2019_EJRNL_PP_ASA_FRANSSON_1.pdf
Terbatas Resti Andriani
» ITB
Terbatas Resti Andriani
» ITB
The Bentonite Rock Interaction Experiment (BRIE) was performed in a tunnel at a depth of 420 m at the Äspö
Hard Rock Laboratory in Sweden. The experiment focused on the hydraulic properties of rock and bentonite
aiming at investigating the exchange of water across a bentonite-rock interface. The hypothesis for the mechanical modelling presented here was that changes in flow (observed in rock and on bentonite parcels) were
due to local mechanical deformation. Induced stresses related to the construction (and experimental) stages for
the BRIE site such as excavation of tunnels, drilling and over-coring of two vertical, tunnel-floor boreholes and,
finally, installation and swelling of bentonite, were expected to be the main causes of these deformations. We
assumed that this could be investigated using a step-wise rock mechanical modelling approach (with a relevant
modelling sequence) and validated by using a transdisciplinary approach including field structural geological
mapping (geometric, kinematic and dynamic interpretation of the exposed fracture sets) and hydrogeological
investigations.
For key fractures intersecting the boreholes, the modelled fracture normal and shear displacements were
found to be local, small, and in line with field observations and measurements for BRIE. Results point at an
agreement between the spatial locations of changes in flow identified from the bentonite parcels and the locations of inelastic deformation indicated by mechanical modelling for a reverse stress regime. Besides providing
information about the key fractures, the structural mapping allowed to establish solid relationships between
brittle structural features in the tunnel and in the cores, which were used as, or compared to, the main fracture
input to the rock mechanical modelling. The identified fracture sets were found to be structurally reconcilable
with the larger-scale tectonic picture of the area.