ROCK TUNNELS | DEEP REPOSITORY R&D FOR RADIOACTIVE WASTE


Backfill


Plug


Gap


Core


Plug


Gap


Right, figure 18: Conceptual scheme of plug movement and resulting contact stress


Rotation


Long disp.


SWELLING


Weight


Self


Contact stress Backfill preconsolidation stress [MPa]


Contact stress


Right, figure 19: Backfill preconsolidation stress


time = 10000 years 0.15 0.275 0.40 0.525 0.65


4.5 4


3.5 3


2.5 2


1.5 1


0.5 0


1250 1300 1350 Note: Results indicated for φint 1400 Dry density [Kg m-3 ] = 0 correspond to the simulation without plugs


Above, figure 20: Effect of plug-lining interface strength reduction on core performance Note: Results indicated for pint = 0 correspond to the simulation without plugs


32 | February 2025 1450 1500 1550 φint


C1a - σx C2a - σx C3a - σx


φint φint φint = 20̊ = 10̊ = 0̊ φint φint φint φint = 30̊ = 20̊ = 10̊ = 0̊ = 30̊


C1a - σx C2a - σx C3a - σx


Isochoric test


simulation


strength of the interfaces is controlled by the friction


angle and the normal stress existing at the contact. In Figure 17 contour values of vertical contact


Bernachy- Barbe et al. 2020


stress at the interface between the plug and the lining are presented for time steps t = 100 years (after the operational phase and just after sealing structure construction) and t = 10,000 years. For ease of viewing, the concrete plug is not shown in the figure. The movements of the plugs are schematically


drawn in Figure 18. Before swelling, the contact stress is given only by the self-weight of the materials: it is high at the bottom and low or even null (gap formation) at the top of the gallery. As time proceeds and the core swells, the plugs slide in the longitudinal direction and rotate, as occurs in a gravity wall under earth pressure. The vertical stress at the bottom is therefore higher close to the backfill and lower or even null close to the core. Despite the self-weight of the plugs and the effect of


rotation during core swelling, the contact stress remains below 0.30 MPa. This limits the effectiveness of the concrete plugs as confining elements whatever is the value considered for the interface friction angle.


Backfill


(hidden) Plug


Core


Swelling pressure [MPa]


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