Euradwaste '08 - EU Bookshop - Europa

tive crack network, oriented along principal strains, is associated to each Gauss point of the finite
element model. The crack opening is then linked to the tensile principal strains [5].
Because of an anisotropic strain tensor along a borehole, it results an anisotropic permeability tensor.
Applying to the modelling of the long term dilatometer test, this approach permits to well reproduce
the behaviours of indurated clays. An EDZ of few centimetres behind the borehole can be
identified. In this area, a high fracture density, characterized by permeability increases of up to several
orders of magnitude is observed as shown on Figure 6, which represents the axial permeability
along (a) and on a section perpendicular (b) to the borehole after the borehole drilling and for the
different dilatometer loads. Moreover, when dilatometer pressure increases, the permeability decreases
and no significant water flow modification can be observed in EDZ along the dilatometer as
illustrated on Figure 7, which represents the evolution with time of the overpressure in I2 after hydraulic
tests and for different dilatometer loads. Finally, the comparisons between numerical predictions
and measurements of the pressures in the intervals exhibit a good agreement and confirm that
our model is able to catch the main hydro-mechanical processes occurring within the EDZ in
Opalinus clay.
1.0E-14
1.0E-15
1.0E-16
1.0E-17
Kyy (m²)
Packer
Interval I2
(a) (b)
borehole
Dilatometer
dilatometer
loading
increases from
3 to 5MPa
Interval I1
borehole drilling
y (m)
1.0E-18
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5
444
Kyy (m²)
1.0E-14
1.0E-15
1.0E-16
1.0E-17
1.0E-18
1.0E-19
Dilatometer
dilatometer
loading increases
from 3 to 5MPa
x (m)
1.0E-20
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Figure 6: Axial permeability along the borehole (a) and on a section perpendicular to the borehole
in mid-length of the dilatometer probe (b) after the borehole drilling and for different dilatometer
loads
0.16
0.14
0.12
0.10
0.08
0.06
0.04
ΔPw (MPa)
I2 time of reaction
increases with
dilatometer loading
phase 4
Pdilato = 3MPa
phase 8
Pdilato = 4MPa
phase 10
Pdilato = 4.5MPa
0.02
0.00
phases 12 -13
Pdilato = 5MPa
log Δt (s)
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07
Figure 7: Evolution of overpressure in I2 in time after hydraulic tests and for different dilatometer
loads
4. Conclusions
The excavation damage zone is a phenomenon that occurs in the most rock masses as a consequence
of underground excavation. The EDZ appears as an area around the underground openings,
where geotechnical and hydro-geological properties are altered. The numerical model should be