Mechanism Research Of The Maximum Horizontal Stress On Rockburst And Its Application

Rockburst is one of the dynamic catastrophe phenomena during coal mining. Especially in fold areas, the catastrophe intensity and the harm induced by rockbursts are more obviously prominent. Through in-situ stress measure and geological survey, research approaches such as numerical simulation, experiments, theoretical analysis and engineering practice were adopted. Experiment on rockburst failure effect of samples under unloading condition in stress field was conducted, mechanism of the critical maximum principal stress on rockburst was presented, rules of distribution of the maximum horizontal stress and mine-induced stress field were studied, and relation between stress field in fold areas and rockburst along with other key influential factors on rockburst of strata of roadway in fold areas were analyzed. Finally, design project of optimizing coalface and roadway layout for preventing rockburst in fold areas were presented and its practice application was given.Rockburst failure effect of samples under unloading condition in stress field was studied with unloading experimental equipment designed and SANS materials testing machine chose. The results show that brittle fracture characteristics of the samples is obvious and sudden under unloading condition. Furthermore, the stress drop, the stress drop rate and intensity of AE&EME signals which closely related to rockburst failure effect are positive correlated to the initial axial stress, the initial lateral stress and uniaxial compressive strength of the samples. That is, much higher the value of the initial axial stress, the initial lateral stress and uniaxial compressive Strength of the samples are , more severe the failure is, the greater energy of the samples releases under unloading condition.From energy dissipation and energy release principles, stress criterion and energy criterion of rockburst failure were analyzed and mechanism of the critical maximum principal stress on rockburst was presented. Based on this, through analysis on variation of the critical maximum principal stress of both sides and floor of roadway under different lateral stress coefficientλ, mechanism of the maximum horizontal stress on rockburst was studied. The results show that, along with increase of the different lateral stress coefficientλ, the value of actual maximum principal stress of both sides of roadway decreases, but the critical maximum principal stress on rockburst increases, so danger of rockburst of both of roadway weakens. The critical maximum principal stress of floor of roadway on rockburst increases, but the value of actual maximum principal stress also increases and increases faster, so danger of rockburst of floor of roadway augments. By FLAC numerical simulation software, rules of distribution of the maximum horizontal stress and mine-induced stress field were studied. The results indicate that the maximum horizontal stress of the axis of fold structure is higher than that of the wing parts and the maximum horizontal stress of the wing parts is higher than that of anticline. The maximum horizontal stress concentrates at hard rock seam, but stress in soft rock seam in the middle of hard rock is correspondingly low. The results also indicate that convergence of stress is more higher when advancing downhill from anticline to syncline compared to advance in the direction of rising. In addition, Mining the coalface near the syncline firstly,then mining the coalface near the wing parts,the concentration of the horizontal stress and abutment stress inboard the coalface near the syncline decreases with different degrees and the affected area of the horizontal stress reduces. Mining the coalface near the wing parts firstly,then mining the coalface near the syncline, the concentration of the horizontal stress and abutment stress inboard the coalface near the syncline are higher.Relation between stress field in fold areas and rockburst was analyzed and other key influential factors on rockburst of strata of roadway in fold areas were analyzed, such as rock compressive strength, the abutment stress and stress waves disturbance. Many rockburst phenomena in fold areas were explained. Based on the above research results, design project of optimizing coalface and roadway layout for preventing rockburst and countermeasure of structure type rockburst prevention in fold areas were presented.Finally, acted as the application example of two coal mines with serious rockburst hazard in fold areas, the distribution of initial stress was studied by the measurement of in-situ stress and numeric simulation, the distribution of the maximum horizontal stress was obtained. Applied the presented idea and countermeasure of structure type rockburst prevention, engineering practice of optimized coalface and roadway layout design as well as weakening roof and coal side for preventing rockburst were studied.