| Due to the influence of complex geological process and mining blasting,some rock masses have the risk of falling off the parent rock,which seriously endangers the safety of workers.In view of the safety detection of the mining face roof,based on the traditional roof safety detection "knock on the roof" operation discrimination mechanism,this paper puts forward a method to judge the safety of the roof in mining face by the audio signal and rebound vibration signal generated by the way of impacting roof rock mass,which based on the way to judge the roof safety by traditional artificial detection mechanism of knocking the roof.This paper mainly adopts the method of combining theoretical analysis,laboratory test and field test to carry out impact test on rocks in different fracture development states.The noise reduction and FFT transformation were carried out respectively for the audio signal and the rebound vibration information generated by the impacted rock.The characteristic parameters of the amplitude and frequency in the spectral maps were analyzed,and the evolution law of their performance with the development of fracture was summarized.The main results and conclusions are as follows:(1)It is found that the sound signal of marble,granite and limestone varies obviously with the development and expansion of cracks in the process of compression through uniaxial compression tests.Based on this,combined with the artificial criterion of the "knock roof" method of mine to judge safety of the roof rock mass,the intelligent detection roof safety information identification features are screened and designed.Based on thin shell theory and cantilever beam theory,the quantitative relationship theoretical model between crack propagation and detection information is analyzed(2)In the laboratory test of rock damage detection,the rock specimens bearing different stress levels of dry,natural and saturated state were impacted respectively,and the amplitude of the feedback audio signal showed a nonlinear increasing trend;Audio frequency increases slightly during loading.Secondly,due to the weakening effect of water on the rock strength,the amplitude and frequency of the audio produced by the saturated specimen after being washed are higher than those of the other two kinds of rocks.(3)The rock specimens with prefabricated cracks at different angles and different crack depths were tested with audio frequency.Within the test range,with the increase of the Angle between the impact direction and the crack,both the audio frequency and the amplitude increase non-linearly.The audio amplitude generated by the rock at 90° crack is the largest,while that generated by 45° is the smallest.The audio frequency is also the largest and the smallest as that generated by 90° and 45° crack.Within the test range,with the increase of slot depth,the amplitude and frequency of the audio frequency show an opposite trend,that is,the amplitude gradually increases and the frequency gradually decreases.(4)The rebound vibration tests of the impact bar were carried out on rock specimens with prefabricated cracks at different angles and depth of cracks.With the increase of the crack Angle and the crack depth,the amplitude of the rebound vibration signal decreases non-linearly.Within the test range,the amplitude reaches respectively the minimum value at 90° and 8mm.According to the relationship between the amplitude of sound signal and the amplitude of rebound vibration signal with the change of the state of the crack,the comprehensive judgment parameter ? of the amplitude of sound signal and the amplitude of rebound vibration signal is established,so as to improve the reliability of the judgment and lay the foundation for the multi-sensor fusion of detection technology.(5)Field test results and laboratory tests are mutually verified.Through inductive analysis of the test data,it is found that with the decrease of the safety of the roof,the audio amplitude increases gradually,while the audio frequency decreases accordingly.The amplitude of rebound vibration signal decreases gradually with the decrease of roof safety.According to the variation of each signal characteristic parameter,the fuzzy judgment interval and the comprehensive judgment interval based on ? value of roof safety are established.This method,which replaces human senses with acoustic equipment and vibration detection device,and numerically processes the audio signal and bounced vibration information,increases the accuracy of detection results.The research results lay a foundation for intelligent detection of roof safety,and provide a theoretical basis for the manufacture of roof detection equipment in intelligent mine construction. |
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