Research And Application Of The Fracture And Turbulence Law Of The Main Roof Plate Structure Of The Stope

The incidence of mine roof accidents occupies a high position in all kinds of accidents,which is a serious threat to coal safety mining.In this paper,the fracture law?including fracture position,fracture sequence and fracture form?,the condition of instability catastrophe,fracture disturbance?rebound compression?law and early-warning method and its application to plate structure of main roof of the goaf with elastic foundation boundary are studied by combining and using the method of theoretical calculation and analysis,laboratory experiment as well as field investigation and measurement,etc.The main research contents of the thesis are as below.The mechanical models of plate structure of main roof with six kinds of elastic foundation boundaries are established.Based on the fracture criterion of primary moments,the fracture law of mechanical model of plate structure of main roof with six kinds of elastic foundation boundaries and its influencing factors are obtained and calculated respectively with the finite difference method.The mechanical model of trapezoidal voussoir plate structure stability of main roof in the central region of the goaf is established.And the instability conditions of the trapezoidal plate and the minimum support resistance of the support are calculated.In addition,the mechanical model of time and space evolution law of rebound compression field and fracture of plate structure of main roof is established.The relationship between the volume and zone of rebound compression and the range and degree of the fracture of rock plate as well as the time and space evolution law of rebound compression field in the process of roof fracturing are obtained by calculating.The monitoring area and index of the rebound compression field are put forward.And the corresponding early-warning method of roof disaster is formed.The achievements have been successfully applied to Jinhuagong Mine.The main conclusions are as follows?the thickness of main roof is h;the elastic modulus of main roof is E;and the elastic foundation coefficient is k?:?1?The fracture law of plate structure of main roof of the first working face with elastic foundation boundary: The law is determined by k,the span L and the stiffness D of the main roof.When the fracture type and condition of main roof of longwall working face is?k/D?^1/4L>9.6,long side ahead of the coal wall?central region?long side ahead of the coal wall or short side ahead of the coal wall?short side ahead of the coal wall?central region;when?k/D?^1/4L<9.4,central region?long side ahead of the coal wall?short side ahead of the coal wall;when?k/D?^1/4L =?9.5±0.1?,the central region of main roof and long side ahead of the coal wall nearly fracture at the same time;concerning the square working face,when?k/D?^1/4L>10.5,the area of four sides ahead of the coal wall fractures firstly;when?k/D?^1/4L<10.1,the central region of main roof fractures firstly;when?k/D?^1/4L =?10.3±0.2?,the area of four sides ahead of the coal wall and the central region of main roof nearly fracture at the same time.?2?The fracture law of plate structure of main roof of short side of the goaf?coal pillar?with elastic foundation boundary: ?The width of the coal pillar L_m and the pillar support coefficient k_m only obviously affect the fracture form of main roof in coal pillar side and the whole main roof.?When the thickness h and elastic modulus E of main roof are smaller and the values of L_m and k_m are larger,the upper surface of main roof in the coal pillar area will fracture,so the fracture sequence is that the upper surface of long side area ahead of coal wall?lower surface of central region of the goaf or upper surface of short side area ahead of coal wall in solid coal side?upper surface of coal pillar area,and the final fracture form is the type of asymmetric “O-X”.? When the values of E and h are larger and the values of L_m and k_m are smaller,the upper surface of main roof in coal pillar area will not fracture,so the fracture sequence is that the lower surface of central region?upper surface of long side area ahead of coal wall?upper surface of short side area ahead of coal wall in solid coal side,and the final fracture form is the type of asymmetric “U-X”.?3?The fracture law of plate structure of main roof of long side of the goaf?coal pillar?with elastic foundation boundary: ?The width of the coal pillar L_p and the pillar support coefficient k_p can not only change the values of primary moments in central region and solid coal side but also obviously affect the fracture form of main roof in coal pillar area and the whole main roof.?When the thickness h and elastic