Usage of Terrestrial Laser Scanners (TLS) is currently the best way of monitoring and detecting changes in slope morphology. In this study Optech ILRIS-3D was used. First scan of slope morphology with ILRIS-3D was made in March 2012 at presented pilot location "Znjan" and it was repeated in 6 month intervals to this day. Series of observations in man-made cuts at additional 14 pilot sites using TLS were also made. For the purpose of forecasting and retrograde analysis, the survey was conducted in different time intervals and number of observations. Main goal of this monitoring was to define the average rate of erosion in cuts in this type of material. Also, a proper procedure for establishing future monitoring in this type of materials is introduced, as well as guidelines for selecting minimum and maximum time intervals. Finally, based on the results of monitoring, known mathematical model for development of erosion in cuts is calibrated and the guidelines for its usage are proposed.
Marl from Eocene flysch strata, which can be found in Dalmatia region in Croatia, is just one example of soft rocks. Excavation in this type of materials could be performed only with the use of heavy machinery (rock breaker) or explosives. However, in a short time after excavation, in which the excavated cut in marl is exposed to influence of atmospheric agents, weathering process starts to affect material on the slope surface (Miscevic & Vlastelica 2012). Repeated cycles of wetting and drying, heating and cooling, freezing and thawing, as parts of weathering process, can cause deterioration of marl into soil-like material. As a result of weathering, surface formed of weaker marl is eroded, and harder components of flysch can "stick out" on the slope surface like "cantilevers" (Fig. 1). In time, blocks of sandstone start to fall off the cut, and weathered marl is prone to both surface and deep sliding (Vlastelica 2015). Therefore, a suitable method for predicting these events is needed.
Each new insight into the processes that cause the instability of slopes can help to mitigate the consequences thereof. The development of new technologies in the field of geodesy, primarily LiDAR (Light Detection and Ranging) technology, opens new paths for monitoring changes in the earth's crust and the material from which it was created. These changes can be monitored on a global level, but also at the local level using TLS.
LiDAR technology, combined with a variety of platforms (satellites, planes, helicopters, …) has developed into an indispensable tool for creating DEM models (Digital Elevation Model), and also for a range of applications in agriculture, archaeology, geology, mining, meteorology, etc. (NOAA 2012). With the development of portable variants, also known as TLS, which are more precise and within accessible price range, this technology found its application in monitoring the progress of erosion of slopes that were not available from aerial photographs (Lim et al. 2009, Dewez et al. 2009, Perroy et al. 2010). Figure 2 presents terrestrial laser scanner ILRIS-3D-ER used in this study.
