Study On Overlying Strata Movement Mechanism Of Gob-side Entry Retaining And Entry Retention Measures In Thick Three-soft Coal Seam

With the advantages of smaller engineering quantities,less coal losses,timely production and high security,gob-side entry retaining(GER)is an important roadway layout method to realize green and efficient mining in the coal industry.However,due to the influence of multiple dynamic pressure disturbance and long service time,the phenomenon of mine pressure appears violently,even affect the regular service.Entry driven along the bottom of thick coal seam can minimize the waste of coal,but the soft top coal of GER makes the stability influencing factors more complex,and the difficulty of surrounding rock control further increases.Taking GER along bottom driving in thick three-soft coal seams as the object,this dissertation reveals the laws of overlying rock movement,surrounding rock deformation and stress evolution under different GER measures by the methods of theoretical analysis,numerical simulation and laboratory test.The technology of relief-filling synergic entry retaining(RSER)was proposed and successfully applied in the field.The main research achievements and conclusions of the dissertation list as follows:(1)The mechanical parameters of roadway surrounding rock were measured by selecting Zhaojiazhai coal mine and Peigou Coal Mine which are the mines of thick threesoft coal seams.The three-dimensional loading device of large-scale coal and rock samples and grouting simulation device were developed to test the mechanical parameters of broken coal samples after grouting under stress disturbance.The coal sample modified by grouting,the strength and anti-deformation characteristics can be significantly improved.(2)Based on the Winkler elastic foundation beam theory,the mechanical model for analyze the main roof lateral fracture position and the influencing factors was established.The stability criterion of arc triangle block structure under the GER measures with roadside filling and roof cutting automatically formed were established.The two entry retaining methods are significantly affected by geological factors under the condition of thick three-soft coal seams,fracture position and instability coefficient of arc triangular block have several variable.The main roof structure is prone to instability and difficult to control.(3)In view of the poor stability of the roof structure under the above two entry retaining modes,the RSER technology was proposed based on the idea of ’ controlling the main roof breaking form,changing the residual main roof size at the lateral gob and maintaining the integrity of the entry roof ’.The RSER technology completely cuts off the main roof along the predetermined position,and constructs the filling body in the entry.Theoretical analysis shows that the roof structure which beneficial to the stability of gob-side entry can be formed regardless of the coal seam,immediate roof and main roof conditions.The key to RSER is to reasonably design the strength and width of the filling body.(4)The numerical calculation models were established to analyze the surrounding rock deformation characteristics of three GER measures in thick three-soft coal seams with different rock structures.The study found that: the thickness of coal seam,immediate roof and main roof have a significant impact on the entry deformation under the modes of GER with filling body and GER with roof cutting.Under mode of RSER,the thickness of coal seam has a certain impact on roadway deformation,while the thickness of immediate roof and main roof has no significant impact on surrounding rock deformation.The plane similar simulation verification results show that: the GER with road-side filling body is the most affected by stress disturbance,followed by the roof cutting roadway,and the unloading retaining roadway is the least.The stress distribution of gob-side entry was changed by RSER,and the stress around the roadway was significantly reduced in front of and behind the working face The influence of dynamic pressure caused by overlying strata on roadway was significantly reduced,and the roadway quality was significantly improved.(5)Aiming at the characteristics of low strength and fragmentation of surrounding rock in thick three-soft coal seam,the hole forming device and rapid grouting device were developed.The parameters such as charging,blasting and drilling layout were designed.Concrete filling material with rapid solidification and high initial strength was prepared.The high stability bearing structure of "grasping the floor,strengthening the middle and fixing the roof" is designed to avoid the possible sliding and damage of the filling body.The key technology of RSER in thick three-soft coal seam has been formed,corresponding results have been successfully applied in engineering practice,and the surrounding rock control effect is satisfactory.There are 118 figures,11 tables and 166 references in the dissertation.