Study On Macro Mechanical Properties And Micro Pore Structure Of Coal And Sandstone Under The Influence Of Temperature And Humidity Environment

The temperature,stress distribution,humidity and other environments of deep rocks are obviously different from the ground surface,which causes great difficulties in the complete storage of rock cores.It is found that some cores are easy to be broken in the process of core storage,and the integrity of core storage is very important for the realization of in-situ core storage and ensuring that the formation can show the geological information contained in it with in-situ,complete and clear solid core.Therefore,through theoretical research and experimental analysis,to explore the changes and mechanism of macro mechanical properties of coal and sandstone under the influence of temperature and humidity has important guiding significance for the follow-up study of fragile core fragmentation mechanism and protection methods.In this paper,the macro mechanical properties,mineral composition and pore structure of coal and sandstone under the influence of temperature and humidity are studied by theory and experiment.Firstly,based on the basic mechanical experiments of coal and sandstone,the change laws of uniaxial compressive strength,uniaxial tensile strength,elastic modulus and Poisson's ratio of coal and sandstone under the influence of temperature and humidity are explored;Then,based on the X-ray diffraction experiment and high-pressure mercury injection experiment,the mineral composition and pore structure characteristics of coal and sandstone were obtained and studied.Finally,based on the above experimental data,the equivalent bulk modulus and equivalent shear modulus of coal and sandstone with different porosity are calculated by inclusion theory and homogenization method.Through the measured elastic modulus and Poisson's ratio,the experimental values of bulk modulus and shear modulus of coal and sandstone are obtained,and the theoretical values are compared with the experimental values.The main conclusions are as follows:(1)The splitting strength and compressive strength of coal decrease with the increase of temperature and increase with the increase of humidity;With the increase of temperature,the splitting strength and compressive strength of sandstone first decrease,then increase,and then decrease.(2)The curve of thermal expansion coefficient of coal and rock with temperature can be divided into two stages: rapid decrease stage and slow increase stage;The temperature curve of thermal expansion coefficient of sandstone can be roughly divided into three stages: slowly increasing stage,accelerating increasing stage and slowly decreasing stage.(3)The main mineral composition of coal is quartz,kaolinite and calcite,and a small amount of pyrite,dolomite and gypsum.The main mineral composition of sandstone is quartz,microcline,albite,kaolinite,mica and a small amount of dolomite.(4)High temperature treatment makes coal and sandstone dehydrate and degass,resulting in the effect of porosity expansion,which leads to the expansion and extension of primary cracks in the rock,and makes the porosity of coal and sandstone increase with the increase of temperature.The increase of humidity makes the minerals in coal and sandstone expand,the fractures become smaller,and some micro fractures close,which makes the porosity of coal and sandstone decrease slightly.(5)The theoretical and experimental values of bulk modulus and shear modulus of coal and sandstone decrease with the increase of porosity.Because the theoretical value is calculated by the porosity less than the actual value measured by mercury injection experiment,the theoretical value is greater than the experimental value in both bulk modulus and shear modulus.