| Rock mass landslides are famous for their large scale,complex mechanism,harmfulness and catastrophicity,and have attracted the attention of many scholars.It has become a common understanding that the monitoring and forecasting of geological disasters can achieve the purpose of preventing and mitigating disasters.The rock mass contains different types and sizes of fractured structural planes.The failure of rock mass failure is the result of crack propagation of fractured rock mass,and the water content is also affected.The main factor of rock mass rupture.Based on this,this paper studies the distribution characteristics of electromagnetic radiation and acoustic emission signals in different angle prefabricated cracked sandstones and shale under different uniaxial compression failures in the stages of crack compaction,stable expansion,instability failure and macroscopic fracture.The relationship between electromagnetic radiation and acoustic emission changes and deformation and failure characteristics of rock specimens is analyzed.The surface potential characteristics and cloud pattern distribution of pre-cast cracked sandstones and different water-bearing mudstones with different dip angles were studied.The influence of crack dip angle on sandstone and water immersion time on mudstone surface potential was analyzed;and R/S analysis was used.The principle is to process its surface potential signal.The paper has obtained the following main results:(1)The acoustic emission and electromagnetic radiation signals of precast cracked sandstone and different immersion time are closely related to the crack propagation process,and have obvious stage distribution characteristics.The maximum breaking load of prefabricated cracks at different angles is different.In the crack compaction stage,acoustic emission and electromagnetic radiation are mainly caused by the closure of the original crack and micro crack,and the signal fluctuation increases.During the crack expansion and expansion stage,the acoustic emission and electromagnetic radiation signals change little;after entering the crack instability and destruction stage,The microcracks continue to expand to form macroscopic cracks,the signal is active,and the signal fluctuates greatly near the peak of the load;then the load decreases,and the acoustic emission and electromagnetic radiation signals also decrease.Therefore,the acoustic emission and electromagnetic radiation signal changes in the process of rock instability and rupture are of great significance for predicting rock mass landslide.(2)There are differences in the acoustic emission and electromagnetic radiation signal changes during the pre-fabrication crack deformation process of different dip angles,which are mainly related to the deformation and failure characteristics of rocksamples.The sample was cracked at the crack initiation points at both ends of the pre-crack.When the crack inclination angle is 30°,the specimen undergoes shear failure;at this time,the extrusion,friction and slip of the microcrack wall surface are the main causes of acoustic emission and electromagnetic radiation.When the pre-crack angle is60°,the sample is mainly tensile damage,and the signal is mainly generated by the energy release caused by the tensile failure.When the pre-crack angle is 45°,the sample is subjected to shear failure and tensile failure during the fracturing process.Therefore,the electromagnetic radiation and emission signal of the 45° pre-cracked sandstone sample are generated during the crack instability stage.Early,the growth is relatively fast.(3)The acoustic emission and electromagnetic radiation signals of mudstone deformation and failure process in different immersion time were analyzed.The results show that with the immersion time lengthening,the acoustic emission signal is intense and the duration is longer.At the same time,the uniaxial compressive strength of the mudstone is reduced and it is more prone to cracking.However,as the immersion time becomes longer,the electromagnetic radiation signal fluctuates less and the fluctuation time becomes shorter.It may be that water weakens the mechanical properties of the mudstone and makes the mudstone sample structure more compact,resulting in less electromagnetic radiation signal generation.(4)The surface potential signal and the load show good synchronization,which can better reflect the stress state and deformation and cracking process inside the sample.The pre-cracking has a significant influence on the distribution and migration of the surface potential cloud map.The magnitude of the potential change is related to the distance from the potential channel to the crack.The closer the distance is to the crack,the larger the potential change.Therefore,the degree of crack development can be predicted by observing the potential change.(5)Water has a great influence on the physical and mechanical properties of mudstone.It reduces the strength and elastic modulus of mudstone and increases the plasticity,which ultimately reduces the potential amplitude of the loaded mudstone.The longer the soaking time in water,the smaller the potential change.Therefore,by observing the variation range of potentials of different channels,predict the change of water content of mudstone.(6)Based on the principle of R/S analysis,the potential signals generated by pre-cracked sandstone samples at different angles and muddy rock samples with different water content samples were processed,and their Hurst exponents were all greater than 0.5,indicating that the potential signals generally showed an increasing trend.As the soaking time increases,the Hurst index of the potential signal generated by the mudstone rupture process is decreasing.When the rock mass is completely destroyed,its Hurst index is reduced to some extent.Therefore,the Hurst exponent of the potential signal can be rapidly increased to a maximum value as a precursor to the impending instability of the rock,thereby monitoring and warning the rock mass landslide. |
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