Study On Multi-field Coupling Mechanism Of Rockburst-induced Disaster Evolution

The current research on coal-like dynamic disasters mainly relies on the analysis of coal rock deformation and the characteristics of acoustic signal response characteristics during coal-rock failure.It is an important method to study the impact disaster mechanism of coal-rock dynamic disasters.Laboratory-scale coal and rock instability research mainly relies on characteristics such as strain,acoustic emission and electrical resistance to evaluate the dangerous state of coal and rock.Through the analysis of the monitoring signals in the process of coal rock damage to instability,it is possible to provide early warning of the danger level of coal rock before it is destabilized,and reduce the damage degree of coal rock dynamic disasters.However,at present,most of the strain monitoring of coal and rock samples adopts the method of DIC or surface-attached resistance strain gauge to monitor the strain changes in the process of coal and rock damage in real time.The change characteristics of internal strain as the main factors of coal rock instability and disaster are less studied,and there are limitations caused by the inconvenience of monitoring methods.Based on this,this experiment builds an internal strain-acoustic emission joint monitoring experimental platform,uses Bragg grating for packaging,and puts it into the bore of the sample by way of embedding the borehole.The deformation of the internal structure during the load deformation process of the sample Reflecting the strain change characteristics of the sample,the following conclusions are drawn.(1)There is a good correspondence between the acoustic emission signal of the sample and the destruction process of the sample during the damage of the coal sample.The acoustic emission signal of the coal rock sample responds at a low value during the initial loading,and the value of the acoustic emission signal increases significantly as the loading progresses and shows a different response characteristic with the acceleration of the loaded stress of the sample.The acoustic emission signal assignment and signal density of coal rock samples are obviously greater than the acoustic emission signal value during the force maintenance phase.Before the instability of the sample,the acoustic emission count and energy value of the sample showed a large increase trend.The acoustic emission count and energy value of the sample reached the peak at this stage,and the sample was completely deformed and unstable.(2)The internal strain change characteristics of the coal rock sample have a good reflection on the structural yield of the sample.There are a large number of original pores in the sample in the early stage of the load.Under the action of the axial force,the pores are closed with a large amount of stress.The internal strain of the specimen shows a "step" shape with the loading of stress;as the load-bearing force of the sample increases,the "step shape" gradually weakens.At this stage,the internal compactness of the sample increases and the plastic characteristics are weaker than the first stage.The sample's internal strain value showed short-term stability characteristics with the increase of stress before the sample was destabilized,and then showed an increasing trend again.The cumulative strain of the sample increases gradually as the loading progresses,and the increase in the early stage of the sample instability increases significantly;The strain gradient of the sample undergoes a high-speed growth stage,a stable stage,and a rapid growth stage before instability as the loading progresses;The strain rate of the sample gradually decreases as the loading progresses,showing an abnormally increasing trend before destabilizing.(3)The resistance change of the sample and the deformation of the internal structure of the sample have a synchronous response characteristic during the failure process of the coal sample.When the internal crack of the sample yields under the force,the resistance cloud map reflects the The resistance decreases.When the sample begins to crack and the crack starts to expand,the resistance in this area increases significantly.And the resistance cloud before the instability of the sample reflects that the instability of the sample is mainly caused by a large amount of yielding of the internal structure.(4)Through the joint analysis of the crack field and strain field of the sample,it is concluded that the failure of the sample under load is a process of damage accumulation.Small energy events have a cumulative effect on large energy events,that is,the aggregation of small rupture events produces large rupture events.The large energy event of acoustic emission is the result of large cracks and local instability in the sample.The high-resistivity region of resistivity has a good correspondence characteristic with the area where the acoustic emission event of the sample is concentrated.The change in the internal strain of the specimen is also due to the characteristic response of the structural yield due to the damage of the specimen.By combining the internal strain-acoustic emission-resistivity,it can be concluded that the increase in the strain of the specimen is synchronized with the increase in the acoustic emission signal value of the specimen to a certain extent.According to the change trend of the data of the two,a joint acoustic emission-strain determination model for coal rock instability is proposed,and the fluctuation coefficient C of the impact risk warning parameter W can be verified by experiments when the sample reaches 77%-92% of peak stress Early warning of the instability of the sample.