| With the continuous increase depth of coal mining in China,some coal mines have evolved from low gas to high outburst.As one of the effective measures to improve the gas permeability of coal seams,deep hole pre-split blasting has been widely used.However,it is found in the research practice that there are some problems such as poor blasting effect,fast closing of cracks,poor aging of antireflection,etc.which affect the blasting effect when hole pre-cracking blasting of soft and high gas coal seam buried deep in the middle of hard floor.In view of the above problems,this study proposes a method of anti-reflection enhancement by deep-hole controlled blasting of coal seam floor in deep mine.Through the combination of theoretical analysis,laboratory test and numerical simulation,this paper has realized the investigation and experimental study on the influence of blasting hole distance from coal-rock interface,buried depth,control hole location and blasting charge column structure on blasting coal and rock damage and fracture evolution.The main research contents and conclusions include the following:The research reveals the mechanism of deep hole controlled blasting of coal seam floor in deep mine.A model of explosive stress wave propagation of rock dynamic failure criterion are established,and the damage range and fracture extension length of rock after blasting are analyzed.A "hard rocksoft coal" blasting model is established,and the stress wave propagation rule after blasting with different media is investigated.A rock mass blasting model under loading state is established,and the influence of in-suit stress on rock blasting stress wave propagation and crack propagation is investigated.The variation law of blasting stress field after the layout of control holes is studied,and the influence of control holes on the blasting cracking range of coal and rock is analyzed.The formation condition of shaped charge jet is analyzed,the directional rock breaking effect of shaped charge is studied,and the blasting effect of the new supershaped charge with auxiliary charge structure and the traditional shaped charge is compared.The relationship between strength and ratio of similar materials was studied.The effects of sandcement ratio and cement-gypsum ratio on mechanical parameters of similar materials were studied.According to the similarity theory,the proportioning materials and parameters of coal and rock mass in blasting simulation test are determined.The dynamic compressive strength of similar materials was studied by SHPB equipment,and the relationship between dynamic compressive strength and impact pressure was obtained.The dynamic strength and static strength of materials were compared,which provided the test material basis for laboratory simulation research.The results show that the greater the proportion of binder and cement,the greater the compressive strength of similar materials,and the relationship is approximately linear.The greater the impact pressure,the greater the dynamic compressive strength of similar materials,and the dynamic compressive strength is greater than the static compressive strength.The gas-solid coupling bidirectional loading experimental system is used to carry out the blasting similarity simulation test,and the macro-crack,dynamic strain data and ultrasonic wave velocity after blasting are collected for comparative analysis,so as to study the effects of the distance from the blasting hole to the coal-rock interface,the size of in-situ stress,the distance from the control hole to the coal-rock interface and the charge structure on the damage and crack evolution of the cracked coal after blasting.The results show that the closer the blasting hole is to the coal-rock interface,the more concentrated the blasting energy is on the coal body and promotes the upward expansion of the crack.Compared with d = 80 mm,the blasting hole distance d = 20 mm increases the damage to the near area of the coal body by 2.46 times,the damage to the far area of the coal body by 1.77 times,and the damage to the floor is reduced to 0.77 times.The peak value of compressive strain and tensile strain increased by 1.67 and 2.01 times.The ground stress has obvious inhibition effect on blasting crack growth,and the higher the ground stress is,the more obvious the inhibition effect is.With the increase of buried depth,the number of blasting cracks decreases,the width Narrows,and the expansion range decreases.When the buried depth H is increased to 1200 m,the damage to the near area of the coal body is reduced by 78.26% and the damage to the far area is reduced by 68.75% compared with the blasting model without in-situ stress.The peak compressive strain and tensile strain after blasting in the non-ground stress model are 2.27 and 3.27 times of the buried depth H = 1200 m model.The placement of control holes can effectively improve the evolution ability of blasting cracks by guiding the propagation of blasting cracks and providing space compensation.When the control hole is close to the coal-rock interface,the influence on the near end of the coal body is most significant.The peak value of the damage and tensile strain in the model D = 20 mm is 1.93 times and 1.79 times of that in the model without the control hole.When the control hole is far away from the coal-rock interface,the influence on the far end of the coal body is most significant.The peak value of the damage and tensile strain in the model D = 80 mm is 1.53 times and 1.55 times of that in the model without the control hole.When the control hole is placed in the crack zone of deep coal,the influence range of crack is the most significant.The use of shaped charge blasting can cause directional damage to the test block,effectively crack the coal body and reduce the damage to the bottom plate.The damage to the near and far regions of coal body by using supercharge is 2.53 and 3.22 times that of ordinary charge,and the peak compressive strain and tensile strain are 2.08 and 2.44 times that of ordinary charge.The blasting effect of crack coal is as follows: supercharge charge > circular charge charge > linear charge charge > slit charge > common charge.ANSYS/LS-DYNA numerical simulation software was used to compare and analyze the supercharged charge coupling control hole with the ordinary charge blasting.Based on the numerical results of model damage cloud,effective stress cloud,model energy change,stress-time history curve of measuring point,speed-time history curve of measuring point and displacement-time history curve,etc.,The influence mechanism of deep hole controlled blasting on coal cracking,rock damage and fracture evolution of high gas and low permeability coal seam in deep well is further studied.The results show that stress concentration can be formed in the connection area between blasting hole and control hole by using shaped charge and setting control hole.The peak value of effective stress in stress concentration area is 2.23 times that of ordinary charge,and only 0.48 times that of non-stress concentration area.A large number of cracks spread in this area,forming an approximate "inverted triangle" crack damage area,increasing the crack range of coal by 30 cm,effectively improving the anti-reflective effect.The research results provide a theoretical and experimental basis for deep coal seam using floor blasting technology to improve reflection,so as to prevent and control gas disasters such as coal and gas outburst and ensure safe and efficient mine production.Figure 118 Table 43 References 152... |
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