FIELD SITE IN GERMANY

Germany has been one of the largest coal producers in Europe for many years. It had many coal mines located in different regions. The post mining problems, specific to the project objectives revealed at the coal field Erkelenz, near the border with Netherlands. In this area, mining was carried out by Dutch and German operators. The hard-coal field of Aachen and South Limburg provide a cross-country deposit between Germany and the Netherlands (fig.10); this coalfield is an extensively spread hydraulic system. Only 10 km northeast from the Aachen mining region, there is the Erkelenz coalfield. The Aachen mining region was closed down in the 1990s. This region has faced several seismicity events in the past, which led to damages in some cities.  Ground uplifts, along a line of 9km length, had caused a number of damages to buildings in the towns of Wassenberg and Hückelhoven in the Erkelenz region.

For the South Limburg hard-coal area (the Netherlands) several cases of mining damage to residential buildings and a shopping centre in 2012 are reported. The types of damages can also be linked to ground movements of divergent directions. Moreover, the building damages lay in the range of documented terraces which corresponded with previous cumulated edges of mined areas

In the cases cited above, the damages were tied to large-scale tectonic structures or to mining edges where, during the mine water rebound, differences in ground uplifts did occur. Principally, however, the probability that unsteady ground movements will occur is to be assessed as rather low, according to current expert. Where those occur indeed, an increased risk of building damage has to be assumed.

To investigate the above described hazards, it is necessary to conduct interdisciplinary research in the field of seismology, geodesy, gravimetry, geotechnics and hydrogeology. The integrated surveys will allow the study of geodynamics of post-mining areas and drawing more conclusions. Both the back analysis of available measurement data should be taken into account, as well as the current measurements should be supplemented with this information. It is necessary to create a digital platform on which all data and metadata about post-mining areas will be placed. For this purpose, all data and metadata should be unified and brought into common formats and coordinate system, so that they can be compared against each other. Such a methodology will allow to create a digital platform of information useful for the development of knowledge based on all available experiences. On the web-platform will be possible to view and visualize mining, geological, seismological, gravity and geodetic data. For this purpose, it will be necessary to develop common formats for the integration on the data from distributed measurement devices. Each partner will have its own IT center and will be responsible for providing unified data from a specific branches of science. The platform will integrate data and scientific methods related to the seismicity induced by any kind of technological activity, within a virtual environment. The collected data will enable interdisciplinary research of post-mining areas. The service created and constantly updated will be a modern IT tool, meant to facilitate research into geodynamic phenomena.

The data and metadata from the platform will be taken as input data to hydro-mechanical numerical modelling using Flac 3D or Plaxis software to study mechanisms of seismicity. The geophysical modelling and seismic/geodetic/gravimetric data will be used to study geophysical mechanisms of seismic events and to study deploying of seismic wave field on the surface.

The data collected will help as well to manage the post-mining seismic hazard and risks. To better characterize the hazard, innovative approaches will be applied to processes recorded seismic. This will allow to better characterise processes at the origin of the observed post-mining seismicity, in particular the role of the fluid in triggering of the seismicity. For risk management, Ground Motions Equations will be especially defined to take into account the specifity of post-minig EQ, which occur usually at shallow depths. Shaking maps, considering site effects, will be as well calculated. A specific effort will be payed to characterize the consequences of induced seismicity and to characterize the different potential types and level of damage comparing to the natural seismicity on the considered post-mining area. A guideline will be elaborate to assess the risk associated to induced seismicity. The early warning system, that already exists to manage post-mining risks on Gardanne site, will be improved. For that, a prototype web-platform that stores hazard and risk related data will be developed, to be easily accessible and understandable for the operators and decision makers. This tool will allow for easy configuration of multi-parameters based early warning system.