Wave Mechanism Of The Dynamic Load From The Activation Of The Hard Roof And Control Of Roadway Adjacent To Gob

Side abutment stress,front abutment stress and dynamic stress can be generated by the movement of the overlying strata.Under the synergistic effect of the three stress field,local coal and rock is in the superposition bearing state of static and dynamic load,which may easily result in dynamic disasters in engineering.Under the condition of the large deformation of the roadway adjacent to the gob,the comprehensive methods of theoretical analysis,mechanics analysis,numerical calculation,in situ monitoring and field test were used to solve the following four problems.Firstly,formation mechanism of the dynamic stress from the mining activation of the lateral hard roof structure was analyzed.Secondly,propagation of the dynamic stress in the stratums nearby the coal field was revealed.Thirdly,large-deformation mechanism of the roadway adjacent to the gob under the superposition of the static and dynamic stress was researched.Finally,the control technology of weakening the dynamic and static load for the roadway adjacent to the gob during mining activity was developed.Formation mechanism of the dynamic stress from the mining activation of the lateral hard roof was analyzed.Bearing mechanical model for the structure was established and the instability and fracture criterion of the structure was revealed.The load-bearing structure of the lateral hard roof generates instantaneous fault movement and short-term caving movement when loaded by the mobile front abutment stress,which results in fracture dynamic load and impact dynamic load.Fracture dynamic load presents a linear positive correlation with the cantilever in length and tensile strength,the lower rock structure in thickness,extruding strength and frictional angle,and it presents a linear negative correlation with the thickness of the cantilever.Also,the impact dynamic load presents a negative correlation with the length of the working face,the thickness of the unconsolidated formation,the bulking coefficient of the rock and coal and it presents a positive correlation with the mining height,the recovery coefficient,the cantilever in length,thickness,elasticity modulus,rock structure's loads and the compressional stiffness of the rock in the gob.Propagation and its main influencing factors of the dynamic stress in the stratums nearby the coal field was obtained.Based on the established mechanical transmission model through the structure plane between rocks and the mathematical attenuation model through the homogeneous rock for the dynamic stress,the attenuation effects of the incidence stress wave parameters including incidence angle,wave frequency,the medium properties such as poisson's ratio,density,elasticity modulus and the structure plane properties like the normal stiffness and the shear stiffness on the dynamic stress through the structure plane were studied.In the meanwhile,the attenuation factors of the dynamic stress through the typical homogeneous coal and rocks were fitted and monitored.Based on the analysis above,the tomographic imaging early warning technology of the mining dynamic stress coefficient was put forward.Large deformation mechanism of the roadway adjacent to the gob under the superposition of the static and dynamic stress was simulated.Under the analysis of the bearing condition for the roadway during mining activity,the numerical analytical model used to reveal the synergistic effect of the dynamic and static stress was established and the analytical method of using the dynamic load disturbance intensity to evaluate the response sensitivity of the roadway was proposed.By the studies of the dynamic load disturbance intensity in the stress,the displacement,the plastic zone and the acceleration around the roadway loaded by the superposition of the static and dynamic stress,large deformation mechanism of the roadway was revealed.The algorithm of solving the threshold of the dynamic load response was developed to divide the dynamic load disturbance intensity into "slight disturbance type","medium disturbance type" and "severe impact type".Control technology of weakening the dynamic and static load for the roadway adjacent to the gob during mining activity was developed.Under the condition of the large deformation mechanism of the roadway,the pre-control concept of the standards including eliminating dynamic load and decreasing static load,decreasing static load and bearing dynamic load and decreasing dynamic load and bearing static load was put forward.According to the pre-control concept,the pre-control complete set of technical system consisting of the pre-splitting roof control technology for eliminating dynamic load and decreasing static load,the reduction technology of coal pillar width for decreasing static load and bearing dynamic load and yieldable support technology for decreasing dynamic load and bearing static load was developed to control the large deformation of the roadway.The results of the industry test for the pre-control technology show that the reduction of the dynamic and static stress can control the deformation of the roadway effectively,which decreases the deformation significantly.