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Full-scale test of the Dome Plug for KBS-3V deposition tunnels. Project summary and evaluation of the final results
Sweco.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.ORCID iD: 0000-0003-3586-8988
2019 (English)Report (Refereed)
Abstract [en]

This is the final project report that summarizes the dome plug full-scale test (DomPlu) intended to evaluate the design concept of the deposition tunnel end plugs for the KBS-3V reference disposal system. The DomPlu full-scale test, was carried out at the Äspö Hard Rock Laboratory (Äspö HRL) and tested the plug system in a realistic environment with realistic and excessive loads. The current SKB reference design and the DomPlu design for a deposition tunnel end plugs are similar, except for a few experimentally related modifications. The DomPlu therefore represents a more detailed iteration of the basic design rather than a fundamental change to the earlier plug experiments undertaken by SKB. In this project, the behaviour of the plug has been evaluated when subjected to a constant water pressure load of 4 MPa for three years. After this, a gas tightness test was performed to evaluate the gas tightness of the plug. The last test was a strength test intended to test the load carrying capacity of the concrete dome during high pressure loads. Finally, the dome plug was demolished, and the included systems and materials were evaluated. To evaluate the dome plug, monitoring has been performed since construction where about 100 sensors were installed in the different material zones in the dome plug. Besides this, other types of measurements have also been conducted such as; leakage measurements, non-destructive test methods and a large amount of material tests on concrete and bentonite. As a complement to all these measurements, numerical analyses have also been performed to predict and to obtain greater understanding of the results. During the gas leakage test, the filter of the plug was drained to remove the water. After this, the filter was filled with helium and the gas pressure was continually recorded and a sniffer was used to track leakage downstream of the plug. The results from this test showed that the plug can be considered to satisfy the requirements of gas tightness. In the strength test, the water pressure was temporarily increased to 8.1 MPa, resulting in a total pressure about 10 MPa. The results showed that the concrete dome behaved as expected and some nonlinear deformations occurred. The deformations did not, however, result in significant cracking or damages within the concrete dome. The measurements of the leak tightness of the plug showed that the leakage varied between one and two litres per hour (17–33 ml/min). This should be considered as an upper limit of the expected leakage of the DomPlu design, since the natural pressure from the groundwater was lower than the artificial pressure applied in this full-scale test. In addition, the results showed that leakage to a great extent by-passed the bentonite seal through fractures in the rock. Therefore, it is of great importance to choose a plug location with limited fractures. The swelling pressure in the bentonite seal was lower than expected and varied between 0.2 and 1.9 MPa. The results also showed that the water content in the central parts was lower than expected. This has likely been a result of the leakage by-passing the seal in the rock. During demolition, great experience was obtained from material test sampling of concrete and bentonite. A larger waterfilled cavity was also detected in the top of the concrete dome, which had not been seen with the non-destructive test methods. Overall, the DomPlu full-scale test has showed that the plug design is robust and could sustain high water pressures and obtain quite low rates of leakage despite the fractures in the rock and the cavity in the top of the concrete dome. The full-scale test has also showed that it is possible to build and (if necessary) breach and demolish a plug.

Place, publisher, year, edition, pages
2019. , p. 116
Series
SKB TR18-02
Keywords [en]
Dome plug, Deposition tunnel end plug, Pressure test, Gas tightness test, Bentonite seal, Backfill transition zone, Filter, Gravel, Concrete dome, B200, KBP1016, DOMPLU
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering, Concrete Structures
Identifiers
URN: urn:nbn:se:kth:diva-261152OAI: oai:DiVA.org:kth-261152DiVA, id: diva2:1356701
Available from: 2019-10-02 Created: 2019-10-02 Last updated: 2019-10-02

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