Fig. 10

Detailed mapping of the tunnel floor and sidewall in Gallery 08 between gallery metre GM 65 and GM 76. For location refer to Fig. 4. The mapping revealed metric-scale, sub-horizontal extensional fractures on the tunnel floor. These fracture surfaces are characterised by a plumose structure with ripple structures and well developed fringe zones (e.g. en échelon or hackle structures) indicating the fracture nucleation point and the propagation direction. Mainly observed on tunnel face, ceiling and sidewall, certain striated fracture planes are not of tectonic origin. Parts of them are associated with other excavation-induced fractures. They dip with angles ranging from 40° to 80° and are systematically more inclined than the bedding planes. These excavation-induced shear planes are associated with down-dip striation indicating normal displacement along the fracture plane