Research On Evolution Of Destruction Fractures In Coal Mass With The Conditions Of Temperatures And Pressures

The coal fire in our country is serious,which has seriously destroyed the coal resources and the ecological environment.The development of coal seam crack evolution and coal fire influence each other.Therefore,to study the law and influencing factors on the coal rock fracture development,reveal the coal fire burning mechanism has an important significance for controlling the development of the coal fire area.This paper study the evolution law of coal temperature and pressure of the fractured with Xinjiang Liu Huanggou coal fire area as the research object,analyses of coal fracture development mechanism,characteristics and process of change.The effect of temperatures and pressures on fractures in coal mass is analyzed theoretically.The mathematical model of coupling of coal mass with temperature and pressure was established.Testing the thermodynamic parameters of coal mass and using RFPA numerical simulation software to simulate the thermal damage of coal samples under the coupling of temperature and pressure.The set pressure value is closer to the peak strength of coal sample,and the temperature change is more obvious when the temperature increases.When the pressure is small,the failure rate of the coal sample is maximum at about 140?,when the pressure is large,the failure rate of the coal sample is maximum at about 80 ??Using MTS-880/25t electro-hydraulic servo test system,acoustic emission instrument,industrial CT scanning system tested four coal samples(4 samples per group)which were treated with constant temperature under normal temperature?80??140??200?.The mechanical properties and fracture development of coal are obtained.The higher the temperature,the more discrete the stress-strain curve,the peak strength and the elastic modulus of coal samples increases with temperature and then decreases,It reaches the maximum at 140?.When the specimen is damaged,its strength will be lower.Acoustic emission signal is strongest at peak,the higher the temperature,the less the acoustic emission signal,the number of peak value of acoustic emission increases with the increase of temperature and then decreases,while the energy decreased first and then increased,80 ? is an abrupt temperature point.With the increase of temperature,the fracture was reduced and the failure energy was increased.Each group was subjected to CT scanning with no pressure,50KN,80KN single axis constant pressure.The results show:The crack length and width increase with the increase of temperature under pressure,reached the maximum value at 140?,the maximum length and width is about 20mm,0.6mm.At the same temperature,the development of crack is the most obvious before the peak strength.The increase of pressure will increase the damage rate of coal at the same temperature and accelerate the fracture of coal.The LFA457 was used to measure the physical parameters of coal samples which were treated by mechanical experiments in the temperature range of 30-200 ?.The results show that the thermal diffusivity decreases with the increase of temperature,the thermal conductivity and specific heat capacity increase with the increase of temperature,The sample of 140 ? reach the maximum value.The higher the temperature,the less the change of thermophysical properties.Based on the comprehensive experiments and numerical simulations,it is found that the 140 ? is the temperature of the crack development.