ROCK TUNNELS | DEEP REPOSITORY R&D FOR RADIOACTIVE WASTE
Longtitudinal displacements [m]
show that the obtained plastic zone provides an
extension, shape and permeability distribution than can be favourably compared with field observations, setting conditions for an acceptable hydro-mechanical state at the beginning of the subsequent natural hydration phase.
time = 100 years time = 150 years
Natural Hydration Process and Seal Performance In Figures 13 & 14, the spatial distribution of degree of mean swelling pressure and longitudinal displacements in the core are presented for different times. For ease of viewing, the upper half of the model is hidden. Contours values correspond to time steps from t = 100 years (initial state, after sealing structure construction) to t = 10,000 years. In Figure 15, time evolution of core degree saturation,
time = 250years time = 500 years
dry density, and the radial and longitudinal component of swelling pressure are presented for six points within the core indicated in Figure. 6 - C1a,b; C2a,b; C3a,b - all contained in the plane “x–z” (y = 0 m). Time evolutions of saturation indicate that the
time = 1000 years 0 0.125 time = 10000 years 0.25 0.375 0.50
expansive core is progressively hydrated in the radial direction from the perimeter towards the centre, and are of concern to the kinetics of hydration and not total duration. All the points reach full saturation more or less at the same time, around 2000 years after seal
construction (dashed line labelled as “Sat. t ~ 2000 y” in Figure 15. From the observation of dry density time evolution,
the central part of the core increases during the initial hydration process, related to the core first hydrating and swelling close to the host rock, which results in a compression at core centre. As time and hydration proceeds, all the core shows a general reduction of dry density due to deconfinement resulting from movement of the concrete plugs (see longitudinal displacements in Figure 14). On the time evolution of swelling pressure (Figures 13 & 15), it increases towards a maximum value that is less than the target swelling pressure (4 MPa). The final values reached at the different points relate to dry densities obtained at each. Thus, at the core, the result of the final non-uniform distribution of core density is a non-uniform distribution of final swelling pressure. A second observation relies on the difference
between the radial and longitudinal components of swelling pressure, where it is noted that the latter is systematically lower than the former, due to displacement constraints: in the longitudinal direction, the swelling pressure is controlled by plugs sliding; in the radial direction, the displacement is almost totally restricted by the concrete lining, where not removed, and by the host rock in the deposition zone. Moreover, it can be noted that final hydro-mechanical
Top, figure 14: Core longitudinal displacement evolution
Above, figure 15: Time evolution of core degree saturation, dry density, and the radial and longitudinal component of swelling pressure
30 | February 2025
equilibrium with hydrostatic conditions and the supporting elements (plugs and backfills) is reached after an additional 1000-years after full saturation (i.e., a total of 3000 years after construction—dashed line labelled as “HM- Eq. ~ 3000 y” in Figure 15. During this
Plug
Core
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