Thermodynamic Parametric Test And Analysis Of Thermal Instability Characteristic Of Siltstone Of Coal Fire Area

There is a large area of coal field in Xinjiang,Shanxi and other places,which not only burn a lot of coal resources,but also seriously damage the fragile ecological environment in Western China.The evolution process of coal combustion,fire area upper overburden rock fracture,the formation of a new area for air channel is considered to fire one of the main factors to sustainable development.The fire is burning fire fractured coal original force structure changes and the coupling interaction under the change of rock thermodynamic parameters results.Understanding the variation of fire rock temperature peak stress,elastic modulus and other thermodynamic parameters,analyze the heat changing with temperature instability characteristics,which has very important significance to reveal the evolution mechanism of coalfield.Coalfield fire area of overlying strata of sandstone,siltstone,mudstone,sandstone and mudstone at present for the research and study of siltstone rarely.Therefore,the fire powder sandstone as the research object,carry out analysis and study on thermodynamic parameters and thermal instability characteristics of cooling conditions and experimental thermodynamic parameters,whic promotes the understanding of laws of the fire combustion fracture,numerical simulation of fire control and provides some guidance.This paper focuses on the coal fire siltstone,carried out in situ,uniaxial and X diffraction experiment,the main research contents and results are as follows:High temperature and high pressure three rock triaxial test machine of siltstone in low confining pressure(2MPa),within the range of room temperature~600℃ was carried out in situ experiments,found in the room temperature to 600℃,siltstone permeability showed a "V" shape evolution trend with the increase of temperature in the heating process,the permeability in siltstone 300℃ showed a clear threshold value characteristic,the permeability decreases before 300℃,the permeability began to increase after 300℃;combined with the analysis of acoustic emission characteristics and experimental thermal properties,permeability are caused by the phase change thermal cracking by thermal expansion coefficient,thermal conductivity and other parameters,which even cause pore structure changing.The MTS810 experiment system which is used as uniaxial mechanical experiment at high temperature,the highest temperature is 800℃,found out heating treatment of siltstone under the condition of peak stress decreases with the increase of temperature on the whole first decreases and then increases and then decreasesagain,elastic modulus increases first and then decreases with the increase of temperature;100℃ amplitude cooling can increase the damage of siltstone compressive ability,and cooling injury influence was weak in low temperature zone at high temperature(400℃~600℃)with great influence;the analysis showed that the peak stress,elastic modulus are caused by phase change,thermal cracking and mineral classification.;Combined with X diffraction analysis,it is known that the cause of brittle fracture of siltstone is not only related to the thermodynamic parameters such as modulus of elasticity,but also to the content of mineral component of calcite,quartz and dolomite.Combining the mechanical parameters,brittleness coefficient and the failure,found out the heating conditions,compression capability of siltstone decreased linearly at room temperature~200 ℃ section,leads to lower overburden compressive capacity balance stress,crack expand further development;200 ℃ ~700 ℃,siltstone gradually turned to brittle failure,although with the increase of temperature siltstone compressive capacity increased,the increase of temperature the amount of burning coal fire more and more big,overburden stress balance structure changed,once more than the peak stress occurs brittle failure,resulting in a large number of combustion fracture,and reached a maximum at 700℃;when more than 700℃,anti deformation ability and compressive ability declined sharply siltstone gradually lose the compressive strength and softening,resulting in a ductile failure of rock again.