Research On The Mechanism And Control Technology Of Floor Heave In Thick Seam Gob-side Entry Retaining In Gucheng Mine

Based on the engineering background of N2301 auxiliary transportation along the thick seam of Gucheng Coal Mine,this thesis adopts a combination of field investigation,laboratory tests,theoretical analysis,and numerical simulation to establish mechanical models of floor heave in front of and behind the gob retaining roadway,and explores the mechanical mechanism of the roadway floor heave during the entire process of gob retaining roadway in thick seam.Based on the mechanical analysis of the floor heave mechanism,a floor loosening blasting pressure relief floor heave control technology with improving the stress state of surrounding rock as the core is proposed.In order to ensure a good rock mass fracturing effect by loose blasting,the parameters of the HJC constitutive model for the mudstone on the roadway floor are determined based on the laboratory basic mechanical parameter testing results,and the numerical simulation of rock mass fracturing by loose blasting is conducted.A reasonable loose blasting pressure relief technical scheme is designed based on the numerical simulation results of crack propagation by loose blasting,and on-site industrial tests are conducted.Based on the above research,the main research results obtained in this article are as follows:(1)Through on-site sampling and laboratory mechanical tests,the structural characteristics and mechanical parameters of surrounding rock in the N2301 auxiliary transportation chute are determined.The results show that the roadway roof has a thick and relatively high hardness sandstone layer,which is a basic roof and is not easy to break.The lithology of the floor rock layer is relatively soft and weak compared to the roof rock layer,and the integrity of the rock layer is also low.After retaining the roadway along the goaf,the rock pressure appears violently,and the roadway floor is prone to horizontal stress concentration to produce a compressive flow type floor heave.(2)By introducing Rankine’s earth pressure theory,the mechanical models of floor heave in front of and behind gob-side entry retention are established respectively.Based on the mechanical model of floor heave in gob-side entry retention,the calculation formula for the effective sliding force of the floor on the solid coal side and the side fill body side of the entry is derived.Combined with the stress evolution law of the floor of gob-side entry retention,it is concluded that the compressive effect of horizontal stress is the direct cause of the floor heave in gob-side entry retention,The change of vertical stress between the side of the roadway coal wall and the side of the roadway filling body is the fundamental cause of the roadway floor heave left along the goaf.Based on this,a floor loosening blasting pressure relief technology aimed at improving the stress state of the surrounding rock is proposed to control the roadway floor heave.(3)Using the basic physical and mechanical parameters of mudstone measured in the laboratory,the strength parameters,strain rate effect parameters,and pressure parameters of mudstone were determined through theoretical calculation.The complete HJC constitutive model parameters of coal mine mudstone were determined based on empirical parameter values.The HJC model of mudstone was improved by adding failure shear strain and failure tensile stress failure criteria,Using LS-DYNA numerical simulation software,the entire process of the formation of the fragmentation zone and the fracture zone in loose blasting was simulated and reproduced.The simulation results showed that the radius of the fracture zone formed by mudstone loose blasting was 205 cm,57 times the radius of the blast hole.(4)Based on the simulation results of crack propagation in loose blasting,the key parameters of pressure relief floor heave control technology in loose blasting are determined.An industrial test of pressure relief in loose blasting of the roadway floor is conducted in the test section.Through on-site measurement of the deformation amount of the roadway floor,it is concluded that when the roadway measurement point in the pressure relief section of the floor loose blasting is 250 m behind the working face,the roadway floor heave amount is 158 mm,the industrial test results verify the reliability of the floor looseness blasting pressure relief technology in controlling the floor heave of gob-side entry retaining in thick coal seams.This thesis has 50 diagrams,7 tables,and 91 references.