Experimental Study On Permeability And Acoustic Emission Characteristics Of Water-cut Coal Seam With Different Loading Rates

It is generally known coal containing gas dynamic disaster is one of the most serious disasters in coal mine in our country,and coal and gas outburst accident comes first.In production practice,original stress balance transfers,in which vertical stress of coal is increased to exceed the load limit and at the same time horizontal stress is reduced as a mining-induced mechanical process.When it happens coal and gas outburst,it is propagated by sound waves from changes of coal and stress as warning information.In this paper WYS-800 microcomputer control electro-hydraulic servo tri-axial gas seepage device is used,combined water,gas and mining stress in different loading rate.In the loading process mechanical properties,evolution law of seepage properties and acoustic emission characteristics are researched.The concrete research content reads as follows:(1)Under different loading rate,stress and strain of specimens are demonstrated nearly similar.Loading rate increased,axial stress peak is decreased obviously.There is volume dilatancy in loading process.(2)Under the conditions of gas pressure 1MPa,confining pressure unloading rate 0.01 MPa/s,increasing loading rate,seepage rate and permea bility of coal present a nonlinear increasing trend while increase rates are decreased.The relation between loading rate and both seepage rate and permeability is better characterized by exponential function k=a-bc~x.The higher water content,the better fit.(3)Increasing loading rate,permeability and seepage rate are increasing.The specimen with low moisture content has a greater increase than one with high water content.Under the condition of the same moisture content,the faster growth rate of loading,the greater amplitude the permeability and percolation rates are increased by.Coal and gas outburst accident is prevented by increasing the moisture content in the coal seam.Permeability under different moisture content shows a downward trend as a result of coal mechanical properties changes by water.Quadratic polynomial relation is better fitted between moisture content and permeability.The greater the loading rate,the better the fitting.(4)In the initial process of the coal gas seepage,there are short intermittent periods between acoustic emission signals while in short intermittent period signals are weak.With the increase of water content,acoustic emission signals are showed a increase in the initial gas seepage process.(5)In the loading process under different moisture content conditions,trends of stress change and AE count rate are almost unanimous.Damage evolution mechanism is well reflected by AE count rate at the same time.As the moisture content increases,the peak stress and accumulated acoustic emission count show a decreasing trend,which shows water content has a dramatic effect on the characteristics of acoustic emission.Contrasting loading process under different loading rates,there is a significant effect loading rates having on acoustic emission.The higher loading rate,the more number of acoustic emission events,the higher average amplitude.Before specimen is damaged,number of acoustic emission events is acutely increased,until the destruction.The power function is available to show relationship between loading rate and accumulated acoustic emission count.The purpose of the paper is using acoustic emission technology to capture valid acoustic as warning information to analyses and monitor.It is of practical significance to monitor coal internal failure mechanism and optimize prevention measures in the coal containing gas dynamic disaster.