On the Initiation Delay Timing in Raise Blasting

摘要

Raises, such as ventilation raise, man-way raise, ore-pass, drop raise in open sloping, etc., are important structures in underground engineering. While some critical raises can be drilled directly by raise boring machines, most raises are developed by regular drilling and blasting method. In general, raise driving is one of the most difficult operations in rock breakage by drilling and , blasting until the long-hole method came into use. With its safety and efficiency of driving the raise in one shot by long-hole blasting, the reasonable blast-hole delays are the key parameters of this method. The minimum initiation delays of blast-holes could be such (hat the rock fragments have been sufficiently evacuated out of the raise before the consecutive blast-holes are initiated. Otherwise the choking and recompressing of the rock in the zone of the cut are possible due to lack of swelling space. Based on this principle, two-phase fluid flow model has been developed to calculate the delay time in this paper. In this model, besides the gravity, the drag forces between the detonation gas products and the fragmented rock play a key role for the evacuation of the rock fragments. In other words, due to the drag force, one-dimensional unsteady state flow of the high-pressure detonation products leads to the acceleration of the movement of rock fragments in the raise. The established model was used to test typical blasting delays in drop raise of 20m to 30m in length. The 300～540ms timing delays obtained by this model are good agreement with the experience in the field. With the designed computer program based on this model, the motion of rock fragments in the raise for any blasting pattern, explosive and rock can also be simulated.