Study On Attenuation Law Of Stress Wave Propagation In Gradient Surrounding Rock Structure

Coal burst is a dynamic disaster caused by the sudden release of elastic energy under the condition of high stress concentration,resulting in the destruction and instability of coal and rock mass.Impacting dangerous roadways often adopt support and pressure relief measures such as anchor net cable support,drilling pressure relief,coal seam water injection,blasting pressure relief,etc.to prevent coal burst.Impacting dangerous roadways often adopt support and pressure relief measures such as anchor net cable support,drilling pressure relief,coal seam water injection,blasting pressure relief,etc.to prevent rockburst.As a result,the support zone mainly composed of anchoring medium,the pressure relief zone mainly composed of fracture development medium and the proto-rock zone mainly composed of elastic medium are formed around the roadway.The anchorage zone,pressure-relieving zone and proto-rock zone form a gradient surrounding rock structure.The physical and mechanical properties of the coal-rock medium such as density,strength,and stiffness in the gradient surrounding rock structure of the roadway change in a gradient along the radial direction of the roadway,which controls the propagation and attenuation of the stress wave.In this paper,the stress wave transmission model of the gradient surrounding rock structure is established around the attenuation control of the stress wave by the gradient surrounding rock structure of the roadway by means of theoretical analysis,laboratory tests and numerical simulation methods.The influence law of the incident angle and the medium density of the pressure relief zone on the stress wave energy is theoretically analyzed;The change law of the stress wave was simulated and analyzed with various schemes,Comprehensive utilization of stress wave amplitude attenuation coefficient,wave impedance matching coefficient,energy absorption ratio,energy attenuation coefficient and other parameters,It reveals the control effect of the gradient surrounding rock structure on the propagation and attenuation law of stress wave;Based on the seismic response research method,a vulnerability evaluation method suitable for gradient surrounding rock structures is proposed.Based on the one-dimensional elastic wave theory,the stress wave transmission model of the gradient surrounding rock structure is constructed,and the influence of the pressure relief zone density and the incident angle of the stress wave on the energy coefficient of the stress wave is analyzed.It shows that with the increase of pressure relief zone density,the refracted P-wave energy increases,the reflected P-wave energy decreases linearly,the refracted S-wave energy remains unchanged,and the reflected S-wave energy increases linearly,The pressure relief belt can produce the effect of energy absorption and shock reduction;With the increase of the incident angle of P wave,the energy coefficients of refracted P wave and reflected P wave both decreased first and then increased.But the energy coefficient of the reflected P wave reaches 100% when the incident angle is 90°.As the incident angle increases,the energy coefficients of the reflected S-wave and the refracted S-wave have the same trend,both increase first and then decrease.But refracted S waves eventually decrease to 0%.It shows that the interface between the decompression zone and the compaction zone plays a barrier role in the propagation of the stress wave.The physical and mechanical parameters such as uniaxial compressive strength,elastic modulus,bulk modulus,and shear modulus of the drilled sample were obtained through the test experiment of the mechanical parameters of the coal and rock mass in the drilled hole.The medium parameter basis is provided for the numerical simulation research.The numerical simulation results of the gradient surrounding rock structure show that the width of the pressure relief zone of the gradient structure increases,the amplitude attenuation coefficient increases,the energy attenuation coefficient shows an upward trend,and the stress wave attenuation speed is faster;At the same time,as the row spacing between pressure relief boreholes decreases,the elastic modulus and density of the medium in the pressure relief zone decrease,the proportion of energy absorption increases,and the energy absorption capacity of the gradient structure to stress waves increases;The greater the wave impedance matching coefficient of the "three zones" in the gradient surrounding rock structure,the greater the energy attenuation coefficient,indicating that the greater the difference in the medium properties of the "three zones",the better the energy absorption effect of the gradient structure on stress waves;Under the same condition of gradient surrounding rock structure parameters,the greater the roadway buried depth,the farther the stress wave propagation range,and the slower attenuation;The higher the stress wave energy,the faster the attenuation speed,the more energy absorbed by the gradient surrounding rock structure,and the better the anti-scour effect;The higher the frequency of the stress wave,the faster the attenuation speed,the absorption and vibration reduction effect of the high-frequency stress wave is better than that of the low-frequency wave,and the gradient structure has the characteristics of "high-frequency resistance,low-frequency pass";The decrease of the incident angle of the stress wave leads to a downward trend of the peak acceleration,that is,the smaller the incident angle,the faster the decay rate of the stress wave.Under the same condition of gradient surrounding rock structure parameters,the greater the roadway buried depth,the farther the stress wave propagation range,and the slower attenuation;The higher the stress wave energy,the faster the attenuation speed,the more energy absorbed by the gradient surrounding rock structure,and the better the effect of preventing coal burst.The higher the frequency of the stress wave,the faster the decay,The absorbing effect of high-frequency stress waves is better than that of low-frequency waves,that is,the gradient surrounding rock structure has the characteristics of "high-frequency resistance,low-frequency pass";The reduction of the incident angle of the stress wave makes the acceleration peak value decrease,that is,the smaller the incident angle,the faster the stress wave decays.According to the IDA method,Comprehensive evaluation of the vulnerability of the gradient surrounding rock structure model using the earthquake intensity index PGA and the structural vulnerability index DM.The results show that with the increase of the amplitude modulation coefficient A,the PGA in the gradient surrounding rock structure of the roadway generally shows an upward trend.With the increase of the pressure relief belt width,the PGA index generally shows a downward trend;At the same time,the increase of the row spacing between the boreholes and the decrease of the medium density of the pressure relief zone can effectively reduce the ground motion intensity index PGA,that is,it can effectively absorb energy and prevent erosion of the roadway.The thesis has 68 pictures,42 tables,and 104 references.