Study On The Transformation And Propagation Of Seismic Stress Wave In Coal And Rock Strata

Deep coal mining is seriously affected by coal rock dynamic hazards.Underground blasting,roof fracture or fault activation generate dynamic stress waves in the coal rock body,which can cause coal rock dynamic disasters when coupled with the mining space or tunnel envelope rock.However,there is a lack of in-depth research on stress wave propagation and coupling disaster-causing process,especially whether the roof stress wave can propagate laterally and cause coal wall sheeting or dynamic disaster.In this thesis,we summarize and refine the practical problems,and adopt a research method combining experimental and theoretical analysis to study the axial propagation,lateral transformation and propagation law of stress waves in coal rock layer,and combine the research results to explain the process and mechanism of coal mine site roof breakage triggering punching and dynamic disasters.The main research work and results are as follows:(1)The Hopkinson compression bar experimental system was improved to reveal the axial propagation law of stress waves under axial loading conditions through experimental and theoretical analysis.It was observed that the stress waves(deformation waves)at each measurement point on the specimen were compression waves,and the magnitude was much larger than that of the stress wave signals monitored on the incoming transmission rod,which was mainly due to the fact that the wave impedance of the specimen was much smaller than that of the rod,and it was easier to produce deformation under the action of stress waves of the same intensity,while the stress waves on the transmission rod became small,and the phenomenon was mainly related to the dissipation of stress wave energy in the specimen.According to the characteristics of the stress waves monitored at each measurement point on the specimen,the stress waveform was divided into three parts: rising edge,falling edge and fluctuation section,and then the spatial and temporal evolution of the peak time,amplitude and spectral curve were analyzed.The analysis results show that: the peak time of stress wave is positively correlated with the propagation distance;the amplitude of stress wave increases first and then decreases with the increase of time and space;the incident waves generated at different punch speeds only have differences in amplitude,and the shape of stress wave signals generated at different punch speeds at the same measurement point is more or less the same;the amplitude of stress wave increases gradually with the increase of punch speed;after the fast Fourier transform,the main frequency of stress wave is at 0.After the fast Fourier transform,the main frequencies of stress waves are all located in the interval of 0～1000Hz,and the main frequencies gradually decay with the increase of propagation distance.(2)Through experimental and theoretical analysis,the transverse propagation law of axial stress waves in the rock mass was revealed.It was observed that the stress waves could produce transverse propagation in the rock mass,and each measurement point on the specimen produced compressional stress waves first and then tensile stress waves,and the amplitude of tensile stress waves was larger than that of compressional stress waves,indicating that the stress waves were reflected at the critical surface.According to the characteristics of the stress waves monitored at each measurement point on the specimen,the transverse stress waveform was divided into compressional,tensile and fluctuation sections,and then the peak time,the spatial and temporal evolution of the amplitude and the spectral curve of the stress waves were analyzed.The results show that the peak time of compressional stress wave is positively correlated with the propagation distance;the amplitude of compressional stress wave increases with time and then decreases;the spatial trends of the amplitude of compressional and tensile stress waves with propagation distance are similar to those of axial propagation,but the difference is that the maximum amplitude of compressional stress wave in axial propagation and tensile stress wave in transverse propagation appears at a fixed location.The location of the maximum amplitude of the compressional stress wave in transverse propagation increases with the speed of the punch and gradually moves closer to the critical plane;the peak point of the tensile stress wave is defined with the help of the fitted curve,and it is found that the distance to the critical plane of the peak point of the tensile stress wave is not related to the punch speed;the amplitude of the stress wave increases gradually with the increase of the punch speed,and the amplitude of the stress wave increases slowly with the speed of the punch in the initial stage,but after the speed of the punch is greater than a certain value After the fast Fourier transform,the main frequency interval of the compressed and stretched segments increased significantly compared with the axial propagation,and the compressed segment was located in the interval from 0 to 20,000 Hz,and the stretched segment was located in the interval from 0 to 10,000 Hz,and the number of peaks in the main frequency interval was greatly reduced,and the compressed segment even had only a single peak or double peaks.(3)Using the results of the above research,combined with the engineering case of impact ground pressure at the 92201 working face of Sanhejian coal mine,the mechanism of action of on-site coal wall flake gang,power disaster damage to coal body and pressure relief prevention and control measures are explained.the main reasons for the occurrence of impact power disaster at the 92201 working face include large mining depth,propensity to impact,hard roof plate,presence of geological factors such as igneous rocks and village coal column and mining stress concentration.High roof fracture generates stress waves and propagates in the coal rock layer with high stress concentration,strengthens and turns to propagate in the coal seam of the roadway gang,couples with the high stress gradient area of the surrounding rock,and reflects in the surface area of the surrounding rock to form tensile stress waves,leading to the damage of the coal body flake gang and large scale movement of the surrounding rock,forming impact ground pressure.Coal mines adopt the method of pressure relief by large-diameter boreholes to prevent the occurrence of dynamic disasters by releasing the elastic potential energy in the surrounding rock,reducing its stress gradient,and creating a fracture zone around the borehole to weaken the stress wave and its propagation ability.The research work and results are of great significance for gaining a deeper understanding of the evolution process of the coupling of stress waves and mining space or tunnel envelope rocks in underground coal mines to cause disasters,effectively prevent underground dynamic disasters and ensure safe production.The thesis has 54 pictures,23 tables and 81 references.