Abstract Geochemical investigations of sediments from core GC22 from the Tonkin Gulf, South China Sea, have been carried out in order to reconstruct the palaeoenvironmental evolution of the area during the Holocene. Vertical variations in Al/Ti, K/Al and Mg/Al clearly indicate the degree of chemical weathering in the source area. Zr/Ti and SiO 2 /Al 2 O 3 recorded the history of current velocity changes, and La/Co v. La/Sc, combined with distribution patterns of rare earth elements, suggested that Hainan Island was the main source of the sediments during the Holocene. Based on the results of the analysis, the evolution of palaeoenvironments in the Tonkin Gulf can be divided into four stages: (1) 10.12–6.46 ka BP, the regional climate got warmer, and the sea level of the gulf rose rapidly, which is indicated by rapid declines in Sr/Ba and CaO. (2) 6.46–4.3 ka BP, the gulf had a stable depositional environment, and the local climate became cold and dry. (3) 4.3–3.55 ka BP, the currents and sedimenary provenance in the gulf were significantly influenced by the opening of the Qiongzhou Strait. (4) 3.55 ka BP–present, the regional sea level remained roughly stable.

Abstract The excavation damaged zone (EDZ) around a radioactive waste repository will act as a potential escape route for gases produced from anoxic corrosion of waste containers and other metallic components within the underground facility. For assessment of the impact of the gases on the repository safety, the gas-flow behaviour of the EDZ has to be characterized, understood and predicted. This issue has been recently investigated for the Callovo-Oxfordian and Opalinus claystones at the GRS laboratory. Various kinds of gas-flow experiments were carried out by flushing nitrogen gas through cracked and resealed claystone samples under different hydromechanical conditions. Extensive results obtained include: (a) gas permeability of fractured claystones in relation to fracture closure under loads; (b) effects of gas humidity on the sealing and gas permeability of fractures; (c) gas-flow behaviour in water-saturated and resealed fractures characterized by three key parameters, namely gas-breakthrough pressure, permeability and shut-in pressure; (d) relationships of the gas parameters to the intrinsic permeability of the resealed claystone and the applied confining stress, as well as relationships between the gas parameters; and (e) the impact of gas-pressure rise on the reopening of the closed pathways and/or creation of new ones in resealed claystone.

Abstract Crushed claystone produced by excavation of repository openings has been investigated as backfill/seal material. The raw coarse-grained claystone can be used for backfilling repository openings and, in mixture with bentonite, for sealing boreholes, drifts and shafts. The investigation programme focused on characterizing the thermo-hydro-mechanical properties of the excavated Callovo-Oxfordian claystone and the compacted claystone–bentonite mixtures, including (1) mechanical compaction, (2) gas and water permeability as a function of porosity, (3) water retention and saturation, (4) swelling capacity and (5) thermal properties of the materials. The major results are presented in this paper.