| As an important part of high-efficiency and green mining technology of coal resources,no pillar or small pillar roadway protection technology has been used more and more in recent years.However,in the production practice,especially in the thick coal seam mining of western mining area,aiming at the problem that it is difficult to determine the pillar size of roadway along goaf,the combination of field test,theoretical analysis,similar simulation,numerical simulation and field practice is used Methods: the bearing mechanism of coal pillar in gob side entry of fully mechanized top coal caving face was studied,and a theoretical calculation method of coal pillar width including parameters of coal seam mining height,overburden structure,load characteristics,coal strength and roadway size was put forward,which is suitable for optimization of coal pillar size in the whole life cycle of gob side entry.Starting from the load of overlying strata supported by pillars in gob side entry,the following research work is carried out:(1)the law of strata pressure appearance of different width pillars in gob side entry is revealed through the observation of strata pressure;(2)the theoretical research on the key strata of goaf tendency is carried out and the calculation formula of pillar stress is put forward;(3)the similar simulation and digital speckle test methods are integrated to study the movement of overlying strata of goaf tendency Characteristics,regional stress and deformation characteristics of coal pillars,and the influence of interlayer friction effect on the stability of coal pillars;(4)numerical simulation study on the change rule of stress field and displacement field of surrounding rock of different width coal pillars along goaf;(5)optimization design and engineering practice of coal pillars along goaf.Through the research of this paper,the following achievements have been achieved:(1)Based on the actual measurement of the mine pressure law of the gob side entry of the 8m and 15 m wide coal pillars in the fully mechanized top coal caving face,it is concluded that when the width of the coal pillars is 8m,the deformation of the coal pillars is the main displacement of the two sides,and when the width of the coal pillars is 15 m,the deformation of the solid coal is the main displacement of the two sides.The width of the coal pillars has a significant impact on the mine pressure appearance of the roadway.(2)A theoretical model based on the inclined key block structure is proposed.The mechanical analysis and simplified calculation of the key block are carried out,and the stress structure of the key block is obtained.According to the principle of deformation coordination,it is determined that the bottom of the settlement zone and the surrounding rock form a large bearing structure similar to a right triangle.When the roadways along the goaf are arranged under the large triangle structure,the small right angle trapezoid structure above the coal pillar determines the stress of the coal pillar.According to the area sharing method,the stress of coal pillar is calculated.The stress of coal pillar is directly proportional to the area of right angle trapezoid above and inversely proportional to the width of coal pillar.(3)The results of similar simulation and speckle test show that the height of fracture zone of overlying strata(the height of right angle trapezoid)is 7.5 times of mining height,and the obtuse angle of right angle trapezoid is 105.6 °.After the overburden is stable,the horizontal displacement of coal pillar increases from top to bottom in turn;during the process of driving along the goaf,there is transverse shear failure at the bottom of coal pillar.Under the action of compression shear load,the surrounding rock of coal pillar changes alternately in tension and pressure.With the increase of shear stress,the strength of coal body decreases approximately linearly.(4)The numerical simulation shows that when the mining height is 10 m,the stress concentration coefficient of advance support is 1.78(dynamic load coefficient of coal pillar when mining);the plastic damage of surrounding rock,the amount of roof subsidence decrease with the increase of coal pillar width;when the width of coal pillar exceeds 10 m,the amount of surrounding rock plastic area and roof subsidence decrease;the stress peak value of coal pillar increases first and then decreases with the increase of coal pillar width.Numerical simulation shows that 10 m coal pillar is reasonable.(5)The new type of coal pillar calculation formula is used to check the safety of the coal pillar along the gob in the 30105 working face of Liuxiang coal mine.The calculation shows that the safety factor of the 8m coal pillar is less than the dynamic load factor of the coal pillar when mining 1.78;the theoretical calculation width of the coal pillar through the safety check is 9.4m,which is close to the actual measured width of the coal pillar 9.5m.It is suggested to reserve 10 m coal pillar and strength the side support to ensure that the safety factor is greater than the dynamic load factor.The field application shows that the maximum deformation of the coal pillar is less than 51 mm,and the coal pillar is stable and reliable. |
