High Temperature And High Pressure Deformation Experiment And Ductile Deformation Mechanism Of Coal

In this paper,the Suxian mining area of Huaibei coalfield,which was of complex tectonic structures and widespread tectonically deformed coal,was selected as the key research area,and the scientific issue of “the geological control effect and ductile deformation mechanism of coal” was closely centered on.Based on pertinent field and coal mine geological works and related experimental test,the regional tectonic characteristics,the characteristics of tectonic zoning and the formation and evolution mechanisms for the study area were analyzed.The development characteristics of tectonically deformed coal in different tectonic zones was discussed.The stress-strain environment of coal deformation was profoundly revealed by the comprehensive study of palaeo temperature and differential stress estimation of calcite in tectonic rocks,and the tectonic control of coal deformation was discussed in depth.The tectonic dynamic mechanism and developmental model of ductile deformation structural coal formation in the Suxian mining area were proposed.The experimental studies of coal deformation under high temperature and high pressure were carried out systematically.The ductile deformation mechanisms of bituminous coal in Suxian mining area and its geological control effects were revealed through the comparative study of the experimental and geological control factors of the formation of natural and experimental deformed coals.The main results are as follows:(1)The tectonic zoning and deformation characteristics of the Suxian mining area were revealed.The tectonic deformation of Suxian mining area is controlled by thrust nappe structure,which was divided into four tectonic zones with deformation gradual weakening from east to west.The deformation of the Sudong NNE-trending tightly closed fold-fault complex tectonic zone in the overlying system is the strongest;The deformation of the SE fold-fault complex tectonic zone in the south of the Suinan syncline is strong,with the characteristics of “fold-fault assemblage and east-west differentiation”;the superimposed fold tectonic zone at the turning end of Sunan syncline was superimposed by the NWW-trending secondary broad-gentle folds;structures of monoclinic weak tectonic deformation zone in the NW wing of Sunan syncline is relatively simple.(2)The tectonic dynamic mechanism and developmental model of ductile deformation structural coal formation in the Suxian mining area were proposed.The structural deformation of the coal seam in the Suxian mining area was in the stressstrain environment of low temperature and low pressure and horizontal compression stress from E to W.It also has an overall tendency to gradually weaken from E to W.The NNW tightly closed fold-fault complex tectonic zone has strong deformation of coal,with widespread ductile deformation structural coal.The coal deformation of the SE fold-fault complex tectonic zone in the south of the Suinan syncline is gradually weakened from the E to the W,and the ductile deformation structural coal developments in the strong deformation zone.The superimposed fold has a significant effect on the development and control of the ductile deformation structural coal,in the superimposed fold structural deformation zone at the turning end of Sunan syncline.In the NW wing monoclinic weak tectonic deformation zone,the ductile deformation structural coal is only partially developed.The dynamic mechanism,shear stress induced by bedding extrusion of ductile deformation structural coal formation was proposed,as well as the developmental model of ductile deformation structural coal,which is the main bedding layer ductile shear deformation of Thick layer,Thin layering and Sandwich layer enhanced type,and the supplement oblique shear deformation of shear joint and reverse fault.(3)The influence of experimental deformation conditions on coal ductile deformation was revealed.Based on the stress-strain environment of ductile deformation structural coal formation,the high temperature and high pressure deformation experiments of coal by bedding shear and bedding compression stress were carried out systematically.Through the softening experiment,the softening temperature of several coal grades was obtained,reflecting that the low-medium coal grade has the characteristics of low softening temperature and strong ductility.It was revealed that under the action of bedding and oblique shear stress,coal deformation,affected by factors such as strain hardening of solid medium and high temperature softening,transited from the local dominant shear ductile deformation zone to the ductile deformation,such as directional cataclastic flow,plastic rheology and wrinkle,with density of shear fracture increases and the size of the fracture decreases.(4)Through the comprehensive analysis of experimental deformation conditions and geological environment,the geological control mechanism of coal ductile deformation was revealed.It is considered that shear stress is the key factor affecting coal ductile deformation.Confining pressure and temperature can promote coal ductile deformation,leading to the ductile deformation,such as directional cataclastic flow and wrinkle;the low temperature softening property of coal,the original layered structure and the difference in mechanical properties of the medium are important internal factors for ductile deformation.Under the action of compressive stress,the derived bedding and oblique shear stress are mainly converted into strain energy,which causes the coal macromolecular structure to form secondary structural defects and ductile deformation of stress condensation.