Engineering geological clay research for a radioactive waste repository in Slovakia

摘要

Research for the deep geological repository (DGR) started in Slovakia in 1996. Results of the engineering geological research of the clay in both, the natural and engineered barriers are summarized in the paper. The Szécsény Schlier from the Lu?enec Formation is a potential sedimentary host rock for the DGR in Slovakia of favourable properties, similar to a natural clay barrier. It is a friable calcareous siltstone with intercalations of silty clay and fine-grained sandstone, of low hydraulic conductivity (k?10-10 m.s-1) and acceptable uniaxial compressible strength (from 18.5 to 34.8 MPa). Engineering geological characterisation of this formation is based upon rock samples collected from boreholes and tested in the laboratory. Several deposits in Slovakia might offer suitable buffer/backfill material for engineered barriers of the DGR. Since 2003 five bentonite types have been studied, selected results of the engineering geological evaluation are discussed in this paper. Liquid limit was the first suitability indicator. Grain fraction 0.250 mm was preferably used in the swelling tests, needing lower compaction pressures than finer fractions. Bentonite from Jel?ovy Potok deposit showed a very good quality of pressed high-density samples (with uniaxial compressive strengths similar to weak rocks) and the best swelling potential. Comparing physical and mechanical properties, succession Dolná VesLastovce?LieskovecKopernica?Jel?ovy Potok can be written. However, bentonite from Dolná Ves was considered as an alternative because of the very good compatibility and, particularly, large amounts available in the deposit.