Research On The Mechanism Of Rock Burst Occurring In "Three Hard" Coal Seam Of Datong Coal Mining Area

Rock burst is one of the major dynamic disasters of coal mine. Datong Coal Mining Area with the hard seam, the hard roof, and the hard bottom is a typical one under the condition of "three-hard" coal seam. At present rock burst is a key factor which restricts safe and efficient production in the area,but the research on the mechanism of rock burst occurring in this condition is hardly found. Based on the existing research results and combined with the actual situations of Datong Coal Mining Area, this thesis, through on-the-spot investigation, analysis of influence factors of rock burst, measurement and research on the bursting liability and ground stress, as well as numerical simulation, studies the mechanism of rock burst's occurrence under the condition of "three-hard" coal seam in a systematic manner, so as to provide theoretic bases for the control and prevention of rock burst occurring in the condition. The following main conclusions have been drawn:(1) By determination of physical and mechanical properties and judgment of bursting liability of coal, roof and floor of Xinzhou, Tongjialiang and Meiyukou Coal Mine in Datong Coal Mining Area, and research on current identification indicators of bursting liability, this thesis proposes new index of bursting liability, dump energy delivery speed index.(2) Ground stress is measured on site with the method of hollow inclusions strain gauge. The results of test show that the horizontal tectonic stress is comparatively large and dominant in Datong Coal Mining Area, and the direction of maximum horizontal compression stress is basically SE—NW, and its alignment is in between N-W and NN-W,and its maximum changes between 324.9°-331.7°. The lateral pressure coefficients of four measuring point change between 1.500-1.789.(3) Numerical simulation has discovered that tectonic stress has a great influence on rock burst. Under the action of tectonic stress, coal and rock will form stress concentration and cause rock burst more easily. As for the tunnel, when the direction of principal stress is perpendicular to axial of tunnel, the vicinage of coal wall will form larger horizontal stress gradient and cause rock burst easily. Therefore, it must be noted that the tunnel should not be perpendicular to the direction of maximum horizontal stress when it is arranged.(4) Rock burst in Datong Coal Mining Area has not only general characteristics of rock burst (suddenness, diversity, complexity, destructiveness), but also distinct characteristics of Datong, i.e. three-hard, shallow show site of rock burst, rock burst occurring in the next hierarchical tunnel greater than in the previous one etc.(5) According to the features of rock burst in Datong Coal Mining Area, rock burst in this area can be divided into four basic types, i.e. two coal walls burst, floor burst, two coal walls and floor burst, and small block ejection.(6) The thesis studies the influence factors of rock burst, which mainly includes two major factors, i.e. natural geological conditions and mining technology conditions. Rock burst occurring in Datong Coal Mining Area is affected by both factors.(7) The main reasons causing the two walls burst of tunnel in Datong Coal Mining Area includes mining method, stress of coal, support intensity and impact of mining.(8) Under the condition of "three hard", it is thought that with the expansion of the mined-out area, high pressure, which is imposed on the pillar around tunnel, will make clamping effect on coal seam. Vibration and rebound of the roof will cause separation between the wall and the roof.(9) The mathematical and mechanics model is established, numerical simulation is applied, and the rock burst mechanism of the overall removal of coal tunnel wall is studied in the thesis.Under the condition that vertical cracks exist or will appear in a certain depth of the tunnel walls, horizontal displacement of the tunnel walls is basically proportional to horizontal load, and horizontal displacement during the coal bed being separated from the roof and the floor is much more obvious than the horizontal displacement with no separation. Besides, the former grows much faster than the latter.(10) The phenomenon of hard floor burst is explained in the theory of Key Layer, and influence factors are finally found out. After analysis of numerical simulation, the thesis considers that with the increase of tunnel width, maximum horizontal tensile stress occurs in deeper position of the bottom, and it will cause sudden fracture of floor key layer, and eventually lead to the occurrence of rock burst.New points of the thesis are as follows:(1) For the first time, the thesis proposes the conception of rock burst of "three hard",and clarifies the features of rock burst in Datong Coal Mining Area. The rock burst with conditions of "three-hard"and shallow is classified,and the influence factors are studied.(2) For the first time, the rock burst mechanism of the overall removal of coal tunnel wall is studied. With the establishment of mathematical and mechanics model and analysis of numerical simulation, the conditions and the laws of rock burst are found.(3) For the first time, the phenomenon of hard floor burst is explained in the theory of Key Layer, and influence factors are found out. With the analysis of numerical simulation, the conditions of rock burst are found out.