Research Projects

Project 1: Interim storage of wind power by using underground pump storage stations in closed mines - geomechanical aspects

project executing organisation: Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)

project number: FKZ 0325074

project period: Oct 2010 - Mar 2012

Windenergiespeicherung

Windenergiespeicherung2

The goal of the project is to analyze the possibility of an interim storage of wind power by using underground pump storage stations in old mining areas. From the geomechanical point of view the feasibility of the foresaid idea depends on the static stability of the underground openings which must be excavated to store the water in an upper and lower basin, to connect the basins by a pressure shaft, to install the turbine and generator in an underground cavern and to guaranty the infrastructure for the all over operation by mine drifts. The static stability of underground openings depends on rock and rock mass strength, geology, tectonic elements, stress-strain and hydraulically behaviour of rock and rock mass, the primary stress field, the depth of the underground openings, the distance of excavations to old mining areas, the excavation method and last but not least the reinforcement. Taken into account the foresaid bearing values geomechanical calculations based on empirical, analytical and numerical computations are done for an underground storage system which is characterized by parallel drifts with a cross section area of about 30 square meters. Because only few respectively no informations regarding the geomechanical behaviour of the site specific rock mass are available, the calculation is defined by a very row estimation. Nevertheless it was estimated, that there are no basements which answer back the assessment, that the basic feasibility of the project is given. Regarding to the quality and amount of reinforcement needed to guaranty the static stability further investigations of the site specific situation are heavily demanded.

Project 2: Comparison of current constitutive models and procedures based on model calculations for the thermo mechanical behaviour and healing of rock salt

project executing organisation: Federal Ministry of Economics and Technology (BMWi)

project number: 02E10820

Flac3d

Flac3d


This joint project is a collaboration of several project partners with the aim to review and improve tools used for the proof of safety concerning the long-term underground disposal of heat-generating high-level radioactive waste in rock salt formations. This includes constitutive models to describe the thermal-mechanical-hydraulic coupled behaviour of rock salt. The project follows the two BMBF joint projects "Modelling of the mechanical behaviour of rock salt: Comparison of current constitutive models and procedures" (01.04.2004 to 30.11.2006) and "Comparison of current constitutive models and approaches based on 3D model calculations for long-term mechanical behaviour of real underground structures in rock salt "(01.08.2007 to 31.07.2010). In this project, founded by the German Federal Ministry of Economics and Technology (BMWi), the different modelling approaches developed by the project partners to describe the thermo mechanical behaviour of rock salt as well as its healing-ability should be analyzed. Therefore, each project partner performs coupled thermo mechanical 3D benchmark simulations with his constitutive model regarding stress, deformation, dilatancy and damage evolution and healing-effects in two real underground structures in the Asse II salt mine. The simulation results are compared with each other and with measured data. Thereby, an assessment of the capability of the different constitutive models can be given for the disposal of heat- generating radioactive waste in rock salt formations. In the Project numerous specific laboratory tests are carried out for the determination of salt-type-specific parameters as well as the verification of the constitutive models for the thermo mechanical behaviour and healing-effects in rock salt. The Chair of Waste Disposal and Geomechanics participates in this BMWi joint project with its self-developed constitutive model Lux/Wolters and performs healing-tests on rock salt specimens in its rock mechanical laboratory

Project 3: Dynamic of drown or flooded salt mines and their Caprock - geomechanical modelling

project executing organisation: Federal Ministry of Education and Research (BMBF)

project number: 02C1486

Flac3d

Flac3d


The Staßfurt location is characterized by surface subsidence and caves to the surface (sinkholes) due to collapse and drown of potash mines in the past. Solution of rock salt and potash occurs over decades of years, induced by fresh water circulation through the drown salt deposit and generates continuing surface subsidence and sinkholes. In order to predict surface development in the future geomechanical calculation based on numerical methods are done. Basic demands for a sufficient calculation of future surface subsidence are the acknowledgment of the geologic underground structure, the material behaviour of the rock mass, the geometry of underground excavations, a time schedule of mining operation events such as excavation, collapse, flooding, caves to surface, etc. and last but not least applicable criteria to decide weather or not the load bearing behaviour is leading in a rupture of rock mass. Taken into account the foresaid demands a geomechanical calculation model could be prepared and based on sensitivity studies a numerical recalculation of the measured surface subsidence could be done. Additionally to the numerical recalculation of the measured surface subsidence induced by convergence processes as well as failure processes in an old mining area it could be shown, that geomechanical calculations are applicable to verify the given data of the geological and tectonic structure as ell as the mining situation concerning the volume of underground openings caused by excavation or leaching.

