Fig. 1.

(a) Simulation of a PST experiment during self-sustained crack propagation (3 m of a 5 m long column is shown, crack tip at 2.2 m, red dashed line). Colored by its normal displacement (colored from no displacements in orange to 0.5 mm displacement in blue). (b) Simulation of PST during crack initiation phase, the snow saw is represented in dark grey. (c) Internal weak layer fracture process around the fracture process zone. Weak layer and slab were partly removed for visualizing broken bonds in the weak layer (in red; crack tip at 2.2 m)