Evolution law of mechanical properties of coal sample structure damage caused by cyclic cold leaching

Pore and fracture structure is an important factor affecting the mechanical properties of coal，which is directly related to the safe production of coalbed methane and other energy. In order to study the change law of me⁃ chanical properties of coal caused by structural damage under the action of liquid nitrogen， the long flame coal from coal mine of Xinqiu in Fuxin city of Liaoning Province was selected as the experimental sample. Through the ex⁃ perimental method of cyclic cold leaching，the rock compression experimental machine and the acoustic feedback structural damage detection experimental device were used to observe the uniaxial compression process of coal samples with different cyclic cold leaching cycles. Based on the coupling relationship between porosity and uniaxial compressive strength，a damage mechanics model was established to reveal the evolution law of mechanical properties and mechanism of coal structure damage caused by cyclic cold leaching. The results show that 1 there are three stages in the process of uniaxial compression:the stage of pore closure，the stage of pore expansion，and the stage of failure and its development. In the stage of pore closure，the compression deformation of coal sample increases gradually with the increase of cyclic cold leaching period. 2 Compared with the stress-strain curves of coal samples with⁃ out cold soaking，the uniaxial compressive strength and brittleness of coal samples after cyclic cold soaking decrease， and the cyclic cold soaking period is negatively correlated with the uniaxial compressive strength and brittleness. 3 Using the ABAQUS software for numerical simulation，the mechanical model of coal sample cold immersion damage is established. It is found that under the liquid nitrogen cold immersion environment，the coal matrix shrinks，and the stress concentration phenomenon appears at the crack tip of coal. When the stress intensity factor at the crack tip ex⁃ ceeds the fracture toughness of coal， the crack will expand. Liquid nitrogen cycle cold leaching can damage and change the pore and fracture structure of coal samples，and promote the deterioration of mechanical properties of coal，which will provide an important theoretical reference for coalbed methane extraction and rock burst prevention.