For the description of the compaction behavior of crushed rock salt for use as a backfill material in underground radioactive waste repositories, a constitutive model is proposed based upon phenomenological and theoretical considerations and experimental results. It can be shown that the constitutive model describes very well the experimental results of different authors within the nearly full extent of compaction.
pour la description du comportement de la compaction de sel broye pour s ' en servir de materiel de remblayage dans des depôts souterrains de dechets radioactifs, un modèle constitutif est propose qui se base sur les aspects phenomenologiques et theoriques ainsi que des resultats experimentaux. I1 peut être montre que ce modèle constitutif decrit tres bien les resultats experimentaux de differents auteurs dans presque toute la rangee de compaction.
zur Beschreibung des Kompaktionsverhaltens von Salzgrus als Versatzmaterial in unterirdischem Endlager radioaktiver Abfalle ist ein Stoffansatz auf der Basis phanomenologischer und theoretischer Aspekte und der versuchsergebnisse aufgestellt. Es zeigt sich, daβ dieser Stoffansatz die versuchsergebnisse verschiedener Autoren fast in vollstandigem Bereich der Kompaktion sehr gut beschreibt.
Crushed rock salt is a candidate material for use as a backfill material around the waste packages in storage rooms, in shafts and other underground openings during and after the operational phase. It is expected that in response to the creep closure of the mine openings the crushed rock salt will be recompacted sufficiently to serve as an efficient component in the seal systems. So the mechanical behavior of crushed salt is of interest for the long-term assessment of the sealing performance in underground radioactive waste repositories. In recent years, theoretical and experimental investigations on the compaction behavior of crushed salt have been conducted. Many efforts focused on the development of realistic models capable of predicting the long-term compaction of crushed salt as a function of pressure, temperature, and time or loading rate [DIEKMANNet al., 1989 and 1991; FORDHAM,1988; HOLCOMB et al., 1982 and 1988; KAPPEI, 1987; LIEDTKE et al., 1985; SJAARDEMA et al., 1987; SPIERS et al., 1989; YOST et al., 1987; ZEUCH, 1989; ZEUCH et al., 1991; ZHANG et al., 1992]. In this paper, a constitutive model based upon both phenomenological and theoretical considerations and experimental results is presented. Laboratory tests were performed in order to verify the constitutive model and to provide parameters for the calibration of the model.
The compaction behavior of crushed salt results from a number of different mechanisms. Which mechanism is dominant depends on the pressure, temperature, material properties and particularly the moisture in the crushed salt backfill. From the researches of FORDHAM, (1988), HOLCOMB et al. (1982 and 1988), SJAARDEMA et al. (1987), SPIERS et al. (1989), YOST et al. (1987), ZEUCH (1989) and ZEUCH et al, (1991), it is known that at higher stresses, grain re-orientation, grain breakage, intergranular gliding and intragranular dislocation glide are controlling mechanisms for dry crushed salt. Under the anticipated repository conditions, namely at lower convergence rates of the mine openings, temperatures from ambient to 200°C and possibly in the presence of brine or moisture, compaction of the material is governed by the combined mechanisms of intergranular gliding and intragranular dislocation glide, pressure solution, grain growth and recrystallization. The knowledge of microstructural deformation mechanisms should be the best basis for the description and extrapolation of the compaction of crushed salt down to very low porosities. But each of these mechanisms can be expected to lead to a different constitutive model. However, many constitutive models which are based upon only one or two micromechanical mechanisms have considerable imperfections because they are severely restricted by the used physical equations.