Law And Control Of Strata Behavior In Fully Mechanized Working Face With Shallow Depth And High-intensity Mining In Yushen Mining Area

The occurrence characteristics of thin bedrock and thick loose layer of shallow coal seam can easily lead to accidents such as cutting and falling of the roof in the working face.However,the low gas,low dip angle and simple geological structure also provide conditions for the high-intensity mining.It successively produced a number of shallow depth and high-intensity mining working faces in Shendong and Yushen mining areas in China.Because there are few studies on the law and control of strata behavior in working face with shallow depth and high-intensity mining,this dissertation,taking the fully mechanized working faces of 4-2 coal seam in Liangshuijing coal mine in Yushen mining area as the engineering background,adopted combination methods of theoretical analysis,numerical simulation,physical similarity simulation and field practice to analysis the influence of working face length and working face advancing speed on the strata movement and strata behavior in fully mechanized working face with shallow depth,and then the principle and technology of strata behavior control in fully-mechanized mining with shallow depth and high-intensity mining was also researched.The research fruits can further enrich the strata control theory of coal mine.The innovative results of this dissertation are as follows:(1)Based on the elastic thin plate theory,the distribution law of the moment in the main roof was analyzed,which came to a conclusion that break form of the main roof in fully mechanized working face with longer working face length is vertical “O-X”break and then transverse break.That makes the main roof is a statically indeterminate bearing structure.Then according to the principle of internal force distribution in plate and static equilibrium theory,the relationship between the main roof stability coefficient and working face advancing distance,working face length and overburden load of main roof were obtained.Thus the reduction mechanism of the main roof stability in fully mechanized working face caused by longer working face length was revealed.(2)Influence of working face length on strata behavior of the fully mechanized working face with shallow depth,such as strata movement,roof subsidence,abutment pressure and coal wall failure were analyzed.With the increase of the working face length,the intensity of strata movement,roof subsidence,abutment pressure and coal wall failure increase in varying degrees.However,when the working face length reaches a certain value,the influence is gradually reduced and stabilized.Thus the occurrence mechanism of bigger strata pressure,coal wall spalling and roof falling in the fully mechanized working face with longer working face length was revealed.(3)Influence of working face advancing speed on strata behavior of the fully mechanized working face with shallow depth,such as strata movement,roof subsidence,abutment pressure and coal wall failure were analyzed.With the increase of the working face advancing speed,the inadequate adjustment of stress and deformation of surrounding rock reduce the amount of strata subsidence,coal wall spalling and the strata behavior intensity,but the stress concentration factor of surrounding rock in working face increases.However,when the working face advancing speed reached a certain value,the influence is gradually reduced and stabilized.(4)The principle of strata behavior control for fully mechanized working face with shallow depth and high intensity mining was proposed.It is the minimum of the amount of work done on the support system(coal wall and hydraulic support)by the overburden potential energy.In the first weighting stage of fully mechanized working face,precrack blasting technology is used to release and convert the bigger elastic energy of overlying strata.In the periodic weighting stage,the operating parameters of the hydraulic support should make the strata stable bearing structures to reduce the amount of work done on the support system and keep the support system stable.The control technologies effectively reduces the intensity of strata behavior in fully mechanized working face with shallow depth and high-intensity mining,such as weighting over great extent,coal wall spalling,etc..