Study On The Characteristics Of Strain Rockburst In Sandstone And Its Prevention And Control By Active Pre-splitting

Rockburst as a complex dynamic disaster phenomenon of rock,rock burst is mainly reflected in the instantaneous release of the elastic strain energy stored inside the rock mass,which leads to the rock mass bursting,loosening,spalling and even ejection,bringing a direct threat to the safety of construction workers.Along with the increasing of mining depth,the influencing factors of rockburst are gradually changed.The rockburst destruction is large,the mechanism is complicated,and the prevention and treatment is difficult.So far,many research scholars have achieved certain results on the prediction warning technology of rockburst and the study of rockburst,but the mechanism of rockblast does not perform comprehensive and complete revelation.The control of rock explosion has also rely on engineering practice which does not provide effective prevention measures in a short time.Therefore,through theoretical analysis,numerical simulation and laboratory tests and other research methods,this paper adopts bidirectional shaped charge tensile blasting technology to study the prevention and control of prefabricated crack rock burst in sandstone,and explores a new way of prevention and control of prefabricated crack rock burst.（1）Through the theoretical analysis of the cracking mechanism of different shaped charge blasting modes,the law of stress wave propagation and crack propagation in surrounding rock under four different blasting modes of single hole ordinary blasting,single hole shaped charge blasting,continuous hole shaped charge blasting and interval shaped charge blasting was deeply analyzed,and the superposition equation of peak pressure and stress in surrounding rock was established.（2）Different blasting modes were studied by numerical simulation,and the results show that interval blasting can not only form smooth through cracks along the direction of cumulative energy,but also reduce the construction intensity and the consumption of single hole explosive,save the blasting cost,and have little impact on the surrounding rock.Therefore,the bidirectional shaped charge blasting tensile technique is used to preform the fracture of rock mass containing strain energy.（3）Based on elastoplastic mechanics and through theoretical analysis,the variation law of strain rockburst stress in precracked sandstone is deeply analyzed.Under the influence of initial in-situ stress after excavation unloading,the maximum vertical stress of rock mass is approximately3σ₁-σ₃,and the stress difference is the largest at the excavation boundary surface.The vertical stress of the rock at the frontage can be reduced by cutting the frontage,and the strain energy consumed by the rock mass can be increased by squeezing and closing the rock in the range of cutting,thus reducing the rockburst tendency.（4）The numerical simulation of different slot depth,slot position and slot spacing was carried out.The results show that the best slot depth is 10mm,the best slot position is 55mm from the top of the sample,and the best slot spacing is38mm.The horizontal displacement of the intact sample is about 30%lower than that of the single cut fracture sample,the integrity of the rock mass at the back edge of the single cut fracture sample is 50%higher than that of the complete rock sample,and that of the double cut fracture sample is 10%higher than that of the single cut fracture sample,indicating that the horizontal ejection displacement of rock burst can be greatly reduced by the cut fracture.（5）The laboratory test was conducted on the complete sample,single slit sample and double slit sample.The test results showed that the broken degree of the complete sample was higher after the failure,resulting in 4-5 laminar plate cracks.The integrity of single-slit and double-slit specimens increases greatly,and the plate crack damage decreases to 2-3 layers.The acoustic emission monitoring energy count of the intact sample is 2 times that of the sample with slit.When the confining pressure increases to40MPa,the impact event count of the slit sample increases faster than that of the intact sample,but the peak count is 20%lower than that of the intact sample.The cutting ensures the stability of the rock mass at the back edge and does not affect the stability of the roadway wall.