Research On The Mechanism And Technology Of Static Directional Fracture Of Rock

Static blasting technology has the advantages of no noise,no vibration,no fly stone and no dust,is widely used in geotechnical,transportation,mining,water conservancy and hydropower engineering.In view of the fact that the expansion stress is uniformly distributed around the circular hole and it is difficult to control the direction of the crack propagation,then the mechanical mechanism,experiment and technical research of the single hole and porous structure with different shapes are carried out.The analysis shows that the micro crack is in a higher compressive stress,tensile force and friction between the pillars and the hore wall,then with the increase of the expansion force,a plurality of microcracks are expanded into macroscopic cracks.A mathematical model of static expansion force with elliptical hole and rectangular hole is established,Obtained by calculation: The stress concentration factor at the corner of the long axis of the ellipse hole is 3-9 times,and the stress concentration factor at the four sharp corners of the rectangular hole is 7-9times.Based on this conclusion,two basic conditions for the static directional cracking are determined: the crack location is determined and the expansion force is concentrated perpendicular to the crack direction.Based on the characteristics of easy formation of concrete,a series of concrete specimens with circular holes,elliptical holes,rectangular holes and simulated rectangular holes and diamond hole steel mold are respectively poured and tested respectively.The results show that the other shaped charge holes have certain directional effect compared with the circular hole,and the directional effect is that the rectangle hole is weaker than the diamond hole,and the diamond hole is weaker than the elliptical hole.Moreover,the mechanism of rock fragmentation with multiple rows of circular holes is studied,and it can also play a directive role.At the same time,The temporal and spatial distribution of crack propagation is recorded and analyzed by acoustic emission instrument.The density of AE events can well reflect the path of crack propagation:More cracks appear in the middle of the borehole,then extend to the free surface of the hole until it extends to the edge.The stress field distribution and crack growth areanalyzed by ANSYS finite element software,and the simulation results are in good agreement with the theoretical analysis and experimental results.Finally,numerical simulation and physical model experiment are carried out on the repair of roadway section and tunnel holing in practical engineering and so on.