modulus E of main roof are smaller,the values of L_p and k_p are larger and the span L is larger,the fracture line parallel to the axial direction of the coal pillar will appear in the main roof in coal pillar area.So the fracture sequence is that upper surface of long side area ahead of the coal wall in solid coal area?the lower surface of central region of the goaf in coal pillar side?upper surface of long side coal pillar area?upper surface of short side area ahead of the coal wall,and the final fracture form is the type of asymmetric “O-X”.? When the values of E and h are larger,the values of L_p and k_p are smaller and the value of L is smaller,the fracture line parallel to the axial direction of the coal pillar will not appear in the main roof in coal pillar area.So the fracture sequence is that the lower surface of central region of the goaf in coal pillar side?upper surface of long side area ahead of the coal wall in solid coal area?upper surface of short side area ahead of the coal wall,and the final fracture form is the type of asymmetric “C-X”.?4?The fracture law of plate structure of main roof of two short sides of the goaf?coal pillar?with elastic foundation boundary: ?The two sides coal pillars support coefficients k_m1,k_m2 and the widths L₁,L₂ of the two sides coal pillars only obviously affect the values and positions of primary moments of main roof in coal pillar area respectively.?When the thickness h and elastic modulus E of main roof are larger and the values of L₁,k_m1,L₂ and k_m2 are smaller,the upper surface of main roof in the two sides coal pillar area will not fracture,so the fracture forms are that lower surface of central region in weaker coal pillar side?upper surface of long side area ahead of solid coal in weaker coal pillar side,and the final fracture form is the type of asymmetric “?-X”.? When the values of E and h are smaller and the values of L₁,k_m1,L₂ and k_m2 are larger,the upper surface of main roof in the coal pillar area will fracture,so the fracture forms are that upper surface of long side area ahead of coal wall in weaker coal pillar side?lower surface of central region in weaker coal pillar side?upper surface ahead of coal pillar area in stronger coal pillar side?upper surface ahead of coal pillar area in weaker coal pillar side?or no fracture?,and the final fracture form is the type of asymmetric “O-X”?or asymmetric “U-X”?.?5?The fracture law of plate structure of main roof of two long sides of the goaf?coal pillar?with elastic foundation boundary: ?The two sides coal pillars support coefficients k_c1,k_c2 and the widths L_c1,L_c2 of the two sides coal pillars can not only obviously affect the values of primary moments in coal pillar area and the appearance of the fracture line parallel to the axial direction of the coal pillar but also obviously affect the values of primary moments of short side region and central region.?When the thickness h and elastic modulus E of main roof are larger and the values of L_c1,k_c1,L_c2 and k_c2 are smaller,upper surface of main roof in zone 1 and zone 2 of coal pillar will not fracture and the fracture form is the type of asymmetric “||-X”.When the values of E and h are smaller and the values of L_c1,k_c1 are smaller,upper surface of main roof in zone 1 of coal pillar will not fracture,but upper surface of main roof in zone 2 of coal pillar will fracture,so the fracture form of the working face is the type of asymmetric “C-X”.When the values of L_c1,k_c1,L_c2 and k_c2 are larger and the values of E and h are smaller,the fracture form is the type of asymmetric “O-X”.?6?The mechanical model of plate structure of main roof with all kinds of elastic foundation boundaries satisfies the law of the ratio invariance.When the ratio k/?Eh³?is constant?When the value of k changes,one or two of E and H will all change.And the weakening coefficient of coal pillar keeps a certain value constant.?,the values of primary moments of main roof are constant and fracture positions of main roof are also unchangeable.?7?Trapezoidal voussoir plate structure stability of main roof of the stope?The catastrophic condition of the rotary instability of trapezoidal voussoir plate structure of main roof of the stope:????The catastrophic condition of the sliding instability of trapezoidal voussoir plate structure of main roof of the stope:????8?The time and space evolution law of rebound compression of first fracture of plate structure of main roof with elastic foundation boundary:?When the fracturing of plate structure of main roof with elastic foundation boundary occurs in the long side area ahead of the coal wall,the following zones will be generated in turn at the periphery of the fracture line,namely,“semi-ellipse rebound zone?I?”?