The selection and the design of rockfall protection works often relies on the evaluation of the energy involved in the possible phenomena. This requires the identification of a characteristic energy value: this is usually done through numerical simulations of block trajectories, both in 2D and 3D, from which the actual reference value of total kinetic energy at a specific location along the slope can be identified. The experience and expertise of the designers play a crucial role in the choice of the input parameters: the process heavily depends on the choices of the reference values themselves, making the approach highly deterministic and often empirical. A possible alternative design approach would rely on the probabilistic description of the phenomenon, through the use of distributions of the most relevant parameters, instead of deterministic values. The method proposed here is based on the identification of the characteristic In situ Block Size Distribution (IBSD) of a rock mass identified as rockfall source area, and 2D numerical simulations of block paths. From a significant number of these simulations, the probability distribution of the design parameters is obtained: in the case of passive protection works, such as flexible barriers or embankments, this corresponds to the definition of the Total Kinetic Energy probability distribution, which can support the identification of the energy level the structure is required to withstand, and to the Bounces Height probability distribution, which can direct the choice of the height of the structure. The significant advantage of this probabilistic approach lies in two key features. The first one is the rigorous statistical treatment of the parameters involved, as required for the definition of the IBSD: this provides in return a significantly reliable method, devoid of empirically based choices, yet simple and quantitative. It is also important to note that the probability distributions of the design parameters can still be used in a traditional design approach to quantitively justify the choice of characteristic values. On the other hand, describing the phenomenon in a probabilistic way also allows for methods based on failure probability to be employed. The second advantage is the possibility to define generalized acceptable levels of residual probability, through which standardize the selection of the design parameters. In this way, the designers, who assume a significant responsibility when dealing with these choices, could be provided with a tool to deal with possible predictable consequences.

This paper presents a methodology to identify key blocks in highly structured rock masses. Calculating the stability of these key blocks is critical to forecasting geotechnical risk in terms of potential failure volume and runout distance. Key blocks are determined using structural mapping data from photogrammetry data acquired by drone flyovers. The Factor of Safety of key blocks is then calculated using limit equilibrium methods. Any key block with a Factor of Safety less than one is then systematically removed from the slope to determine the maximum potential volume of slope unravelling once the key block is removed. This information is then used to determine potential runout distances. Sections of slope predicted susceptible to failure (i.e. Factor of Safety less than one) can be the focus of proactive monitoring or hazard control (e.g. through the forward instalment of barriers, exclusion zones, etc.).

The problems of collapse sinkholes (simas) that have affected the population of Alcalá de Ebro are very old. Since 1980, both the SGOP and the CEDEX, among others, have worked on the investigation of an area located at the entrance of the Population where there have been several subsidences (collapses), affecting a street, the flood defense area of the Ebro River, and some houses. Since then, different recognition techniques have been applied with the intention of assessing the geological-geotechnical model of the affected environment. All the information obtained in previous studies was reviewed and expanded, to improve correlation and the scheme of the internal structure of the subsoil was completed by means of a geophysical profile based on techniques: Cross-hole and MASH. The resulting profile after incorporating all the data obtained in the different research reports carried out/compiled, allows an interpretative model to be reached and the following conclusion to be obtained: The basis of the problem that facilitate the generation of sinkholes-chasms at this point in Alcalá de Ebro is located at a level or stratum, from 4 to 6 meters in relative thickness, located at a depth of between about 14 (from the access street to Alcalá), which is formed by an alternation of highly soluble rocks: massive gypsum ( usually in the form of nodules), glauberite, and possibly thenardites and epsomites. The most relevant thing is that levels or layers of salt (halite) have also been recognized. The apparently affected surface made it possible to evaluate consolidation solutions that were initially based on injections of expansive resins and later on injections of low mobility mortar. The latter were carried out in two phases during the years 2017 and 2018. The aforementioned “mortar columns” descended between 21 and 23 meters until they crossed the affected area and entered firm ground. Once the treatment with mortar was carried out, the embankment was reinforced, on the surface, using flexible geogrids, but with high tensile strength. At present (almost 5 years after carrying out the consolidation works), the results have been monitored, carrying out high-precision level and measurements with terrestrial laser-scanners. Geophysical research work continues to be carried out using Ultra GPR georadar and electrical tomography. The apparent results obtained are positive and allow evaluating a technique of consolidation and improvement of the terrain, in a particularly sensitive point affected by frequent subsidence and collapse processes.

Coal mining in the eastern part of Saar district (Germany) caused numerous seismic events. After a ML = 4.0 event (93.7 mm/s PPV) in 2008 mining was stopped for good. Coal has been extracted by the longwall mining method at depth below surface of 1600 m. During extraction the mine water was kept below the deepest seam by pumping at central shaft. In 2013, the pumps were shut down and the water level in the shaft rose. Seismic events occurred immediately and the water level in the shaft was kept from 2015 on constant at 300 m higher compared to the level during mining. Two cluster of mine-water induced seismic events were observed. One cluster is located around the panels in the area where seismic events occurred during mining, which is no surprise. Another cluster is in the undisturbed rock mass away from longwall operations, i.e., in an area of approximately 6 km² surrounded by separate fields of panels. The only conduits for water in that otherwise undisturbed area/ volume are several 6 m x 5 m gateways directly connected to a shaft outside that area. Major faults are present there and the mining authorities wanted to know whether seismic events may occur with further rise of mine water in the shaft. This paper describes the methodology for arriving at estimates of future seismic events caused by elevated pressure from mine flooding. Substantial numerical modelling was necessary for estimating the spatial water pressure distribution over time. Fault planes from focal analyses were compared with known discontinuity orientations at different scales. Finally, based on the concept of the mobilized friction angle of discontinuities, it was concluded that the major faults will not contribute to the seismic events during further rise of mine water.