| Collapse columns directly affect the efficiency and safety benefit of coal mining.Seismic exploration has been proved to be an efficient geophysical exploration method for geological anomalies in coalfield,but the key premise is to clarify the characteristics of seismic wave field in coalfield collapse column and reveal the propagation and transformation mechanism of seismic wave in coalfield collapse column in full space condition.Therefore,based on the elastic wave equation simulation to study the different buried depth,velocity,and presence of cavity status inside the collapse column under seismic wave propagation and waveform transformation law of collapse column,comparison and analysis the different response of collapse column model,and downhole field test and effective detection of collapse column,the specific research results are as follows:For coalfield collapse column diffraction characteristics of seismic wave field,based on the elastic wave equation simulation to study the different buried depth,velocity,and presence of cavity status inside the collapse column under seismic wave propagation and waveform transformation law of collapse column,comparison and analysis the differences of different models of kinematics and dynamics response,conducted field test and use inversion imaging method to effectively detect coalfield collapse column,Specific research results are as follows:(1)In the two-dimensional simulation,combined with the wave field snapshot and signal record,it can be seen that the P-wave generated by source excitation reaches the boundary of the collapse column,forming a diffraction wave at the fault point on the left wall of the collapse column,and the p-wave reaches the vertex of the collapse column,forming a diffraction wave at the vertex.With the continuous propagation of P wave,the diffraction wave of the front bottom Angle depression point is generated at the left bottom corner of the collapse column.With the increase of propagation distance,the diffraction wave of the rear bottom Angle depression point is generated at the right bottom corner of the collapse column.(2)Through amplitude and time-frequency analysis of effective collapse column signals obtained by two-dimensional simulation,it can be concluded that the strong energy region of X component signals is more concentrated than that of Z component signals.The two main regions of strong energy in seismic signal recording are the peak diffraction wave and the fault point diffraction wave.With the increase of the buried depth of the collapse column,the frequency width of the strong energy region of the time spectrum of S transformation also becomes wider.(3)In the THREE-DIMENSIONAL simulation,the root mean square amplitude variation of the three components of diffraction wave was compared,and it was found that the X component of the three components had significant abnormal response to the collapse column.By comparing the time-frequency energy distribution characteristics of the three components,the X component had the most concentrated frequency.The imaging effect of X-ray diffraction migration on collapse column is the best among the three components,and the X component can be used as the effective component for actual detection.At the same time,the difference characteristics of seismic wave field between the collapse column under the coal floor and the collapse column developed into the coal seam are compared.The reflected in-seam wave of the collapse column is the characteristic wave,which can be used for practical downhole detection.(4)combined with 2 d and 3 d numerical simulation results,the scene of the downhole seismic detection tests,the X component signals along coal seam working face toward the inversion results can identify areas of collapse areas,the measured data inversion results explain the collapse column area and the ore party reveal actual drilling data,borehole collapse column detection results to guide the safety in mining face. |
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