“elliptical ring compression zone at the outer boundary”?“elliptical ring rebound zone?II?”?“elliptical ring compression zone”.?The morphological characteristics of first order rebound zone generated by the graded fracturing are obviously different from the morphological characteristics of rebound zone generated by the first fracturing.When the length of first fracture is smaller and the length of second fracture is smaller,the following zones will be generated in turn at the periphery of the fracture line,namely,“first order M-type rebound zone”?“elliptical ring compression zone at the outer boundary”?“second order elliptical ring rebound zone”.When the length of first fracture is larger and the length of second fracture is larger,the following zones will be generated in turn at the periphery of the fracture line,namely,“first order M type rebound zone”?“ring 8 type compression zone at the outer boundary”?“second order ring 8 type rebound zone”.?9?The time and space evolution law of rebound compression of periodic fracture of plate structure of main roof with elastic foundation boundary:?When the periodic fracturing of plate structure of main roof with elastic foundation boundary occurs ahead of the coal wall,the following zones will be generated in turn at the periphery of the fracture line,namely,“first order semi-ellipse rebound zone”?“C type compression zone at the outer boundary”?“second order C type rebound zone”?“C type compression zone”,and the distance between the outer boundary of second order rebound zone and the front compression area is close to the same.?The morphological characteristics of second order rebound zone generated by the graded fracturing are obviously different from the morphological characteristics of rebound zone generated by the first fracturing.When the length of first fracture is smaller and the length of second fracture is smaller,the following zones will be generated in turn at the periphery of the fracture line,namely,“first order M type rebound zone”?“C type compression zone at the outer boundary”?“second order C type rebound zone”.When the length of first fracture is larger and the length of second fracture is larger,the following zones will be generated in turn at the periphery of the fracture line,namely,“first order M type rebound zone”?“M type compression zone at the outer boundary”?“second order M type rebound zone”.?10?The common points of the time and space evolution law of rebound compression field of first fracture and periodic fracture of plate structure of main roof with elastic foundation boundary:?The rebound amount of central region of rebound zone?I?in the front of the fracture line is the largest,and the end region of fracture line is the compression zone.?The fracture degree of main roof doesn't basically change the distribution forms of the rebound compression zone,and the greater the fracture degree is,the greater the rebound amount will be.? The distance between the inner boundary line and the outer boundary line of rebound zone?II?is basically equal and rebound zone?II?has encircled the entire “hanging roof area”.So the rebound compression information generated by the fracturing of main roof ahead of the coal wall can be detected in the two roadway regions and adjacent roadway regions,and the rebound amount of rebound zone?II?increases first and then decreases from the inner boundary line to the outer boundary line.?11?The relationship between the fracturing of plate structure of main roof and the rebound compression zone has been verified by similarity simulation experiment.?12?The method system containing “one synchronization,two delays,two zones,two indexes and two controls” of the early warning of roof disaster is formed,namely,the fracturing and rebound compression of main roof occur at the same time;the obvious weighting of working face falls behind the fracturing and rebound compression of main roof;the method of stress index or displacement index is used to monitor rebound compression information in the two roadway regions and adjacent roadway regions and prevent the disaster of roof cutting and rotary instability of main roof occurring.?13?By means of applying the conclusions which have been made to Jinhuagong Mine,it has been obtained that sliding instability occurs easily in the trapezoidal voussoir plate structure of main roof in 8707 working face.By monitoring the information of rebound compression and based on theoretical analysis,the fracturing time and position of main roof ahead of the coal wall has been accurately judged.So it provides the time and space guarantee for preventing the occurrence of disaster accident of roof cutting of main roof with large area and the safety mining of the working face is also realized.