Project 4: Options for surface-based surveys to assess repository sites in argillaceous formations

project executing organisation: Federal Office for Radiation Protection (BfS)

project number: UFOPLAN-Vorhaben 3607R02596

Bohrloch


The question has been raised as to whether restricting a survey to laboratory investigations on specimens and borehole observations, in particular for sites having sedimentary geosystems such as argillaceous rocks, allows a safety-relevant and reliable estimate of site properties both in terms of a comparison of argillaceous formations with one another as well as for com-parison with sites in saliniferous geosystems. Within the terms of this research project and against this background, consideration is given to four key issues:

  1. What influence do anisotropic primary rock mass stress states, rock anisotropy and joint-ing have on the load-bearing behaviour of underground openings in an argillaceous rock mass?
  2. Can the load-bearing behaviour of boreholes be considered as sufficiently representative for the load-bearing behaviour of drifts and emplacement chambers, and which limita-tions exist?
  3. Can the load-bearing behaviour of argillaceous rock mass be technically measured in boreholes, which fundamental phenomena are observed and can statements on spatial and time-dependent load-bearing behaviour be concluded?
  4. How should a surface-based survey programme be structured from a geomechanical viewpoint in order to draw meaningful and reliable conclusions for a comparison of sites including sites in argillaceous rock mass?

These questions are reflected within the concluding report initially by way of the results of numerical investigations into the effects of the bedding plane structure as is always present in sedimentary rocks, such as claystones. The final report also presents:the observation results of a two-year borehole observation campaign in the underground laboratory at Mont Terri near St. Ursanne (Switzerland). The key aspect here is the geomechanical influence of pore water.

Project 5: Validation of modelling approaches for claystone rock mass by means of in situ-experiments performed at the Tournemire Underground Rock Laboratory (France)

project executing organisation: Federal Ministry of Economics and Technology (BMWi)

project number: 02E10427

Tournemire

Research project 02E10427 was elaborated with the aim of further developing the less exten-sive information about characteristics and load-bearing behaviour of argillaceous rocks in comparison to rock salt, looking in particular at the consolidated argillaceous rocks at the Tournemire location?focusing on physical modelling and numerical simulation, as well as on field and laboratory investigations. The main findings from the different aspects looked at during this research project can be summarised as follows:

  • Concerning physical modelling, the strain-based combined failure and dilatancy criterion formulated in this report yields a first plausible approach to an explanation of the time-dependent development of the observed softening phenomena in the Tournemire drift sys-tem.
  • Sets of own model parameters based on own mechanical laboratory investigations of Tournemire claystone material could successfully be derived.
  • The usage of borehole observation equipment developed within this project (calliper probe, borehole camera, and humidity sensors) provided extensive insights into the load-bearing behaviour of the claystone rock masses at the URL locations Tournemire and Mont Terri.

Project 6: Coupling of the softwarecodes FLAC3D and Tough2 in combination with in situ-, labo-ratory and numerical investigations regarding the thermo-hydro-mechanically coupled behaviour of claystone rock mass

project executing organisation: BFederal Ministry of Economics and Technology (BMWi)

project number: 02E11041

Bohrloch

Research project 02E11041 is currently conducted. It's main aim is the development of a new simulation tool for the thermo-hydro-mechanical analysis of rock-mass behaviour by combin-ing the software FLAC3D and the software Tough2. In addition to the software development field investigations at the Tournemire Site (FR) and the URL Mont Terri (CH) are performed as well as laboratory investigations.

Project 7: Risk assessment for the longer term maintenance of Asse

project executing organisation: Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)

Asse

The Institute of Waste Disposal and Geomechanics of Technical University of Clausthal was assigned by the Institute for Applied Ecology Darmstadt to perform rock mechanical investigations within the project "Risk assessment for the longer term maintenance of Asse" in response to a request from the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU). The objective of the interdisciplinary project is the investigation of possible consequences of the longer term (dry) maintenance of Asse II. In case of a flooding mining safety and radiation protection issues have to be taken into account. Especially the scenario of a flooding that might occur faster than the recovery of the waste from the ASSE II mine can be performed is investigated.

