In-situ high-speed 3D-DIC experiment on blast-induced second free surface characteristics at initial stage of cut blasting in a tunnel

•An in-situ blasting experiment use 3D-DIC method.•Wide test range, high accuracy, cross scale, massive data for the blasting process.•Evolution law of in-plane and off-plane displacements of rocks in the cut blasting.•The critical displacement criterion for rock failure induced by in-situ blasting.•Dynamic process and properties of forming the second free surface.