The predicted EDZs and the hydraulic conductivities in the roof and sidewalls
of the elliptical cavern using the four models are given in Figure3. In
each model, two hydraulic conductivity values are provided: one in x-direction
(sub-horizontal), the other in y-direction (sub-vertical). A geometrical
mean value of the two values is also given. The mean value is calculated
using the equation below:
where Kmean is the mean value; Kx is the hydraulic conductivity in x-direction, and Ky is the hydraulic conductivity in y direction.
In the cavern roof, the predicted hydraulic conductivities of all four
models agreed reasonably well with the measurement results, see Figure
4 and Figure 7. The predicted EDZ is about 0.5m-0.7m from the excavation
boundary. In the EDZ, the modelled hydraulic conductivity is mostly in
the range of
m/s, matching well with the measurement results. In the sidewalls, Model
4 (with blast induced cracks within 0.6m into rock) produces the best results
compared to the measurement results.
The modelled EDZ is about 0.7m and the modelled hydraulic conductivity is about m/s, both are in general agreement with the measurements. Other models
with no or smaller blast damage zones have predicted EDZs in the sidewalls
smaller than the measurements, depending purely on the assumed extents
of the blast damage. The stresses (tensile or compression) in these zones
are not high enough to cause fracture initiation.
Overall, the FRACOD modelling results agree well with the permeability
measurement data at Room 425, particularly in the cavern roof and floor.
The numerical results also indicate that blast damage dominates the EDZs
at sidewalls but has little effect on the EDZs in the roof and floor where
damage is caused by stress concentration. At AECL’s URL, a Blast Damage
Assessment Tunnel was excavated and investigated (Martino and Chandler,
2004). It was found that the blast damage can extend up to 0.5m into the
walls. Therefore, the assumption of blast damage zone of 0.4m-0.6m in Models
3 and 4 is considered to be reasonable. |