Project: GEophysical MOnitoring of long-term changes of the rock characteristics in the areas endangered by Subsidence procesS

The reason for the occurrence of events of land surface sinking or subsidence (with the exception of slope deformations) is most frequently gradual degradation of the rock environment near subsurface cavities. Such deformations of land surface always pose considerable risks which may result in injuries or fatal accidents and damage to the buildings and communications. Land surface deformations are often the reason for defects and breakdowns of distribution systems. Particularly high risks are posed to gas and oil pipelines. At present, we are witnesses of constantly increasing areas with the risks of these sudden land surface deformations. Increasing extent of endangered areas and associated risks is particularly connected with the development of human activities under ground (continuing exploitation of mineral raw materials, construction of tunnels, underground power plants, repositories, etc.). The next risk factor is the fact that we increasingly use for the development of towns and infrastructure also areas where the risk of land surface deformation is known but other viewpoints (such as strategic location, price, etc.) prevail. _x000D__x000D_Artificial cavities arise in association with human activities (for example, mining activities), natural cavities most frequently occur in karst areas (caves). In the vicinity of the cavities (most often in their overlying layers), a „stressless zone“ (a so-called EDZ zone - segment below Trompeter zone) is given rise to. It is a part of the rock massif which is bypassed by stresses arisen through concentrating the rock overlaier weight into cavity sides. This zone is susceptible to rock block collapses and caving. If its stability is not sufficiently secured, a cavity through gradual rock blocks dropping out hollows towards the ground surface, which may result in an event of subsidence/collapse. Reducing stress in EDZ zone and potential cavity hollowing towards the ground surface is also shown in a change of the physical properties of the rock environment in the vicinity of a cavity. Bulk density of the rock massif is changing, seismic velocities are changing, etc. The geophysical monitoring of such changes might be a new tool for control of the stability and safety of a territory endangered by the events of subsidence. _x000D__x000D_The objective of the project is to prepare optimal methodology of the geophysical monitoring for areas endangered by land surface deformations and events of subsidence. The project would consist of 2 parts: _x000D__x000D_Part 1 – practical measurements conducted in selected typical localities, the establishment of a database. The localities concerned should be on the territories of the Czech Republic and Germany, approx. 2 localities affected by undermining (ores, industrial minerals – coal), approx. 2 localities in karst areas. The CO methods applicable for the monitoring are microgravimetry, detailed seismic (also in the option of the drilling tomography) and resistivity measurements resp. geological radar:_x000D_- gravimetry gives sensitive response to changes of bulk density of the rock massif in the vicinity of cavities which relate with a change of stress (the formation of joints and their opening) or with the hollowing of cavities towards ground surface. Available for the measurement is the most modern gravimeter SCINTREX CG5, showing excellent repeatability of measurements and high resolution._x000D_- seismic measurements document changes in the propagation of seismic waves or analysis of microseismic noise in the vicinity of the cavities in dependence on stress changes in the rock massif. In this way, increased stress zones in cavity sides to which the weight of overlying rocks is transferred and also EDZ zone of reduced stress in the cavity overlier can be observed. The seismic tomography will be used from the drill holes near cavity, using nondestructive source of seismic energy (sparker). _x000D_- geoelectric resistivity measurement in the form of resistivity tomography might be used to describe the extent of the disturbed rock massif. However, in interpretation of repeated measurements it is necessary to distinguish resistivity variations caused by climatic effects._x000D_- geological radar might be used to observe the deformations of the geological layers in the cavity overlier and the extent of the rock massif disturbance according to the fluctuation of dielectric constant. _x000D__x000D_Part 2 – the analysis of the conducted measurements and draft of the methodology of the monitoring and interpretation of the data. The methodology should include and describe the following activities:_x000D_retrieval of available information on the area in danger; basic geophysical investigation; preparation of a monitoring grid layout of profiles/survey lines and points (including stabilization of the monitoring grid elements); methodology of the monitoring measurements and of interpretation of the particular monitoring measurement stages; the modelling – prediction of land surface deformations. _x000D__x000D__x000D__x000D__x000D_

Acronym GEMOSS (Reference Number: 4250)
Duration 01/01/2009 - 31/12/2011
Project Topic The project will define an optimal methodology of the geophysical monitoring for areas endangered by land surface deformations and subsidence. It consists of 2 parts: practical measurements conducted in selected typical localities & establishment of a database and the methodology of interpretation.
Project Results
(after finalisation)
The project GEMOSS dealt with the design of comprehensive methodology of geophysical monitoring of the rock environment in areas at risk of ground surface collapses. The places concerned are those undermined in the past, karst areas and also locations where excavations for new underground structures are to be carried out. Sudden deformations of the ground surface representing ultimate response of the rock environment to the existence of cavities bring considerable risks. They may cause damage to infrastructure (buildings, historic town centers, line structures, utilities and pipelines) and they also may lead to health hazards. The CO project outputs are:_x000D__x000D_GEMOSS methodology (Annex 10 to eProject for 2011) _x000D_Registered Utility Model No. 23901 entitled: Device for the measurement of loosening of the rock massif in undermined areas (Annex 17 to eProject for 2011). _x000D__x000D_The project results were presented at expert conferences (for example, the international conference OVA´11 „New Knowledge and Measurements in Seismology, Engineering Geophysics and Geotechnics“ in Ostrava Poruba between 12 and 14 april 2011. The title of paper: Repeated Geophysical Measurements in Areas at Risk of Ground Surface Collapses - Project GEMOSS Results, Vojtech Beneš, Dušan Dostál) and in professional journals (for example, Beneš V.: Geophysical Investigation above Jeroným Mine, Exploration Geophysics, Remote Sensing and Environment (EGRSE ISSN 1803-1447), XVIII.1 (2011). _x000D_
Network Eurostars
Call Eurostars Cut-Off 1

Project partner

Number Name Role Country
2 G-IMPULS Praha spol. s r.o. Coordinator Czech Republic
2 Geotomographie GmbH Partner Germany