Study On Mechanism Of Rock Burst And Early Warning Of Ground Pressure By Mining In The Deep Of Tonglushan Mine

Tonglushan Mine is a kind of hard rock mine,which has the largest mining depth in metal mines of Hubei province.When the mine enter to the deep,a series of geological phenomena caused by high in-situ stress are appeared,and the rockburst disaster is possible to appear.To predict and prevent this disaster,study the mechanism of it is of great significance.Because the rockburst disaster is mainly affected by geostress and the lithology of the surrounding rock,if the paper start study from this two aspects,the mechanism of deep rockburst in Tonglushan Mine can be revealed comprehensively.The main research content of the paper is as follows:(1)The distribution law of in-situ stress in typical area of Tonglushan Mine was studied by the method of “spot-surface combination”.The “surface” method refers to obtain the overall understanding of the distribution law of in-situ stress based on the knowledge of engineering geology and tectonic geology.The “spot” method refers to measuring the geostress by kinds of in-situ stress measurement methods,such as acoustic emission method(AE)and deformation rate analysis method(DRA).The results show that buried depth below 750 m is in the state of high geostress,and the rockburst disaster is possible to occure.In the process of geostress measuring,the current rules of in-situ stress measurement for AE and DRA method are improved,and a new AE-DRA combined in-situ stress measurement scheme is proposed,which can further improve the accuracy and reliability of the the geostress measurement results.(2)To obtain the physical and mechanical properties of typical surrounding rock of Tonglushan Mine,a great deal of experiments have been carried out,such as X ray diffraction,rock sheet identification,block density experiment,rock longitudinal wave velocity measurement,tensile strength test,uniaxial compression deformation test,uniaxial compressive strength test,rock direct shear test and so on.Through carrying out these tests,we can found the typical rocks such as marble and quartz diorite porphyrite in the deep part of Tonglushan Mine are both brittle hard rocks,which can store elastic strain energy well and have the lithologic conditions for the occurrence of rockburst.(3)Based on the research results of the physical and mechanical properties and the in-situ stress value measured in the early stage,the tendency of rock burst in the deep area of Tonglushan Mine was studied.The results show that there is a possibility of more than moderate rockburst in the deep area of Tonglushan mine.When the buried depth is less than 1010 m,the grade of rockburst is moderate,while when the buried depth is more than 1110 m,there may be a strong rockburst.The probability and the intensity of rock burst will increase when the buried depth increase.It should be noted that because of the low uniaxial compressive strength of rock at the depth of 870 m,a strong rockburst may occur.(4)In order to study the mechanism of the rockburst in Tonglushan Mine,uniaxial loading experiment was used to simulate pillar rockburst,and true triaxial unloading experiment was used to simulate strain-type rockburst.During the test,the stress,strain,and the acoustic emission parameters was monitored simultaneously.And high-speed photographic equipment and scanning electron microscope were used to monitor the failure characteristics of rock samples in rockburst tests.The results show that when the rock burst occurs,the specimen is mainly subjected to tensile and shear failure,and the failure process can be summarized as follows: split plate,shear block and block ejection.(5)The Fast Fourier transform(FFT)and short time Fourier transform(STFT)were used to process the waveform file of acoustic emission in ruckburst test,so the frequency characteristics can be analyzed.The results show that the stress concentration caused by excavation and unloading will cause great damage to rock mass,which is an important factor leading to rockburst,and there is no necessary relation between the main frequency of acoustic emission of rock burst and the loading stress.The frequency domain information of acoustic emission can more comprehensively reflect the damage evolution of rock,which can make up for the lack of acoustic emission parameter analysis method.(6)Based on the research results of rock burst mechanism and the engineering situation of Tonglushan Mine,a scheme of rock burst prevention and control is put forward,which is composed of rockburst monitoring and rockburst control.The monitoring of rockburst should be based on regional monitoring,and supplemented by site monitoring.The regional monitoring can use the microseismic monitoring system,and the stress and displacement monitoring system can be arranged to monitor the site at the same time.According to the field monitoring results,the rock mass section with tendency of rockburst occurrence can be determined,and then some control measures should be taken for this part.