from installed extensometers, water level gauges and rain gauges at the top of the landside and at the left flank of the landslide. Collected data from early stages of monitoring together with historical data about landslide movements will enable estimation of possible application of proposed method to the Kostanjek landslide and possibility to develop an alarm system which will be used by OEM - City Office of emergency management.

Prediction method; creep deformation; extensometer; early warning system; alarm system

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