Coupling model of stress-damage and its application to static blasting technology

Abstract

To improve the gas drainage effect of low-permeability coal seams, the influence of the hole arrangement on the static blasting effect was studied through single-hole, double-hole, and guiding-hole blasting tests. A stress-damage coupling model was established to reveal the evolution of the stress field and the distribution of the damage zone under different construction parameters, and the evolution law of the damage zone under a multi-hole arrangement was investigated. The following can be inferred from the research results. (1) The crack initiation of double holes depends on the stress superposition between blasting holes, whereas that of guiding holes depends on the free surface inside the coal body. The increase in borehole diameter and spacing reduction between boreholes could improve the static superposition breaking effect. (2) The relationship between the guiding hole, borehole diameter, and borehole spacing was revealed from the two aspects of the stress field and damage zone. The purpose is to strengthen the blasting effect. The drilling diameter and spacing are measured, and the guiding hole strengthens the blasting effect. At the measurement level, it should be analyzed from the two dimensions of time and stress. The time dimension accelerates the migration of the stress turning point, whereas the stress dimension realizes stress superposition and finally strengthens the static cracking effect. (3) The damage zone evolution of static blasting technology is influenced by expansion pressure, construction parameters, and elastic modulus. The increase in the expansion pressure caused the damage zone of the coal body and a decrease in the elastic modulus. Under the combined action of the expansion pressure and elastic modulus, the damage zone expanded and penetrated. The guiding borehole would not only have a guiding function but could also enhance the breaking effect. (4) In the simulation test scheme, the reasonable ratio of borehole spacing to borehole diameter is approximately 13 to 14, and the reasonable construction parameters are 113 mm of borehole diameter, 1.4 m of borehole spacing, and the layout of multi-hole-guiding hole. Static blasting technology can increase the distribution of the damaged areas of coal seams, realize pressure relief and permeability enhancement of coal seams, and improve the safe construction of coal mining.