DEEP REPOSITORY R&D FOR RADIOACTIVE WASTE | ROCK TUNNELS
Top, figure 16: Core final state in terms of swelling pressure and dry density
Bottom, figure 17: Vertical contact stress at the plug-lining interface
period, the total radial stress increases following the rise of the water pressure back to its far-field value, while the effective radial stress slightly decreases to adapt to the small deformations that develop in the host rock and compressible material during the final hydro- mechanical equilibrium. Finally, it can be noted that, despite the
deconfinement and the general reduction of dry density, the central part of the core maintains a swelling pressure which can be considered within the admissible design range. The response and general performance of the
expansive core can be summarised in Figure 16 by plotting the final swelling pressure against the final dry density at core points C1a, C2a, and C3a. The reduction of density and swelling capacity clearly affects the whole core and increases progressively from the central part to the end close to the concrete plugs. An interesting aspect is that the relationship between mean swelling pressure and dry density follows the Bernachy-Barbe et al. (2020) fitting curve, as the wetting process is monotonic in both the laboratory tests and the simulation. From a simplified point of view, stress development
within the core can be viewed as controlled by: ● Longitudinal stress dissipation by friction at core perimeter during concrete plug sliding;
● Longitudinal swelling pressure decrease due to progressive loss of constant volume condition, dependant on volumetric deformation imposed by concrete plug displacement and on the material density–swelling pressure relationship; and,
● Radial swelling pressure decrease due to the longitudinal and mean swelling pressure decrease. The radial stress controls, in turn, the friction at core perimeter.
System Equilibrium and Plug-Lining Interface The longitudinal displacements shown in Figure 14 provide information about the performance of the concrete plugs and backfill material to support the pressure exerted by the sealing core. The maximum longitudinal displacement obtained at the end of the core in contact with the plugs (z=10m) is around 0.5m. The shear strength of the interfaces between
supporting elements and lining (i.e., concrete–concrete interface and backfill–concrete interface) and the reaction of the backfill (governed by the stiffness and strength of the material) are the principal mechanisms contributing to the final equilibrium. Total shear
time = 10000 years 00.15 0.30 time = 100 years
Vertical stress at plug-lining interface [MPa]
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Backfill
LP2 Core
LP1
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