Project 8: Further development of the EDV-software INFIL for numerical simulation of pressure-driven infiltration processes of fluids into a non-permeable barrier rock mass (rock salt)

project executing organisation: Federal Ministry of Education and Research (BMBF)

project number: 02C1355

P8

The process of pressure-driven fluid infiltration can adversely affect the load-bearing behaviour and the long-term integrity of the geological barrier in the near-field of closed underground cavities. Therefore, a sufficient understanding of the process of pressure-driven fluid infiltration as well as the development of approaches for physical modelling of the infiltration process and the development of software for its numerical simulation is of great importance in assessing the long-term safety of underground repositories for hazardous or radioactive. The aim of the BMBF-funded research project "Further development of the EDV-software INFIL for numerical simulation of pressure-driven infiltration processes of fluids into a non-permeable barrier rock mass (rock salt)" has been the further development of the computer software INFIL for numerical simulation of the pressure-driven fluid infiltration process into a primarily impermeable salt rock mass. As a basis for physical modelling as well as numerical simulation of this process, extensive laboratory studies concerning this process have been performed. In addition, the numerical software has been modified to enable the simulation of 3D-situations. This project has been successfully completed by the creation of a final report in December 2009. Based on the results of this project, afterwards the numerical software has been further improved. It is now used in the context of third-party projects related to practice.

Project 9: Disposal options for radioactive residues: Interdisciplinary analyses and development of evaluation principles

project executing organisation: Federal Ministry of Education and Research (BMBF)

project number: 02S9082A

In Germany, the disposal of radioactive, in particular heat-generating waste has become a complex issue that cannot be solved in a pure technical and scientific way. Not only the variety of possible disposal options and variants, but also the resultant social, legal and ethical aspects necessitate the need for a comprehensive, interdisciplinary embossed multi-criteria evaluation. This project has the aim of forming a research platform for the promotion of scientific exchange and interdisciplinary collaboration between natural scientists, engineers, humanist, jurists and social scientists dealing with the disposal of radioactive waste materials to perform scientific research as well as to disciplinarily and interdisciplinarily educate and train young scientists. The Chair in Waste Disposal and Geomechanics engaged in this project with the numerical THM-coupled near-field process simulation in salt rock mass as well as in clay stone rock mass and with the development of a concept for in-situ data collection and demonstration of safety-relevant phenomena in the monitoring phase of a repository.

Project 10: Some geomechanical aspects of compressed air energy storage (CAES) in salt caverns

project executing organisation: Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU)

project number: 0327628

Grundlast

The paper deals with some geomechanical aspects of compressed air energy storage in salt caverns. One main aim of the paper is to analyse weather it is technically and economically feasible to store and restore wind power in salt caverns. Because the availability of wind is time dependent whereas the need of electric power is continuous, an intermediate storage of wind power is required. The intermediate storage of wind power basically could be done by compressing air in times with more wind power than needed for the grid and decompressing air in times with less wind power than needed for the grid. The compressed air itself potentially could be stored in salt caverns. From the geomechanical point of view this simple idea causes some problems regarding to the cavern stability. In comparison to the well known geomechanical design of natural gas storage cavities four significant differences between gas and compressed air storage in salt caverns must be pointed out:

  1. The cyclic turnover between fluid injection and withdrawal for compressed air energy storage is a multiple of that used by natural gas storage.
  2. The maximum cavern inside pressure for compressed air energy storage is limited by the allowable turbine input pressure which is in a level between 30 and 80 bar.
  3. Cyclic loading by compressed air energy storage requires to superimpose thermal induced and mechanical stresses.
  4. Compressed air energy storage is defined by the need of an ordinary operation phase with atmospheric cavern inside pressure.

To present the load bearing behaviour of CAES caverns the results of numerical investigations have been analysed taken into account the coupled thermo-mechanical calculations as well as the specific operation pattern of compressed air energy storage caverns. Special attention was given to thermal induced tensile stresses in the near field of the cavern contour and lab tests, necessary to estimate the consequences of thermal induced tensile stresses to the stability and tightness of the surrounding rock mass on the one hand and the creep behaviour of rock salt by cyclic loading on the other hand. A short summary of the project could be given by the following statement: From the geomechanical point of view a raw estimation about the load bearing behaviour is available by using design concepts learned from natural gas storage in salt caverns. To transfer the idea of compressed air energy storage into a save technical and economically optimized application, further investigations are needed to understand in detail the complex material behaviour of rock salt by cyclic mechanical and temperature loadings combined with multiple interactions to the operation pattern of CAES caverns.

 

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