DOPAS comprised an extensive European-wide project in which the Faculty of Civil Engineering of the Czech Technical University, ÚJV Řež, a.s. and SÚRAO participated on behalf of the Czech Republic. The aim of the Czech participation in the project concerned the construction of an experimental pressure and sealing plug (EPSP) in the granite rock mass of the Josef gallery. Sealing plugs will serve to separate the filled and unfilled disposal spaces in the future Czech DGR. The EPSP experiment was constructed in the middle of 2015. The construction of the plug itself confirmed that the technologies and materials used are suitable for application in the future DGR. The construction of the plug was accompanied by the installation of the monitoring system – approximately 250 sensors were installed in the experiment and the surrounding rock.
In order to verify the functioning of the plug, it was necessary to conduct the experiment over a relatively long period; hence the testing of the EPSP continued after the end of the DOPAS project. The experimental activities related to the pressurisation of the plug with water (at a constant pressure of approx. 1.25 MPa) included general monitoring and the monitoring and analysis of the outflows. Moreover, the monitoring process included the recording of the parameters of the structure of the plug itself and the surrounding rock mass every 10 minutes. The flow rate from the filters was measured both electronically and manually. Samples were taken from the outflows for basic chemical analysis.
The monitoring results indicated the gradual development of the saturation of the sealing part of the experiment with a simultaneous gradual increase in the swelling pressure; the outflows from the experiment decreased until stabilisation was attained. The progress of the experiment to date suggests that the plug is fulfilling its intended function. The concrete component acts to retard the flow and prevents the erosion of the bentonite. As bentonite saturation progresses, the bentonite core takes over the main sealing function; this process is long-term.