Study On Damage Seepage Law And Disaster Mechanism Of Gas Adsorbed Coal Under Dynamic And Static Load

Seeking resources,energy and space from the deep is an inevitable choice to ensure China’s economic and social development.When deep mining,dynamic disasters such as pressure bump and rockburst occur frequently,suddenly and violently,which is very destructive.Its prevention and control have become a worldwide problem.The scientific essence of this kind of coal and rock dynamic disaster is the damage and fracture of coal adsorbing high-pressure gas and the dynamic effect of gas migration under the superposition of high ground stress and mining disturbance load.However,the existing research is mostly considered from a single perspective of driven load and gas damage to coal and rock mass,and limited to research means the study of coal and rock under dynamic and static superimposed loads is mainly based on SHPB high strain rate impact test.Therefore,this paper has developed a unique test instrument that can realize dynamic and static combined loading and multi field coupling environment simulation from the unique point of view of coal rock coupling damage and instability induced by dynamic load,static load and gas adsorption.The internal relationship between the macroscopic fracture mechanical response of the three to the coal body and the seepage evolution is discussed,and the damage seepage mechanism of the coal body under the superposition of "dynamic load+static load+gas pressure " is revealed.The gas-solid coupling dynamic model of damage seepage considering dynamic load induction and gas adsorption deterioration is established,which breaks through the difficult problems of numerical simulation and physical simulation of coal and gas outburst under dynamic and static superimposed load,and reveals the disaster causing mechanism of dynamic disasters such as coal and gas outburst.1)Based on the shortcomings of the existing instrument system and comprehensively considering the complex disaster pregnant environment and dynamic and static combined stress conditions of coal and rock mass dynamic disasters in deep engineering,a novel mechanics and permeability test instrument for gas bearing coal which can realize dynamic and static coupling loading is developed.The system mainly includes dynamic and static loading unit,triaxial confining pressure unit,fluid injection unit and information acquisition unit.The advanced and innovative features of the test system include:（1）the coupling of low and medium strain rates with multiple static and dynamic loads is achieved.（2）The high sealing performance of the seepage chamber in the process of inflation loading is realized;（3）The synchronous and accurate measurement of circumferential displacement and axial displacement is realized;（4）The rapid replacement of the test piece is realized.2)The damage deterioration test of mechanical properties of gas bearing coal under dynamic and static coupling loading is carried out,and the effects of cyclic dynamic load frequency/amplitude,static load stress stage and adsorbed gas pressure on coal macroscopic damage characteristic parameters such as compressive strength and elastic modulus are studied:（1）With the increase of cyclic dynamic load frequency/amplitude,static load stage and gas pressure,the damage of coal strength and elastic modulus is greater;（2）In the application stage of cyclic dynamic load,coal will produce a certain degree of irreversible deformation,and the greater the irreversible deformation is with the increase of dynamic load,static load and gas adsorption pressure;（3）The acoustic emission and stress-strain curve of coal sample show obvious coupling effect during triaxial compression.With the increase of dynamic load,static load and gas adsorption,the peak values of ring count rate and energy count rate appear in the peak intensity and gradually decrease,and the cumulative ring count and cumulative energy count gradually increase;（4）The strength deterioration of coal and rock mass under dynamic and static load is mainly the process of interaction between dynamic and static load and cracks in coal.The role of static load in the destruction of coal is mainly to change the number of primary,the degree of closure and the energy storage at the crack tip.The main function of dynamic load is to make the fracture brittle expand,so as to cause greater damage,and finally reduce the strength of coal and rock mass.3)The temporal and spatial evolution law of coal permeability under the coupling of multiple factors is obtained:（1）With the increase of dynamic load frequency and amplitude,static load stage（compaction elasticity yield）and gas adsorption,the coal permeability increases gradually;（2）The relationship curves between total stress-strain and permeability of coal and rock mass under different cyclic dynamic load amplitudes are obtained.There is a good coupling relationship between coal sample stress,axial strain and permeability,and the permeability and stress-strain show the phenomenon of same frequency resonance;（3）Coal permeability is highly sensitive to cyclic dynamic load,and the greater the static load stress stage.The dynamic load sensitivity coefficient of permeability decreases with the increase of adsorption capacity of adsorbable gas and increases with the increase of static load stress stage;（4）Considering the dynamic load impact damage,static load damage and gas adsorption damage of coal and rock mass,a coal rock permeability model coupled with dynamic and static load and gas adsorption is established.4)Based on the traditional gas-solid coupling model,considering the coupling effect of dynamic and static load and gas adsorption,the damage evolution equation and permeability evolution equation suitable for gas coal adsorption in dynamic and static multi field environment are redefined.The stress field and seepage field equations of coal and rock mass under the combined action of axial static load,cyclic dynamic load impact and gas adsorption are coupled,and the gas-solid coupling dynamic model of gas adsorbed coal damage seepage is deduced and established.The physical simulation test of coal and gas outburst induced by roadway vibration excavation is carried out on the scale of vertical engineering,and the results are very similar to the field.Taking this as an example,combined with COMSOL software,the gas-solid coupling dynamic model of damage seepage established in this paper is introduced to carry out numerical simulation test.The feasibility of the model and the scientificity of the theory are verified.The research results will help to reveal the damage deterioration and seepage mechanism of gas adsorbed coal under dynamic and static superimposed loads,deepen the understanding of the disasters occurrence mechanism,and play an important role in effectively controlling the dynamic disasters of deep engineering,and ensuring the safety of national energy resources and economic and social development.