In the east pit last week, clean granite with a decoupled charge and solid stemming had me wondering: does initial breakage come more from reflected tensile waves at the free face or shear along preexisting joints? My high‑speed footage shows the crushed zone hugging the hole while thin spall sheets lift off — anyone got field data that says otherwise?
In clean granite with decoupled loads I usually see tensile spall go first; in banded gneiss where joints daylight, shear can initiate early. Try a paired test with +0.3 m stemming and about 10% lower PF — if your “spall sheets” thicken and lift sooner it’s tensile-led, otherwise you’ll see break migrate to the joint planes; were your delays lining up a set?
“thin spall sheets” is what I see when tension leads; I get a clearer read by adding a 0.25 m air-deck under the stemming and switching to 6–10 mm fines — if shear wants to go first it’ll jump to any daylighted joints immediately. What were your collar delays on that row?